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Enhanced Mobilization of Arsenic and Heavy Metals from Mine Tailings by Humic Acid
Abstract
Arsenic and heavy metal mobilization from mine tailings is an issue of concern as it might pose potential groundwater or ecological risks. Increasing attention recently has been focused on the effects of natural organic matter on the mobility behavior of the toxicants in the environment. Column experiments were carried out in this research study to evaluate the feasibility of using humic acid (HA) to mobilize arsenic and heavy metals (i.e., Cu, Pb and Zn) from an oxidized Pb-Zn mine tailings sample collected from Bathurst, New Brunswick, Canada. Capillary electrophoresis analyses indicated that arsenate [As(V)] was the only extractable arsenic species in the mine tailings and the addition of HA at pH 11 did not incur the oxidation-reduction or methylation reactions of arsenic. A 0.1% HA solution with an initial pH adjusted to 11 was selected as the flushing solution, while distilled water (initial pH adjusted to 11) was used as the control to account for the mobilization of arsenic and the heavy metals by physical mixing and the effect of pH. It was found that the HA could significantly enhance the mobilization of arsenic and heavy metals simultaneously from the mine tailings. After a 70-pore-volume-flushing, the mobilization of arsenic, copper, lead and zinc reached 97, 35, 838 and 224 mg kg(-1), respectively. The mobilization of arsenic and the heavy metals was found to be positively correlated with the mobilization of Fe in the presence of the HA. Moreover, the mobilization of arsenic was also correlated well with that of the heavy metals. The mobilization of co-existing metals to some extent might enhance arsenic mobilization in the presence of the HA by helping incorporate it into soluble aqueous organic complexes through metal-bridging mechanisms. Use of HA in arsenic and heavy metal remediation may be developed as an environmentally benign and possible effective remedial option to reduce and avoid further contamination.
... Humic compounds have the ability to adsorb heavy metals through the mechanism of interaction of metals or other cations with functional groups (Fahmi, 2011). Humic compounds have great potential to be used as bioremediation because they have been shown to be able to reduce heavy metal content due to tailings soil contamination (Wang and Mulligan, 2009). The use of compost as a source of humic acid has a lower economic value with the same level of effectiveness as leonardite (Piccolo et al., 2019). ...
... The phenolic group in biosilica was lower than that of humic acid (Table 1) and did not have a carboxyl functional group that has an important role in heavy metal absorption. At pH 2.5-7, the role of the carboxyl group is very important in metal adsorption, and at pH 8-13.5, the role of the phenolic -OH group in metal binding, but the bond is weak (Wang and Mulligan, 2009). While the bond in biosilica only occurs in the -OH group bond which will bind heavy metals (Lei et al., 2018). ...
... (3) 2(≡Si-OH) Pb 2+ → (≡Si-O−)2Pb 2+ + 2H + The high phenolic -OH content without the presence of a carboxyl group makes the biosilica ability lower than humic acid. The carboxyl group will readily form bonds with metals in the pH range of 2.5-7 and form carboxylic bonds, while the phenolic OH groups will react at pH 8-13.5, but these bonds are weak to metals (Wang and Mulligan, 2009) and in particular, Pb will be easily bound to humic acid at neutral pH (Zhu et al., 2020). ...
Sandy loam soils contain low organic carbon and have low ion adsorption capacity. Under certain conditions, the soils contain heavy metals that are harmful to plants. Soil amendments such as biosilica and humic acid from natural sources are expected to increase the soil adsorption capacity to heavy metals. A simulation experiment consisting of two factors was conducted to explore the effectiveness of humic and biosilica, as soil amendments, in adsorbing heavy metals from soils. The first factor was biosilica dose composing 0 t ha<sup>-1</sup> (S0), 0.5 t ha<sup>-1 </sup>(S1), 1 t ha<sup>-1 </sup>(S2), and 1.5 t ha<sup>-1 </sup>(S3). The second factor was the humic acid dose composing 0 kg ha<sup>-1</sup> (H0), 20 kg ha<sup>-1</sup> (H1), 40 kg ha<sup>-1</sup> (H2), and 60 kg ha<sup>-1</sup> (H3). The humic acid and biosilica were applied to soil contaminated with Pb and Cd. The results showed that the combination of 0.5 t biosilica ha<sup>-1</sup> (S1) and 20 kg humic acid ha<sup>-1</sup> (H1) significantly increased soil pH, organic C content, cation exchange capacity, and reduced the availability of Pb and Cd at 90 days after treatment. The Pb and Cd contents in plant tissue decreased from roots to grains. Humic acid treatment was more effective in absorbing Pb of 86.89-90.49% and Cd of 71.47-76.33% than other treatments.
... Worldwide As concentrations have been widely reported at chronic levels, through different paths, including air, food, water and soil (Wang and Mulligan, 2009;Shakoor et al., 2015;Rahman et al., 2017;Teixeira et al., 2020). The intake of As can lead to serious health issues. ...
... This reactive material has high levels of organic matter, thus conferring a high potential sorption of potentially toxic elements (PTE), including As, proven in Farrell and Jones (2010), Garau et al. (2019) and Tang et al. (2020). Nonetheless, the relationship of organic matter with As immobilization is controversial (Wang and Mulligan, 2009;Bolan et al., 2013;Beesley et al., 2014;Arco-Lázaro et al., 2016;Nandillon et al., 2019). ...
... This may have favored the lower percentages of As sorption by the composts, in agreement with other authors. Wang and Mulligan (2009) reported that the addition of humic acids significantly enhanced the mobilization of As and other PTE from the mine tailings through the formation of organic complexes. Beesley et al. (2014) evaluated the influences of amendments with compost and biochar on the mobility and toxicity of As in contaminated mine soil and concluded that the compost (alone and combined with biochar) stimulated the occurrence of high concentrations of DOC in the pore water; while the impact of biochar in DOC on pore water was small (C is stable and insoluble in biochar). ...
The historic contamination of water and soils by arsenic (As) is an extremely alarming environmental and public health issue worldwide. This study investigated the relationship between As sorption and physicochemical properties of composts and biochars derived from the organic fraction of municipal solid wastes (OFMSW) towards the development of promising sorbents with value-added solid wastes management solutions. The sorbents were characterized and their effectiveness on the As sorption was tested. Several isothermal and kinetic sorption models were used for the prediction of sorption. Composts did not show promising sorption capacities, and in some cases, the As immobilization was practically null. In contrast, biochars achieved higher sorption performance, and the experimental data fitted well on Dubinin-Rabushkevich and Langmuir models, with higher R² values. The maximum sorption capacities of BC700 estimated by such models were 6.495 and 170.252 mg g⁻¹, respectively, whereas those of BC500 estimated by D-R and Langmuir models were only 0.066 and 0.070 mg g⁻¹, respectively. In sorption kinetics, As was retained onto biochars at a faster first stage, reaching equilibrium after approximately 1h and 2h for initial concentrations of 10 and 100 mg L⁻¹. The pseudo-second-order, Ritchie's second-order, Ritchie's, and Elovich models more adequately described the sorption kinetics of As onto biochars with high R² values. Overall, the complexation and precipitation were predominant mechanisms for As sorption by OFMSW-derived biochars. Furthermore, the mathematical models indicated contributions arise from physisorption and external and internal diffusion mechanisms. Although BC700 can immobilize large As amounts, the gastric phase of the oral bioaccessibility test revealed more than 80% of the sorbed As could be released under conditions similar to a human stomach (pH∼1.2). Such conclusions have given important insights about the refining of effective and eco-friendly remediation technologies for the management and rehabilitation of As-contaminated soil and water, particularly in developing countries.
... 4.0 8.0) and/or able to form strong binding (i.e. inner sphere complexes) with metal cations (Ge et al., 2000;Silvetti et al., 2017a;Wang and Mulligan, 2009). Moreover, it was shown that humic substances extracted from compost are able to form As-metal-organic-complexes where divalent or trivalent metal cations (e.g. ...
... Moreover, As and Sb bound to soil particles could be involved in competition phenomena with soluble organic or inorganic anions within compost (e.g. sulphate, phosphate, humic and fulvic acids), leading to As and Sb release in solution (Wang and Mulligan, 2009). The general lack of agreement regarding these issues, likely due to the complexity and heterogeneity of the experiments carried out, highlights the importance of further studies on the interactions between TM, metalloids and organic amendments such as compost. ...
... Indeed, the residual fraction of Ni, Cr and Zn (i.e. the fraction strongly retained by soil, which accounts for the metal fractions very insoluble and/or occluded metal pools) increased with the addition of compost in both soils, and the highest increase was recorded in HS-and TS-MSWC 3% (> 3.7, 3.0 and 4.2% and > 5.0, 4.0 and 5.0% for Ni, Cr and Zn respectively, in HS-and TS-MSWC 3% compared to the respective controls) (Fig. 3). These results highlight an increase of inaccessible and immobilized TM in the MSWC-treated soils (Ge et al., 2000;Wang and Mulligan, 2009). ...
Organic based amendments can be used to reduce metal(loid)s mobility in polluted soils and alleviate possible toxicity phenomena towards soil microbiota. Therefore, the objectives of this study were to evaluate the influence of municipal solid waste compost (MSWC) on the mobility of metal(loid)s in different contaminated soils and to determine the amendment effect on selected soil biochemical and microbial features. To this aim, MSWC was added at two rates (1 and 3% w/w) to different soils sampled in distinct regions of Lebanon (Halba and Terbol, i.e. HS and TS respectively) polluted with metal(loid)s such as As (total concentrations between 31 and 54 mg·kg⁻¹) and Sb (between 93 and 120 mg·kg⁻¹), and trace metals such as Ni, Cr and Zn. After two months of soil-amendment contact, compost addition at both rates significantly increased the non-extractable fractions of As, Sb, Ni, Cr and Zn (e.g. +25% of residual Sb in TS-MSWC 3% with respect to untreated TS), while decreased the environmentally-relevant water soluble and exchangeable fractions of all the metal(loid)s. This effect was more relevant for both soils when 3% MSWC was applied. The amendment addition similarly affected the community level physiological profile (Biolog CLPP) of the respective soil culturable microbial communities, which however showed an opposite trend in the two soils. In particular, compost addition increased the metabolic potential and catabolic versatility of the HS microbial community (compared to the untreated control), while the same proxies were significantly reduced in the amended TS soil. Differently, soil dehydrogenase (DHG), β-glucosidase (β-GLU) and urease (URE) activities were significantly enhanced in both soils treated with compost (e.g. + 17, 45 and 27% for DHG, URE and β-GLU in TS-MSWC 3% with respect to untreated TS). The results obtained showed that the addition of MSWC, particularly at the 3% rate, was effective at fixing the metal(loid)s present in both soils, had a substantial influence on the structure of the soil microbial communities and a positive effect on soil functionality. Taken together the results presented suggest that MSWC can be used as an alternative and environmental friendly amendment for the in situ remediation of metal(loid)s-polluted soils.
... Despite this, it seems well established that organic colloids within compost can bind PTE such as Pb, Cu, Cd and Zn, through a number of adsorption processes involving a variety of functional groups (e.g. carboxylic, phenolic, amine, thiol; Park et al., 2011;Silvetti et al., 2017;Wang and Mulligan, 2009). Likewise, also the water-soluble organic and inorganic fractions of composts can significantly contribute to PTE precipitation as recently highlighted Silvetti et al., 2017). ...
... For instance, competition phenomena, involving inorganic anions within compost (e.g. phosphate and/or sulphate; Diquattro et al., 2018;Manzano et al., 2016), can displace As or Sb from the soil binding sites increasing their labile (and potentially bioavailable) fractions (Tandy et al., 2009;Wang and Mulligan, 2009). Furthermore, As and Sb present in sparingly soluble phases could be involved in the formation of stable complexes with the dissolved organic matter of compost, with the consequent increase of their solubility and mobility (Wang and Mulligan, 2009). ...
... phosphate and/or sulphate; Diquattro et al., 2018;Manzano et al., 2016), can displace As or Sb from the soil binding sites increasing their labile (and potentially bioavailable) fractions (Tandy et al., 2009;Wang and Mulligan, 2009). Furthermore, As and Sb present in sparingly soluble phases could be involved in the formation of stable complexes with the dissolved organic matter of compost, with the consequent increase of their solubility and mobility (Wang and Mulligan, 2009). However, the reduction of labile As and Sb in soils treated with organic matter was previously reported, especially in acidic soils (Manzano et al., 2016;Park et al., 2011). ...
The aim of this study was to assess the influence of a municipal solid waste compost (MSWC) on the mobility, bioaccessibility and toxicity of several potentially toxic elements (PTE), i.e. Pb (15,383 mg kg-1), Zn (4076 mg kg-1), Cu (181 mg kg-1), Sb (109 mg kg-1), Cd (67 mg kg-1) and As (49 mg kg-1), present in a contaminated sub-acidic soil (pH = 5.93). The addition of MSWC at 2 and 4% rates significantly decreased the labile fractions of PTE (with the exception of Cu and As) and at the same time increased the residual fractions of Zn and Sb. In-vitro tests also showed that compost amendment was able to decrease Cd and Cu gastric bioaccessibility, with respect to untreated soil (-19 and 13% of Cd and Cu in MSWC-4% respectively), while a significant increase of As intestinal bioaccessibility was recorded. This increment was attributed to the pH rise (up to 7.0) during the in-vitro intestinal phase, which likely favoured a release of the arsenic non-specifically bonded to MSWC. Soil enzyme activities, i.e. dehydrogenase and β-glucosidase, were significantly enhanced in MSWC-amended soils (i.e. up to ~6.0 and 1.4 times higher in MSWC-4% than in control soil, respectively), as well as soil basal respiration, and the potential metabolic activity and catabolic versatility of soil microbial communities (as assessed by the Biolog ecoplate community level physiological profile). Overall, the results obtained suggested that MSWC, particularly at 4% rate, could be useful to stabilise PTE in sub-acidic contaminated soils and to increase the microbial activity and functionality in these latter soils.
... In contrast, the presence of a substrate in heterogenous nucleation can lower the energy barrier by facilitating the formation of bonds with molecules in the nucleus, which leads to faster nucleation [16]. In addition, heterogeneously nucleated Ca-As phases are typically immobilized on the substrate, whereas the homogeneously nucleated phases remain suspended in the solution and are transported with the fluid before deposition, resulting in an increase in As-mobility [17]. ...
... Natural organic matter (NOM) is ubiquitous in soil and water environments and influences Ca-As heterogeneous nucleation [17,18]. Previous bulk studies demonstrated that NOM forms complexes with Ca 2+ and H n AsO 4 (3Àn)À (where n depends on the local pH, see Fig. S1) [19][20][21]. ...
Heterogeneous nucleation induced by natural organic matter (NOM) can lower the energy barrier for calcium arsenate (Ca-As) precipitation, which aids in immobilizing arsenate (AsⅤ). However, it remains unclear how certain chemical functionalities of NOM affect Ca-As nucleation at the molecular scale. By analyzing changes in the local supersaturation and/or interfacial energy, the present work investigates the Ca-As heterogeneous nucleation kinetics and mechanisms on functional-group–modified model surfaces.
Mica surfaces modified by functional groups of amine (-NH2), hydroxyl (-OH), or carboxyl (-COOH) through self-assembled monolayers were used to investigate how chemical functionalities affect the Ca-As heterogeneous nucleation, in which the distributions of formation kinetics and size (as measured by the change in particle height) of nucleated Ca-As particles were measured by using in situ atomic force microscopy. In a parallel analysis, a quartz-crystal microbalance with dissipation was used to detect the buildup of Ca²⁺ and/or HAsO4²⁻ ions at the solid-fluid interface. PeakForce quantitative nanomechanical mapping and dynamic force spectroscopy using functional-group–modified tips made it possible to calculate the binding energies holding functional groups to Ca-As particles. Nucleated Ca-As particles were characterized by using Raman spectroscopy and high-resolution transmission electron microscopy.
The results indicate that the height of amorphous Ca-As particles formed on a modified mica surface may be ranked in descending order as –NH2 > –OH > bare mica > –COOH, as determined by the buildup of Ca²⁺ and HAsO4²⁻ ions at the solid-fluid interface and the decrease of interfacial energy due to the functional groups. These nanoscale observations and molecular-scale determinations improve our understanding of the roles played by chemical functionalities on NOM in immobilizing dissolved As through heterogeneous nucleation in soil and water.
... Previously, Cr(VI) reduction in soil was enhanced by modified manure-derived BCs, and the toxicity of Cr(VI) was alleviated via adsorption, immobilization and reduction [28]. HA contains heterogeneous organic molecules with abundant functional groups, and can enhance [30] or decrease [31] the mobility of metals in soil, thus contributing to soil washing or soil immobilization. Furthermore, HA represents a significant reservoir of electron donors and thus participates in reduction of Cr(VI) [32]. ...
... As is a type of soluble organic molecule with low pH, HA generally enhances the bioavailability and mobility of heavy metals in soil [30,46,47]. As expected, HA decreased soil pH, but resulted in higher available Cr and Fe concentrations in soil when applied in combination, as opposed to the nZVI alone (Figure 2), indicating that the HA-induced decrease in Cr(VI) was mainly from reduction of Cr(VI) to Cr(III) [32]. ...
Nano-scale zero-valent iron (nZVI) is among the most common nanoparticles widely used for the treatment of various environmental contaminants. However, little is known about the combined effects of nano-zero-valent iron (nZVI) and other soil amendments on soil remediation and plant performance. For the first time, we studied the remediation of Cr(VI)-contaminated soil using bare nZVI (B-nZVI) and starch-supported nZVI (S-nZVI) in combination with either biochar (BC) or humic acid (HA), and the consequent effects on plant growth and Cr accumulation. Both S-nZVI and B-nZVI decreased the contents of Cr(VI) and available Cr in soil, but increased available Fe content, with S-nZVI generally showing more pronounced effects at a higher dose (1000 mg/kg). B-nZVI exerted no inhibition and even stimulation on plant growth, but 1000 mg/kg S-nZVI produced significant phytotoxicity, resulting in decreased plant growth, low chlorophyll content in leaves, and excessive accumulation of Fe in roots. Each nZVI decreased shoot and root Cr concentrations. BC and HA produced synergistic effects with nZVI on Cr(VI) removal from soil, but HA decreased soil pH and increased the availability of Cr and Fe, implying a potential environmental risk. Addition of BC or HA did not alter the effects of either nZVI on plant growth. In conclusion, combined application of 100 mg/kg nZVI and BC could be an ideal strategy for the remediation of soil contaminated with Cr(VI), whereas high-dose S-nZVI and HA are not recommended in the remediation of agricultural soils for crop production or in the phytostabilization of Cr(VI).
... However, the bioavailable fractions of As and Sb were not reduced with respect to the initial polluted soil, neither in the Technosols nor in the underlying soils. This is possibly related to the formation of organic-metallic complexes, which could lead to an increase in the availability of these elements when the pH rises [58,62]. ...
This study evaluated the effectiveness of six Technosols designed for the remediation of polluted soils (PS) by metal(loid)s at physicochemical, biological, and ecotoxicological levels and at a microcosm scale. Technosols T1-T6 were prepared by combining PS with a mix of organic and inorganic wastes from mining, urban, and agro-industrial activities. After two months of surface application of Technosols on polluted soils, we analysed the soil properties, metal(loid) concentration in total, soluble and bioavailable fractions, soil enzymatic activities, and the growth responses of Trifolium campestre and Lactuca sativa in both the Technosols and the underlying polluted soils. All Technosols improved the unfavourable conditions of polluted soils by neutralising acidity, increasing the OC, reducing the mobility of most metal(loid)s, and stimulating both the soil enzymatic activities and growths of T. campestre and L. sativa. The origin of organic waste used in the Technosols strongly conditioned the changes induced in the polluted soils; in this sense, the Technosols composed of pruning and gardening vermicompost (T3 and T6) showed greater reductions in toxicity and plant growth than the other Technosols composed with different organic wastes. Thus, these Technosols constitute a potential solution for the remediation of persistent polluted soils that should be applied in large-scale and long-term interventions to reinforce their feasibility as a cost-effective ecotechnology.
... An increase in external Tl(I) ions also promoted the formation of Tl(I)-carboxyl complexes. In comparison, phenolic hydroxyl groups were expected to be mainly deprotonated at pH 9 (Jayalath et al., 2018;Neale et al., 2009;Su et al., 2021;Wang and Mulligan, 2009). In previous studies, mainly the Tl(I) complexation ability of phenolic hydroxyl groups on HA in neutral to basic environments was demonstrated (Martin et al., 2020;Ruiz-García et al., 2022): phenolic hydroxyl sites have high affinity and availability in neutral and basic environments and may become the leading Tl(I) complexing group on HA. ...
Widely distributed soil humic acid (HA) would significantly affect the environmental migration behavior of Tl(I), but a quantitative and mechanistic understanding of the dynamic Tl(I) retention process on HA is limited. A unified kinetic model was established by coupling the humic ion-binding model with a stirred-flow kinetic model, which quantified the complexation constants and responsiveness coefficients during dynamic Tl(I)-HA complexation. Furthermore, the heterogeneous complexation mechanism of HA and Tl(I) was revealed by batch adsorption experiments, stirred-flow migration experiments, and 2D-FTIR-COS analysis. An increase in pH significantly improved the responsiveness of HA organic binding sites, promoting Tl(I) dynamic retention. Monodentate carboxyl groups induced rapid Tl(I) complexation (kd = 1.9 min-1) in strongly acidic environments. Under weakly acidic conditions, Tl(I) retention on HA was mainly attributed to the synergistic complexation effect of carboxyl and amide groups. Among the groups, multidentate carboxyl-phenolic hydroxyl sites could achieve sustained Tl(I) retention due to their stable complexing properties (logK = 4.48∼7.46) and slow response (kd = 1.1 × 10-3 min-1). These findings are crucial for a comprehensive understanding of the environmental interactions of Tl(I) with humic substances in swamp environments.
... Moreover, complexation reactions by HS hinders the precipitation of soil minerals, such as iron and aluminum [15][16][17][18]. Previous studies also claimed that HS could form complexes with soil minerals (including toxic metals), hydroxides, and organic compounds [19][20][21][22]. However, the sources of natural HS are limited. ...
Humic substances (HS) are originated from naturally decaying biomass. The main products of HS are humic acids, fulvic acids, and humins. HS are extracted from natural origins (e.g., coals, lignite, forest, and river sediments). However, the production of HS from these resources is not environmentally friendly, potentially impacting ecological systems. Earlier theories claimed that the HS might be transformed from lignin by enzymatic or aerobic oxidation. On the other hand, lignin is a by-product of pulp and paper production processes and is available commercially. However, it is still under-utilized. To address the challenges of producing environmentally friendly HS and accommodating lignin in valorized processes, the production of lignin-derived HS has attracted attention. Currently, several chemical modification pathways can be followed to convert lignin into HS-like materials, such as alkaline aerobic oxidation, alkaline oxidative digestion, and oxidative ammonolysis of lignin. This review paper discusses the fundamental aspects of lignin transformation to HS comprehensively. The applications of natural HS and lignin-derived HS in various fields, such as soil enrichment, fertilizers, wastewater treatment, water decontamination, and medicines, were comprehensively discussed. Furthermore, the current challenges associated with the production and use of HS from lignin were described.
... HAs are the most reactive compounds in soil, having the capacity for various chemical and physical reactions in the environment. HAs have a complex structure containing active functional groups, such as carboxyl and hydroxyl, having an important impact on the transformation and migration of metal and metalloids in soil (Wang and Mulligan, 2009;Liu et al., 2020). Thus, toxic metalloid arsenic interacts with HAs and forms As-HA complexes, further influencing As adsorption on the mineral solid phase surfaces, its solubility and mobility (Qian et al., 2022). ...
The arsenite-humic acid binding process was investigated using Isothermal Titration Calorimetry (ITC), Dynamic Light Scattering and Laser Doppler Electrophoresis techniques. The ITC data were successfully (R2 = 0.996-0.936) interpreted by applying the MNIS model, enabling thermodynamic parameters to be determined. The MNIS model was adjusted to the arsenite-HA binding process assuming that hydrogen bonding is the dominant type of interaction in the system. Negative enthalpy change values indicated the arsenite-HAs binding as an exothermic process. Negative ΔG values (-(26.83-27.00) kJ mol-1) pointed out to spontaneous binding reaction, leading to the formation of the arsenite-HA complexes. The binding constant values ((7.57-5.02) 105 M-1) clearly demonstrate pronounced binding affinity. As ΔS values are obviously positive but close to zero, and ΔH>ΔS, the reaction can be considered enthalpy driven. Reaction heats and ΔH values (-(18.96-15.64) kJ mol-1) confirmed hydrogen bonds as the most ascendant interaction type in the arsenite-HA complex. Negative zeta potential values (-45 to -20 mV) had shown that arsenite-HA aggregates remained negatively charged in the whole molar charge ratio range. The HAs' aggregate size change is evident but not particularly pronounced (Zav = 50-180 nm). It can be speculated that aggregation during the titration process is not expressive due to repulsive forces between negatively charged arsenite-HA particles. Thermodynamic and reaction parameters clearly indicated that arsenite-HA complexes are formed at common soil pH values, confirming the possible influence of humic acids on increased As mobility and its reduced bioavailability.
... The benefits of HA on phytoremediation have already been confirmed for arsenic (Wang and Mulligan 2009), cadmium, and copper . Data on the influence of Pb phytoremediation is scarce, but some studies suggest the reverse influence (Yang et al. 2013). ...
Assisted phytoremediation is extremely promising, but is still in development and needs further study. Therefore, the combination use of Erythrostemon gilliesii and humic acid was studied to aid the efficiency of lead nitrate Pb(NO 3) 2 phytoextraction. Seedlings were exposed to five simultaneous treatments of Pb(NO 3) 2 (0, 100, 300, 500, and 700 mg L À1) and humic acid (0 and 300 mg L À1) for three growth months (90 days in summer) and their effects on physiological and morphological traits of plants were recorded. Up to 300 mg L À1 , Pb treatments showed apparent positive (stimulative) effects on plant traits, including dry and fresh weight, length, number of leaves, the diameter of collar and root, and root germination. Lead treatments higher than 300 mg L À1 showed negative (repressive) effects on plant growth. A decrease in Pb uptake was observed in simultaneous treatments of humic acid and Pb, which means more Pb remains unabsorbed in the soil. We conclude that E. gilliesii is well-suited to the phytoextraction of Pb in contaminated areas, but humid acid significantly reduces the efficiency of remediation; therefore, the levels of humic acid should be controlled during the remediation process in an area.
... Sample S3 was black soil, arguably the best type of agricultural soil in China, which was characterised by abundant organic matter, especially humic acids (see Table 1). Wang and Mulligan (2009) found that humic acids could mobilise As in contaminated soil through mechanisms like electrostatic interaction, competitive adsorption and complexation. These might account for the highest As-RBA in sample S3 observed in this study. ...
Arsenic (As) mobilisation assists in remediating As-contaminated soils but might increase ecological and health risks. In this study, risks of applying two mobilising agents were assessed, i.e. an emerging reducing-chelating composite agent [dithionite (Na2S2O4)–EDTA] and a classical low-molecular-weight organic acid (LMWOA) [citric acid (C6H8O7)]. Results showed that both agents induced sharp increase in leachability-based ecological risk of As. Interestingly, the two agents had opposite performances regarding health risks. Na2S2O4–EDTA significantly increased As relative bioavailability (RBA) to 1.83 times that in controls based on in vivo mouse model, and As bioaccessibility to 1.96, 1.65 and 1.20 times in gastric, small intestinal and colon phases based on in vitro PBET-SHIME model. Besides, it caused significant increase of highly toxic As(Ⅲ) in colon fluid. In contrast, C6H8O7 significantly reduced RBA and bioaccessibility of soil As in colon by 44.44% and 14.65%, respectively. Importantly, C6H8O7 restrained bioaccessible As(V) reduction and promoted bioaccessible As(Ⅲ) methylation, further reducing health risk. The phenomena could mainly be attributed to excessive metal components release from soil by C6H8O7 and gut microbiota metabolism of C6H8O7. In summary, C6H8O7 and similar LMWOAs are recommended. The study contributes to mobilising agent selection and development and provides a reference for managing remediation sites.
... carboxyl groups) eventually leading to an increase of stable (i.e. inner sphere) PTE complexes (Wang and Mulligan, 2009); ii) the formation of PTE precipitates in the form of metal oxides or hydroxides. Nevertheless, some studies reported an increase of water soluble and exchangeable Zn and Cd (e.g. ...
... For these reasons, two main types of investigations are carried out when assessing slag weathering processes. These include: i) experiments investigating the influence of the pH of the fluid phase in contact with the slag Cappuyns and Swennen, 2008;Ettler et al., 2004Ettler et al., , 2002Ettler and Johan, 2014;Jarošíková et al., 2017;Kierczak et al., 2013;Kucha et al., 1996;Lidelöw et al., 2017;Navarro et al., 2008;Tyszka et al., 2014;Vanaecker et al., 2014) and ii) experiments evaluating the interaction of the slags with the vegetation cover (Bunzl et al., 2001;Cabala and Teper, 2007;Pistelli et al., 2017;Potysz et al., 2019;Wang and Mulligan, 2009). ...
The long-lasting mining and smelting activity that took place in southern Tuscany since the 1st millennium BCE has left several remains of metallurgical interest, along with metallurgical slags. Over the centuries, these materials were treated as wastes and dumped close to the industrial sites, with no specific disposal or confinement from the surrounding environment. We performed leaching experiments on slag samples from two selected sites, applying conditions to test the effects of various pH conditions, as well as their behavior following the addition of organic acids to simulate a rhizospheric environment. The samples, a crystalline Pb slag and a glass-rich Cu slag, showed a different leachability depending upon their physical and mineral-chemical characteristics, such as the size of the fragments used in the experiments, the mineralogical composition, and the bulk content of metals in the samples. The crystalline Pb slag showed a higher susceptibility to leaching (e.g., 31 % Cu and 65 % Zn) under acidic inorganic conditions, compared to the glass-rich Cu slag, which was prone to organic mediated dissolution (14 % Cu and 6 % Zn). The highest metal mobilization occurred during the pH-dependent leaching experiments at pH 1, reaching 92 % (of leached Pb) and 65 % (Zn) for lead slag and copper slag, respectively.
... The application of humic substances to mine tailings significantly decreased Cu leaching, due to the formation of organomineral complexes [39,11]. Wang and Mulligan reported that humic acid could enhance the mobilization of arsenic and heavy metals from the mine tailings under alkaline conditions (pH 11) [40]. ...
An interdisciplinary study was conducted on the effect of application of plant growth-promoting bacteria and humic acids in the reclamation of acid-generating mining wastes through a vegetation cover. The drainage water from the mining waste was characterized by a pH of 3.58 and high concentrations of sulfate, copper, manganese, and zinc. Strains of the Bacillus and Pseudomonas genera and humic substances produced by biotransformation from lignite were applied. The usage of plant growth-promoting bacteria and humic acid in the reclamation of acid-generating mining wastes produced several beneficial effects. The combined application resulted in a significant decrease in Cu, Fe, Zn and sulfate concentrations in a variety of drainage water samples, due to the suppression of pyrite oxidation. Both plant growth-promoting bacteria and humic acid improve plant growth, when used separately. The highest yield of fresh (between 22% and 43 %) and dry biomass of plants (between 31% and 41 %) was observed after combining both treatments, but the effect depended strongly on the dose of application. Yields of fresh and dry biomass in the combined application increased by treating plants with 0.42 g/kg humic acids, but decreased significantly when applying humic acids in a concentration of 0.84 g/kg soil. The treatment with a microbial consortium and humic substances enhanced significantly the uptake of nitrogen, phosphorus, and potassium by the plants. Furthermore, the addition of Bacillus and Pseudomonas bacteria in combination with humic acids to poor soil for reclamation reduced the Cu and Zn uptake.
... Although revegetation is desirable, mine tailing sites are very unfavorable environments for plants because of poor soil structure (Grandlic et al., 2008), low water holding capacity (Noyd et al., 1995), nutrient deficiencies (Mendez et al., 2007), small numbers of soil microorganisms (Mendez and Maier, 2008b), high heavy metal concentrations (Wang and Mulligan, 2009), and other adverse factors. The toxic effects of high REE concentrations inhibit primary root elongation and decrease plant dry weight and the content of mineral nutrients (Hu et al., 2002). ...
... As sulfide-rich waste materials, pyrite tailings can be oxidized in the presence of air and water (Garcia et al., 2005) spontaneously, which causes acid mine drainage (AMD) consequently (Malmström et al., 2006). AMD is considered as a serious and persistent environmental problem, which leads to the environment acidification and also releasing of significant amounts of various toxic metals into surface and groundwater (Heikkinen and Räisänen, 2009;Wang and Mulligan, 2009;Sahoo et al., 2013;Carvalho et al., 2014). Thus, the control of the pyrite tailings sourced pollution has become an important issue in the past decades, and various methods have been reported (Ouyang et al., 2015;Park et al., 2019;Dong et al., 2020a). ...
The large amount of untreated pyrite tailings has caused serious environmental problems, and the recycling of pyrite tailings is considered as an attractive strategy. Here, we reported a novel non-sintered ceramsite prepared with pyrite tailings (PTNC) as the main active raw material for phosphorus control, and the dosage effect of ingredients on total phosphorus (TP) removal ability was investigated. The results from Plackett-Burman Design (PBD) suggested the dosages of dehydrated sludge, sodium bicarbonate, and cement were the factors which significantly affect the TP removal ability. The Box-Behnken Design (BBD) based response surface methodology was further employed, and it indicated the interactions between different factors, and the optimized recipe for PTNC was 84.5 g (pyrite tailings), 10 g (cement), 1 g (calcined lime), 1 g (anhydrous gypsum), 3 g (dehydrated sludge), and 0.5 g (sodium bicarbonate). The optimized PTNC was characterized and which presented much higher specific area (7.21 m²/g) than the standard limitation (0.5 m²/g), as well as a lower wear rate (2.08%) rather than 6%. Additionally, the leaching metal concentrations of PTNC were far below the limitation of Chinese National Standard. The adsorption behavior of TP on PTNC was subsequently investigated with batch and dynamic experiments. It was found that the calculated max adsorption amount (qmax) was about 7 mg/g, and PTNC was able to offer a stable TP removal ability under different hydraulic retention time (HRT). The adsorption mechanism was discussed by model fitting analysis combined with XRD and SEM characterization, and cobalt phosphide sulfide was observed as the newly formed substance through the adsorption process, which suggested the existing of both physical and chemical adsorption effect. Our research not only offered an economic preparation method of ceramsite, but also broadened the recycling pathway of pyrite tailings.
... Metals were removed to a somewhat larger extent from the Fenton-treated sediments compared to the electrochemically treated sediments. This is probably due to the low pH (~ 2.0-3.2) in the Fenton process (Gambrell et al., 1991;Zang et al., 2017) causing a metal release in the leachates, but it may also be explained by the degradation of organic matter in the sediments (Kalmykova et al., 2008;Wang and Mulligan, 2009;Mecozzi et al., 2011). Metals (e.g., Cu and Cd) bound to humic acids and other organic acids in sediments through complexation are released if the acids are degraded during the oxidation or protonated due to the low pH. ...
Metal and tributyltin (TBT) contaminated sediments are problematic for sediment managers and the environment. This study is the first to compare Fenton’s reagent and electrochemical treatment as remediation methods for the removal of TBT and metals using laboratory-scale experiments on contaminated dredged sediment. The costs and the applicability of the developed methods were also compared and discussed. Both methods removed > 98% TBT from TBT-spiked sediment samples, while Fenton’s reagent removed 64% of the TBT and electrolysis 58% of the TBT from non-spiked samples. TBT in water phase was effectively degraded in both experiments on spiked water and in leachates during the treatment of the sediment. Positive correlations were observed between TBT removal and the added amount of hydrogen peroxide and current density. Both methods removed metals from the sediment, but Fenton’s reagent was identified as the most potent option for effective removal of both metals and TBT, especially from highly metal-contaminated sediment. However, due to risks associated with the required chemicals and low pH level in the sediment residue following the Fenton treatment, electrochemical treatment could be a more sustainable option for treating larger quantities of contaminated sediment.
... Arsenic (As) is a toxic metal that causes great harm to both the ecosystem and human health (Wang and Mulligan 2009). As is present in high concentrations in tailing soil and easily accumulates in both soil and groundwater by various means. ...
PurposeIncreasing the migration of arsenic in contaminated soil is an important topic in the field of soil remediation. The purpose of this study was to investigate the enhancement of arsenic migration in soil by low molecular weight organic acids.Materials and methodsFour different low molecular weight organic acids were used to wash the soil to increase arsenic mobility under different experimental conditions, including the type of LMWOA, reaction time, and pH. The arsenic fractions in the soil were further quantitated and analyzed.Results and discussionIn the batch experiment, the LMWOA enhancement of arsenic migration was in the order of 3-mercaptopropionic acid > aspartic acid > succinic acid > propionic acid. At pH 11, 247.29 mg/kg arsenic was leached from the soil with 3-mercaptopropionic acid over 48 h. This was confirmed in column experiments where 3-mercaptopropionic acid was also the most effective, releasing 21.02% of the arsenic after 75 h. This suggests that the sulfhydryl group of 3-mercaptopropionic acid was superior to other groups in accelerating arsenic migration.Conclusions
These results enhance our understanding of the interaction between arsenic migration and organic acid functional groups and have applications for the development of soil remediation technology.
... Bacterial leaching of metals from mineral resources has several advantages, including simple process, prevention of hazardous acid wastes, low investment, and less harmful to the environment than classical ore processing techniques (Ahmadi et al., 2015;Noei et al., 2017;Rawlings et al., 2003). Several studies have been carried out on the removal of heavy metals such as Zinc (Zn), Arsenic (As), Copper (Cu), and Iron (Fe) from ore deposits (Razo et al., 2004;Wang & Mulligan., 2009;Nguyen et al., 2015). Zn is the fourth most commonly used metal in the world, behind iron, aluminum, and copper (Home | ZINC. ...
Today, various methods such as bioleaching are increasingly used to remove toxic and reuse useful metals from low-grade ores and tailings. Bioleaching is an ecologically based technique carried by iron or sulfur-oxidizing bacteria, which convert insoluble metal sulfide to soluble metal sulfate. The purpose of this study was to test and compare two different methods, including Flask and Column experiments, to remove Zinc, Copper, Arsenic, and Iron. The materials were the same in both tests; inoculum came from the tailings of Neves-Corvo Mine, and the mineral sample was collected from Panasqueira Wolfram-Tin mine. Firstly, the cultures were tested for metal resistance and adapted by 3-day transference, adding sodium thiosulfate as an energy source supplement. Secondly, bioleaching tests were conducted in Flasks and Columns in 35 and 30 days, respectively. Finally, samples were taken to evaluate particle size, chemical compositions, bacterial growth, pH, oxidation–reduction potential (ORP), sulfate concentration, and metal content in the leachate. Besides, the Scanning Electron Microscope (SEM) pictures proved the existence of bacterial cells during the bioleaching tests. The results indicated that the Flask tests were superior to Column experiments in removing Zinc, Arsenic, and Copper from the mineral ore samples. However, Column experiments showed better results in the recovery of Iron in comparison with Flask tests.
... 2010).Wang and Mulligan (2009) reported that humic acid could enhance the mobilization of arsenic and heavy metals from the mine tailings under alkaline conditions (pH 11). The origin and composition of humic substances, the dose of application, pH, metal concentration and speciation in mining waste are important factors that need to be taken into account in reclamation technologies.Metal-mineral-microbe interactions have also been the subject of a number of studies (Gadd 2010; Kong and Glick 2017). ...
Generation of acidic mine drainage is a major environmental problem in areas with mining waste. The cost-effective method for reclaiming of acid-generating mining wastes is a vegetation cover. Using plant growth-promoting bacteria (PGPR) and humic acid in remediation have several beneficial effects. The application of both humic substances and PGPR resulted in a decrease in Cu, Fe, Zn and sulfate concentrations in a variety of drainage water samples. Both PGPR and humic acid improve plant growth when used separately, however, the combination of both treatments has the most positive effect on fresh biomass yield – between 22% and 43 % and dry biomass of plants – between 31% and 41 %. Furthermore, addition of Bacillus and Pseudomonas bacteria, in combination with humic acids, to poor soil for reclamation improved grass mineral nutrition and reduced Cu and Zn uptake. The treatment with PGPR and humic acids significantly increased the uptake of nitrogen, phosphorus and potassium by plants.
... Some of these unstable materials are pyrite, arsenopyrite and other sulphides which can be easily oxidized once exposed to air and water (Warhurst and Noronha, 2000;Fan et al., 2016). The oxidation of these sulphides will produce metal laden acid which can be mobilised into the geoenvironment (Wang and Mulligan, 2009;Heikkinen and Raisanen, 2009;Carvalho et al., 2014). ...
This study was carried out on leaching of tailings at 30 ᵒC and 40 ᵒC. The mineralogical and chemical composition of the tailings material were determined by Quantitative X-Ray Diffractometry (QXRD) and Scanning Electron Microscopy combined with Energy Dispersive Spectroscopy (SEM-EDAX). The study revealed that the tailings contain sulphides (arsenopyrite and pyrite) which can leach to produce arsenic (As) and other ions in solution. The acid released during leaching depends on the temperature of leaching. More acid was produced at higher temperature (40 ᵒC) than lower temperature (30 ᵒC). It was established that arsenic precipitation from solution was higher at higher temperature (40 ᵒC) than lower temperature (30 ᵒC). Mimicking the study in a typical tailings environment, it could be proposed that As mobilisation will be enhanced at lower temperature (30 ᵒC) than at higher temperature (40 ᵒC). Keywords: Tailings, Leaching, Arsenopyrite, Heavy metals and Temperature
... Although humic acid-bound As was about 50% of soil total As. The humic acid-bound fraction only contributed 9.93% to rice As, which may be resulted from As sorption and mobilization by humic acid in soil (Thanabalasingam & Pickering, 1986;Wang & Mulligan, 2009). Except for Hg, the geochemical behaviour of Fe/Mn oxyhydroxides on metals accumulation in rice was explained by PC1 in all PCA analyses, indicating that soil redox change could be a main factor of geochemical activity of soil metals (Bourg & Loch, 1995). ...
This study developed a method to build relationships between chemical fractionations of heavy metals in soils and their accumulations in rice and estimate the respective contribution of each geochemical speciation in the soils from the Yangtze River Delta, China. In contaminated areas, residue and humic acid-bound fractions in soils were the main phases for most heavy metals. The mobility of heavy metals was in this following order: Cd > Pb ≈ Zn > Ni > As ≈ Cr > Hg. Transfer factors calculated by the ratios of specific fractionations of heavy metals in the soil–rice system were used to assess the capability of different metal speciation transfer from soil to rice. The carbonate and Fe/Mn oxyhydroxides bound phase had significant positive correlations with total metal concentrations in rice. Hg uptake by rice might be related to the exchangeable and carbonate-bound fractions of soil Hg. Results of PCA analysis of transfer factors estimated that the labile fractions (i.e. water soluble, exchangeable and carbonate bound) contributed more than 40% of the heavy metal accumulations in rice. Effect of organic matter and residue fraction on metals transfer was estimated to be ~ 25 to ~ 30% while contribution of humic acid and Fe/Mn oxyhydroxides-bound fractions was estimated to be ~ 20 to ~ 30%. Modified risk assessment code (mRAC) and ecological contamination index (ECI) confirmed that the soil samples were polluted by heavy metals. Soil Cd contributed more than 80% of mRAC. Contrarily, the main contributors to ECI were identified as As, Hg, Pb and Zn. The average values of total target hazard quotient (TTHQ) and Risktotal were above 1 and 10–4 respectively, implying people living in the study area were exposed to both non-carcinogenic and carcinogenic risk. As and Pb were the main contributor to high TTHQ value while As, Cd and Cr in rice contributed mostly to Risktotal value. Spatial changes of ecological risk indexes and human health risk indexes showed that the samples with high TTHQ values distributed in the area with high values of mRAC. Likewise, the area with high ECI values and with high carcinogenic risk overlapped.
... carboxyl groups) eventually leading to an increase of stable (i.e. inner sphere) PTE complexes (Wang and Mulligan, 2009); ii) the formation of PTE precipitates in the form of metal oxides or hydroxides. Neverthless, some studies reported an increase of water soluble and exchangeable Zn and Cd (e.g. ...
Highlights
- Water Treatment Residuals, Red Muds, Municipal Solid Waste Compost and Biochar can reduce labile PTE in contaminated soils.
- When used as amendments, WTR, RM, MSWC and BCH improve soil chemical fertility of PTE-polluted soils.
- WTR, RM, MSWC and BCH stimulate soil enzyme activity and heterotrophic bacterial abundance in PTE-polluted soils.
- WTR, RM, MSWC and BCH can be used as strategic amendments to enhance plant growth in environments polluted by PTE.
Potentially toxic elements (PTE), e.g. As, Sb, Cd, Cu, Pb, Zn, can severely impact soil element cycling, organic matter turnover and soil inhabiting microbiota. Very often this has dramatic consequences for plant growth and yield which are greatly restricted in PTE-contaminated soils. The use of innovative amendments to reduce the labile pool of such soil contaminants, can result as a feasible and sustainable strategy to improve the fertility and functionality of PTE-contaminated soils as well as to exploit these latter from an agronomic point of view. Water treatment residuals (WTR), red muds (RM), organic-based materials originating from the waste cycle, e.g. municipal solid waste compost (MSWC) and biochar (BCH), have emerged in the last decades as promising amendments. In this paper, we report a synthesis of the lessons learned from research carried out in the last 20 years on the use of the above-mentioned innovative amendments for the manipulation of soil fertility and functionality in PTE-contaminated soils. The amendments considered possess physico-chemical properties useful to reduce labile PTE in soil (e.g. alkaline pH, porosity, Fe/Al phases, specific functional groups and ionic composition among the others). In addition, they contain organic and inorganic nutrients which can contribute to improve the soil chemical, microbial and biochemical status. This is often reflected by a higher organic matter content in amended soils and/or an increase of the cation exchange capacity, available P and total N and/or dissolved organic C. As a result, soil microbial abundance, in particular heterotrophic fungi and bacteria, and enzyme activities (e.g. dehydrogenase, urease and β-glucosidase) are commonly enhanced in amended soils, while plant growth can be significantly stimulated. Overall, the obtained results suggest that the studied amendments can be used to reduce PTE bioavailability in polluted soils, improve soil microbial status and functionality, and enhance the productivity of different crops. This can offer a precious opportunity for the productive recovery of PTE-polluted soils.
... It was found that the presence of humic acid promoted the formation of a humic acid iron water complex and prevented the formation of iron hydroxide, thus increasing the availability and mobility of As in the tailings. 36 4.3. Effects of amendments on the speciation distribution of Cd, Zn, Cu and As ...
This study aims to assess the effect of green waste compost (GWC), biochar (BC) and humic acid (HA) amendments of an alkaline heavy metal-contaminated soil. In this study, amendments with GWC, GWC + BC and GWC + HA were applied to the heavy metal-contaminated soil in four application rates (0, 1, 2 and 5%), and was aimed at substantially mitigating the bioavailability of heavy metals for pakchoi cabbage from the sewage irrigation soils. The addition of different ratios of amendments can increase the pH of the soil by 0.11–0.30 units and also increase the organic matter content by 3.1–35.1%. The concentration of available arsenic (As), cadmium (Cd), zinc (Zn) and copper (Cu) in the CaCl2 extract was decreased effectively by all the amendments, except for the increase in the available concentration of As by compost–humic acid (T8) in the soil. Compared with the control, the CaCl2 extractable Cd was decreased by 33–48% after the addition of different ratios of amendments in the soil. Moreover, by increasing the content of compost and compost–biochar in combinations, easily exchangeable fractions of As, Cd, Zn and Cu were decreased, while the oxidation fraction and residual fractions were increased. When the soil amendments were applied, fresh weight of the root and shoot increased by 29–63% and 39–85%, respectively. Cd concentration in the roots and shoots of the pakchoi cabbage decreased by 21–44% and 26–53%, respectively, after adding different ratios of amendments. All the amendments were effective in reducing the Cd, Zn and Cu uptake by the roots and shoots of the pakchoi cabbage, and simultaneously reduce the absorption of As in the roots of pakchoi cabbage. As soil amendments, GWC alone or GWC + BC/GWC + HA application can significantly reduce the heavy metal levels in pakchoi cabbage while increasing the biomass production and higher application rate is more effective than the lower application rate.
... Nevertheless, humic biosurfactants are reported to efficiently mobilize labile, exchangeable, and complexed HM due to their large complexing capacities (Halim et al. 2003;Garcia-Mina 2006). The supramolecular conformation of HA coupled to their negatively charged acidic functional groups were shown to improve the mobilization of As, as arsenate [As(V)], and other metals such as Zn, Pb, and Cu from a mine tailings by soil flushing with HA, which also reduce metal precipitation (Wang and Mulligan 2009). A humic acid from sewage sludge compost at a concentration of 3000 mg of C L −1 was used to wash a sandy soil artificially spiked with 1984 mg kg −1 of Cu and 50 mg kg −1 of Cd and found to remove by a single washing 80.7% of Cu and 69.1% of Cd (Kulikowska et al. 2015). ...
We evaluated the effectiveness of natural organic surfactants such as humic acids (HA) from lignite to simultaneously wash heavy metals (HM) and polychlorobiphenyls (PCB) from a heavily contaminated industrial soil of northern Italy. Supramolecular HA promote in solution a micelle-like structure, where recalcitrant apolar organic xenobiotics are repartitioned from surfaces of soil particles during soil washing process. Concomitantly, the HA acidic functional groups enable a simultaneous complexation of HM. A single soil washing with HA removed 68 and 75% of PCB congeners for 1:1 and 10:1 solution/soil ratios, respectively. The same HA washing simultaneously and efficiently removed a cumulative average of 47% of total HM, with a maximum of 57 and 67% for Hg and Cu, respectively. We showed that washing a highly polluted soil with HA solution not only is an effective and rapid soil remediation technique but also simultaneously removes both HM and persistent organic pollutants (POP). Soil washing by humic biosurfactants is also a sustainable and eco-friendly technology, since, contrary to synthetic surfactants and solvents used in conventional washing techniques, it preserves soil biodiversity, promotes natural attenuation of unextracted POP, and accelerates further soil reclamation techniques such as bio- or phytoremediation.
... Organotins are likely to sorb to both inorganic and organic colloids, through the formation of complexes (Dubascoux et al., 2008). Humic acid and Fe colloids dissolved in water have also been found to sorb metals through complexation (Fent and Looser, 1995;Lyvén et al., 2003;Kalmykova et al., 2008a;Wang and Mulligan, 2009;Boechat et al., 2016). This means that HA and Fe colloids could potentially extract TBT from sediment into a leachate. ...
All over the world, elevated levels of metals and the toxic compound tributyltin (TBT) and its degradation products are found in sediments, especially close to areas associated with shipping and anthropogenic activities. Ports require regular removal of sediments. As a result, large volumes of often contaminated sediments must be managed.
The aim of this study was to investigate enhanced leaching as a treatment method for organotin (TBT) and metal (Cu and Zn) contaminated marine sediments. Thus, enabling the possibility to reuse these cleaner masses e.g. in construction. In addition to using acid and alkaline leaching agents that extract the OTs and metals but reduce the management options post treatment, innovative alternatives such as EDDS, hydroxypropyl cellulose, humic acid, iron colloids, ultra-pure Milli-Q water, saponified tall oil (“soap”), and NaCl were tested. Organotin removal ranged from 36 to 75%, where the most efficient leaching agent was Milli-Q water, which was also the leaching agent achieving the highest removal rate for TBT (46%), followed by soap (34%). The TBT reduction accomplished by Milli-Q water and soap leaching enabled a change in Swedish sediment classification from the highest class to the second highest class. The highest reduction of Zn was in HPC leached samples (39% removal) and Cu in EDDS leached samples (33% removal). Although high metal and OT leaching were achieved, none of the investigated leaching agents are sufficiently effective for the removal of both metals and OTs. The results of this study indicate that leaching with ultra-clean water, such as Milli-Q water, may be sufficient to treat TBT contaminated sediments and potentially allow mass reuse.
... The variation in soil pH and organic matter is important parameters in affecting the mobility and availability of heavy metals. Mine waste and mine soils have low organic matter content and high acidity which mobilizes heavy metals (Cu, Pb, and Zn) (Arenas-Lago et al. 2014;Wang and Mulligan 2009). Increase in temperature increases the availability of heavy metals in soil and promotes the transfer of Zn and Cd from soil-to-plant system (Cornu et al. 2016). ...
The increasing demand for minerals pressurizing the mining authorities to extract low-grade ore results in more mining waste and degradation of the environment. The main aim of review was to understand the role of climatic factors (temperature, wind, and precipitation) in dispersal and mobility of heavy metals in soil, water, and vegetation in Cu mining region. The major source of contamination in the mining sector is tailings, overburden rocks, and abandoned mines. The contaminates or fine particles of sulfide-rich mining waste follow two major pathways for the dispersal: aerial and leaching. Sulfides on exposure to oxygen and water generate acid mine drainage which results in leaching of heavy metals. The pit water of abandoned mines is also a cause of concern which contaminates the groundwater resources. Climatic factors such as temperature, precipitation, and wind significantly influence the paths of contaminate dispersal. In arid/semi-arid regions, high temperature forms fine-grained efflorescence salts on tailings or exposed surficial mines which are carried away by strong winds/water and contaminates the surroundings. In wet regions, the leaching of heavy metals from both tailings and overburden rocks sulfides results in environmental contamination. The application of impermeable layers is highly recommended. The climatic factors (temperature, wind, and precipitation) significantly control the dispersal and mobility of heavy metals in Cu mining region. The implementation of waste management policies and pollution control technologies is recommended after considering the climatic factors.
... After 20 and 40 days of planting, arsenic was strongly adsorbed in the exchangeable, organic, and residual fractions (Table 4). Adsorption and desorption of arsenic on oxides has been recognized as a mechanism of its mobility control [63][64][65]. In addition, carbon rich sludge is known to increase arsenic solubility [66]. ...
Aim: The use of copper-based preservatives such as chromated copper arsenate (CCA) and creosote to prolong the life of lumber present environmental concerns because they contain heavy metals and polycyclic aromatic hydrocarbons which are toxic to humans. The aim of this study was to investigate the effects of sewage sludge biosolid amendment on the distribution and mobility of chromium, copper and arsenic in chromated copper arsenate contaminated soils subjected to phytoremediation using maize (Zea mays L.).
Place and Duration of the Study: Random composite soil samples from Kitetika wood factory, Wakiso, Uganda and sewage sludge biosolid from National Water and Sewerage Corporation plant in Bugolobi, Kampala, Uganda were collected and prepared. Maize grains were obtained from FICA Seeds Limited (Uganda). The pot experiments and analysis of samples were done at Mbarara University of Science and Technology (Mbarara) and Directorate of Government Analytical Laboratory, Kampala (Uganda), respectively. Methodology: The fresh CCA contaminated soils and sewage sludge biosolid were analyzed for physicochemical parameters and heavy metals (chromium, copper and arsenic). Sewage sludge biosolid was added to 1 kg of the contaminated soils at 5-25% (w/w) in 2 L plastic containers, watered and maintained at 25 ℃ for 14 days to stabilize. Controls were set up with unamended soils. Thereafter, maize was planted in the potted soils for 40 days. The concentrations of the trace metals in the soils were determined after 20 and 40 days of maize growth by atomic absorption spectroscopy. Results: The concentrations of chromium, copper and arsenic in fresh CCA contaminated soils were 365.8 ± 6.18 mg/kg, 109.72 ± 14.04 mg/kg and 28.22 ± 3.8 mg/kg, respectively. Basing on mobility factor, bioavailability of the trace metals followed the chemical sequence copper (8.9%) < chromium (17.1%) < arsenic (30.2%). Conclusion: The maize variety experimented could be used to phytoextract or phytostabilize the trace metals in the CCA contaminated soils without or with 5-25% amendment. Amendment with sewage sludge biosolid improved the phytoremediation potential of maize. Arsenic was the most mobile and bioavailable metal in CCA contaminated soils. Further studies should use other local maize varieties such as Longe series.
... Arsenic is carcinogenic and highly toxic, especially the inorganic forms in water or As(III) and As(V) and most arsenic compounds are odorless and tasteless and so might go undetected. Chronic exposure can lead to various illnesses, including but not limited to, skin, lung, bladder and kidney cancers, anemia, leucopenia, and neurological and cardiovascular disorders (Wang and Mulligan 2009;Jovanović et al. 2011). ...
Natural groundwater from the towns of Wabana and Freshwater and treated well water from the town of Wabana in Newfoundland and Labrador, Canada were tested separately and together in sand columns to study the removal of arsenic. The most ideal conditions for arsenic removal appeared to include an arsenic concentration of approximately 35 µg/L and lower, an Fe:As mass ratio in the order of 65 and lower, and aeration of the sand media. Active aeration by pumping air though the filter, passive aeration by scraping off top layers of sand and virtual aeration by diluting the strength of the water being treated, were employed and compared. For tests where groundwater from the towns of Wabana and Freshwater was combined, arsenic removal was optimized and other elements, in addition to iron, were also correlated with effluent arsenic. Further, for these same tests there was a gradual increase in effluent pH that could have been due to oxygen depletion or gradually more reducing conditions in the sand column. Where Ni, Mn and Zn were correlated with effluent arsenic it was concluded that the increase in pH increased heavy metal removal and arsenic release. In the test where the treated Wabana water made up a greater proportion of the mix than the Wabana groundwater, lithium was also correlated with arsenic.
... Ashworth and Alloway (2008) showed that the solubility of the heavy metals copper (Cu), nickel (Ni), and lead (Pb)in soil have a strong positive relationship to the solubility of organic matter. Soil DOM may increase aqueous heavy metal concentrations by forming metal-DOM aqueous complexes, as demonstrated by Wang and Mulligan (2009). However, Ranville et al. (2007) showed that high DOC levels had no effect on uranium remobilization when the pH was above 7. ...
... For instances, biodegradation of organic diesel in groundwater has been accelerated by making use of the surfactant activity of HS and the increased microbial bioavailability resulting from the presence of HS (Van Stempvoort et al., 2002). The metal-chelating ability of humic acids allows inorganics such as copper and arsenic to enhance their solubility and mobilization capacity (Wang and Mulligan, 2009;Soler-Rovira et al., 2010). The presence of oxygen-or nitrogen-based functional groups combined with aromatic groups that effectively chelate metal ions is regarded as key to inducing efficient remediation of metalcontaminated sites. ...
Humic substances readily identifiable in the environment are involved in several biotic and abiotic reactions affecting carbon turnover, soil fertility, plant nutrition and stimulation, xenobiotic transformation and microbial respiration. Inspired by natural roles of humic substances, several applications of these substances, including crop stimulants, redox mediators, anti-oxidants, human medicines, environmental remediation and fish feeding, have been developed. The annual market for humic substances has grown rapidly for these reasons and due to eco-conscious features, but there is a limited supply of natural coal-related resources such as lignite and leonardite from which humic substances are extracted in bulk. The structural similarity between humic substances and lignin suggests that lignocellulosic refinery resulting in lignin residues as a by-product could be a potential candidate for a bulk source of humic-like substances, but structural differences between the two polymeric materials indicate that additional transformation procedures allowing lignin architecture to fully mimic commercial humic substances are required. In this review, we introduce the emerging concept of artificial humification of lignin-related materials as a promising strategy for lignin valorization. First, the core structural features of humic substances and the relationship between these features and the physicochemical properties, natural functions and versatile applications of the substances are described. In particular, the mechanism by which humic substances stimulate the growth of plants and hence can improve crop productivity is highlighted. Second, top-down and bottom-up transformation pathways for scalable humification of small lignin-derived phenols, technical lignins and lignin-containing plant residues are described in detail. Finally, future directions are suggested for research and development of artificial lignin humification to achieve alternative ways of producing customized analogues of humic substances.
... HSs in soil and water environments play multifunctional roles such as transport and distribution of major macro-and micronutrients to plants and also in the fate and transport of contaminants and pollutants. 8,9 The functions of HSs and their interactions with chemicals depend on the environmental conditions such as pH, 10,11 ionic strength, 12−15 concentration of HSs themselves, 16 temperature, 17 and other physical and chemical parameters of the systems concerned. Some specific physical properties of HSs, especially the size and aggregation, are affected by the abovementioned chemical conditions and surface activity. ...
Aggregation−dispersion, charging, and aggregate strength of Leonardite humic acid (LHA) were investigated in CaCl 2 and MgCl 2 solutions as a function of pH and ionic strength (I). The strength or the withstanding force of aggregates of humic substances (HSs) against breakage is important because this force influences the transport and distribution of pollutants and nutrients along with HSs through the change in the size of HS aggregates as a transport unit. We observed the dominancy of aggregation of LHA at high pH than at low pH in every case of CaCl 2 and MgCl 2 solutions. This observation suggests the higher binding efficiency of these divalent ions at high pH, though there was no obvious relation with electrophoretic mobility and aggregation of LHA. Further, we first revealed the numerical value of the strength of HS aggregates by using a simple experimental setup of aggregate breakup under laminar converging flow through a capillary tube. The obtained values of the strength of LHA aggregates were higher in the presence of CaCl 2 solution than MgCl 2 solution, and the strength increased with pH. The highest strengths of LHA aggregates in 30 mM (I) CaCl 2 and MgCl 2 solutions were around 5.8 and 2.4 nN, respectively, at pH around 9.
... Humic substances are ubiquitous in the environment, occurring in all soils, waters, and sediments of the ecosphere. One of their most striking characteristics is the ability to interact with metal ions, oxides, hydroxides, mineral and organic compounds, including toxic pollutants [22], to form water-soluble and insoluble complexes. Humic acid (HA) has been reported to interfere with the biosorption of heavy metals-Pb(II), Cu(II), Zn(II), Cd(II), and Ni(II), on activated carbon [23]. ...
Uptake of Sr(II) from simulated low level radioactive waste, employing radiotracer ⁸⁵⁺⁸⁹Sr, has been carried out with humic acid by a batch equilibration biosorption study. The process exhibited rapid kinetics and at optimized parameters, Sr(II) was biosorbed from simulated reactor and reprocessing waste by 84 ± 2% and 75 ± 2% respectively. Kinetic modelling revealed that the process follows Ho and McKay’s linear pseudo second order kinetics, indicating chemisorption mechanism of binding. Thermodynamic studies ascertain the exothermic, spontaneous and feasible nature of the process. This work proved the viability of humic acid for Sr(II) removal as an eco-friendly, cost effective alternative to conventional techniques.
... This was probably due to the maximal solubility of As at near-neutral pH (mean of 7.6 ± 0.3) in the presence of OM (Carbonell- Barrachina et al., 2000). Indeed, even at low concentrations (1-20 mg L −1 ), DOM may still influence As mobility and can even increase up to three times the As release in pore water through competition onto sorption sites, formation of soluble complexes, and electrostatic interaction (Redman et al., 2002;Bauer and Blodau, 2006;Wang and Mulligan, 2009;Hwang and Neculita, 2013). In the amended tailings, and at pH 7 to 9, As in the leachates would predominantly be under the form of As(V) as HAsO 4 2− or H 2 AsO 4 − . ...
Peat and mine drainage treatment sludge can be valorized as amendments on mine sites to stabilize gold mine tailings and reduce the potential leaching of contaminants in pore water. However, the influence of organic amendments on the mobility of metalloids and/or metals in the tailings must be validated, as the leached contaminants may vary according to their type, nature, and origin. The objective of the present study was to evaluate over time the effect of peat‐ and/or Fe‐rich sludge amendments on the mobility of As and metallic cations in the drainage water of tailings potentially producing contaminated neutral drainage. Ten duplicated weathering cell experiments containing tailings alone or amended with peat and/or Fe‐rich sludge (5–10% dry weight) were performed and monitored for 112 d. The results showed that as low as 5% peat amendment would promote As mobility in tailings’ pore water, with As concentrations exceeding Quebec discharge criteria (>0.2 mg L⁻¹). In addition, As(III), the most mobile and toxic form, was predominant with 10% peat, whereas organic species were negligible in all cells. The use of peat alone as organic amendment for the stabilization of tailing contaminants could increase the risk of generating As‐rich contaminated neutral drainage. Conversely, the mix of only 5% Fe‐rich sludge with or without peat decreased As concentrations in leachates by 65 to 80%. Further studies on the use of “peat” or “peat + Fe‐rich sludge” as cover or amendment should be conducted with a focus on Fe/As and Ca/As ratios.
Core Ideas
Peat amendments enhanced the leaching of As from gold mine tailings.
Amendments of 5% peat promoted As(V) leaching, whereas 10% peat increased As(III) leaching.
As(III) was predominant at ≥20 mg L⁻¹ dissolved organic C from peat.
Mine drainage treatment sludge could decrease As concentrations by 65 to 80% in tailings’ pore water.
Objectives:The soil around waste mine sites can be contaminated with heavy metals by mine tailings and leachate, and heavy metals can accumulate in the body through crops harvested from contaminated soil. The stabilization method is often applied to the restoration of contaminated soil around abandoned mines, but it is necessary to develop natural stabilizers that are not harmful to the environment. In this study, starfish( Asterina pectinifera ) and cockle shells were evaluated as stabilizers for arsenic and heavy metal(Pb, Zn) contaminated soil.Methods:Starfish and cockle shells were processed into -#10 mesh, -#20 mesh, and calcined (900℃, 2hr) -#10 mesh to evaluate their characteristics through XRD and XRF analyses. The stabilized soil was eluted at 0.1 N HCl. Then the stabilization efficiency was evaluated with ICP-OES analysis, and the stabilization mechanism was identified with SEM-EDX analysis. Afterwards, lettuce was cultivated in the stabilized soil and the concentration of heavy metals transferred from the soil to the lettuce was evaluated.Results and Discussion:The calcination process converts the CaCO<sub>3</sub> in the natural stabilizer into CaO. Arsenic and heavy metals are effectively immobilized within the soil through pozzolanic reactions and Ca-As precipitation. Nitric acid decomposition of lettuce grown in the stabilized soil demonstrated the absence of arsenic, meeting the safety standards outlined in the Korean Food Standard Codex.Conclusion:The stabilization of soil contaminated with arsenic and heavy metals by starfish and cockle shell was confirmed to be attributed to pozzolanic reactions and the formation of insoluble precipitates. In addition, they could be used as natural waste stabilizers based on their high calcium carbonate content.
Anthropogenic and biogenic ligands may mobilize uranium (U) from tetravalent U (U(IV)) phases in the subsurface, especially from labile noncrystalline U(IV). The rate and extent of U(IV) mobilization are affected by geochemical processes. Competing metals and humic substances may play a decisive role in U mobilization by anthropogenic and biogenic ligands. A structurally diverse set of anthropogenic and biogenic ligands was selected for assessing the effect of the aforementioned processes on U mobilization from noncrystalline U(IV), including 2,6-pyridinedicarboxylic acid (DPA), citrate, N,N′-di(2-hydroxybenzyl)ethylene-diamine-N,N′-diacetic acid (HBED), and desferrioxamine B (DFOB). All experiments were performed under anoxic conditions at pH 7.0. The effect of competing metals (Ca, Fe(III), and Zn) on ligand-induced U mobilization depended on the particular metal–ligand combination ranging from nearly complete U mobilization inhibition (e.g., Ca-citrate) to no apparent inhibitory effects or acceleration of U mobilization (e.g., Fe(III)-citrate). Humic substances (Suwannee River humic acid and fulvic acid) were tested across a range of concentrations either separately or combined with the aforementioned ligands. Humic substances alone mobilized appreciable U and also enhanced U mobilization in the presence of anthropogenic or biogenic ligands. These findings illustrate the complex influence of competing metals and humic substances on U mobilization by anthropogenic and biogenic ligands in the environment.
Exposed and un-remediated metal(loid)-bearing mine tailings are susceptible to wind and water erosion that disperses toxic elements into the surrounding environment. Compost-assisted phytostabilization has been successfully applied to legacy tailings as an inexpensive, eco-friendly, and sustainable landscape rehabilitation that provides vegetative cover and subsurface scaffolding to inhibit offsite transport of contaminant laden particles. The possibility of augmented metal(loid) mobility from subsurface redox reactions driven by irrigation and organic amendments is known and arsenic (As) is of particular concern because of its high affinity for adsorption to reducible ferric (oxyhydr)oxide surface sites. However, the biogeochemical transformation of As in mine tailings during multiple redox oscillations has not yet been addressed. In the present study, a redox-stat reactor was used to control oscillations between 7 d oxic and 7 d anoxic half-cycles over a three-month period in mine tailings with and without amendment of compost-derived organic matter (OM) solution. Aqueous and solid phase analyses during and after redox oscillations by mass spectrometry and synchrotron X-ray absorption spectroscopy revealed that soluble OM addition stimulated pyrite oxidation, which resulted in accelerated acidification and increased aqueous sulfate activity. Soluble OM in the reactor solution significantly increased mobilization of As under anoxic half-cycles primarily through reductive dissolution of ferrihydrite. Microbially-mediated As reduction was also observed in compost treatments, which increased partitioning to the aqueous phase due to the lower affinity of As(III) for complexation on ferric surface sites, e.g. ferrihydrite. Oxic half-cycles showed As repartitioned to the solid phase concurrent with precipitation of ferrihydrite and jarosite. Multiple redox oscillations increased the crystallinity of Fe minerals in the Treatment reactors with compost solution due to the reductive dissolution of ferrihydrite and precipitation of jarosite. The release of As from tailings gradually decreased after repeated redox oscillations. The high sulfate, ferrous iron, and hydronium activity promoted the precipitation of jarosite, which sequestered arsenic. Our results indicated that redox oscillations under compost-assisted phytostabilization can promote As release that diminishes over time, which should inform remediation assessment and environmental risk assessment of mine site compost-assisted phytostabilization.
Water pollution by toxic heavy metals poses a threat to the environment and human bodies. Herein, a novel hydrated ferric oxide nanoparticle (HFO) based hybrid adsorbent was fabricated for the removal of toxic Cu(II), Cd(II) and Pb(II) from water. HFOs were immobilized into a porous resin D-201, and then this nanocomposite HFO-D201 was coated with humic acid (HA) to enhance the binding sites of target metals. Both HFOs and HA contribute to the sequestration of heavy metals. The as-synthesized hybrid adsorbent HA-HFO-D201 exhibited excellent performance on the removal of Cu(II), Cd(II), and Pb(II) in a pH range of 3–9, while no Fe leaching was observed. The presence of natural organic matter (20 mg C/L) has limited influences on the adsorption, and more than 85% of the target metals can be removed after treatment. HA-HFO-D201 showed preferable adsorption toward Cu(II) and Pb(II) (1 mg/L) from the background Ca²⁺ solution at much higher concentrations (100 mg/L), while the retention of Cd(II) (1 mg/L) decreased to some extent. Fixed-bed column experiments exhibited that the treatment capacities of HA-HFO-D201 are 90 bed volumes (BV) for Cd(II), 410 BV for Pb(II) and > 800 BV for Cu(II) of simulated contaminated water to meet the WHO drinking water standard. Meanwhile, depleted HA-HFO-D201 can be readily regenerated by a chelating agent Na2EDTA for repeated use. The hybrid adsorbent HA-HFO-D201 has excellent potential to remove heavy metals in water treatment systems.
This article reviews the effect of fungus filaments on the solubility of harmful elements, such as Zn, Cd, Hg, Cr, and As, released from sphalerite, greenockite, cinnabar, chromite, and arsenopyrite minerals, respectively, which are associated with gold mine tailings. Thus, gold mine sites liberate the hazardous elements in different parts of the environment. The fungi’s ability to bioleach Zn, Cd, Hg, Cr, and As elements was investigated, and the method was based on the capacity of microorganisms to extract these harmful elements from solid compounds, such as ZnS, CdS, HgS, FeCr2O4, and FeAsS, which are mostly insoluble. The investigation showed that the filaments of fungi cultivated along gold mine tailing dumps increased the solubility of the harmful elements. Maximum removal of 53% and 62% was observed for As and Zn, respectively, in a leachate of oxalic acid; 100%, 83.2%, and 57% of Cr(VI), Hg(II), and Cd(II) were removed, respectively.
Humus is an important parameter to affect the environmental fate of arsenic (As) in tailing soil. According to the batch and column experiment, the effects of humus (HS) including humic acid (HA), fulvic acid (FA) on the As release and basic properties of soil were studied in the soil from a mining region. In addition, HA was modified by 3-mercaptopropyltrimethoxysilane (3-MPTS) with different sulfur content (S%) to improve the release capacity of As. The results indicated that HS could destroy the binding of As with Fe, Mn, Al and Ca without affecting the basic properties of tailings soil, thus achieving the co-release of As and associated metals. Besides, the As release capacity of FA (25.47 %) was slightly higher than that of HA (21.90 %). The ability of thiol-modified HAs to release As from tailings soil after being modified with different S% of 3-MPTS was significantly improved, of which 2 % had the best treatment. The thiol groups (-SH) reached 45.00 % of total S. With the increase of S%, the surface thoil content, aromatization degree and total reduction capacity (TRC) of HA increased. The study demonstrated that HS and thiol-modified HA could promote the migration of As and could advance the treatment of heavy metal contaminated tailing soil.
The various anthropological activities in this modern era of development has resulted into the mobilization and release of many heavy metals and their elements into the environment. Meanwhile, heavy metals from different sources are naturally nonbiodegradable and due to this fact, they accumulate into the environment and results in the contamination of food chain and leads to the risk to human health and as well as total environment. These heavy metals are causing serious threats as they are carcinogenic, mutagenic and also causes many diseases and disorders in children. So, remediation of these heavy metals accumulated in the environment is must and deserves serious attention. This chapters focusses on the various methods of remediation techniques that are employed in the removal of the heavy metals from the total environment.
The present book entitled “Current Research and Innovations in Life Sciences” gathers the recent and latest trends in innovative research achieved. The book is the most wide-ranging and convincing account available to analyze the multidisciplinary and multifaceted nature of innovations in the field of advances in Life Sciences. Each and every chapters contains comprehensive explanation on the projected topics with well explained appropriate tables and photo plates. This book composing of 13 highly selective chapters from 24 authors will present their many facets innovations in the context of historic, nature, development, managements and conservations in biology. The breadth of this work will allow the readers to gain the complete and panoramic view and can be used as reference source for various topics in biology.
In this work, the stability of arsenate adsorbed Mg(II)–Al(III)/Fe(III)–CO3/SO4 Layered Double Hydroxides (LDHs) under three abiotic anoxic reductive conditions that may be encountered in Tailings Management Facilities (TMFs) were evaluated. At pH 8 and 10 mM Fe(II) (aq), the formation of Fe(III)-oxy/hydroxides (FeOHs) occurred for all 5 LDHs but the Fe-based LDHs precipitated the greatest amounts. All LDHs released <0.3 mg/L total As(aq) and the reacted solid surface remained as As(V) except for MgFeSO4. For reactions at pH 8 and 0.5 mM Fe(II) (aq), precipitation of FeOHs occurred but preferential formation to magnetite (for MgFeSO4) and 2-line ferrihydrite (for MgFeCO3) transpired. The highest total As(aq) release followed the order: MgAlSO4 > MgAlFeCO3SO4 > MgAlCO3 > MgFeCO3/MgFeSO4. The solid surfaces remained as As(V) except for MgAlSO4, MgAlCO3, and MgAlFeCO3SO4 LDHs where 10–25% As(III) formed. Finally, at pH 10 and 0.5 mM Fe(II) (aq), the formation of FeOHs occurred to various degrees but a significant amount of CaCO3(s) precipitated. A 2-stage release and re-adsorption mechanism of total As(aq) occurred following the order: MgAlFeCO3SO4 > MgAlSO4 > MgFeCO3 > MgAlCO3 > MgFeSO4. A significant portion of the solid surfaces (30–90%) was found as As(III) for all reacted LDHs. This work provides a guideline for the environmental behavior of As(V) adsorbed LDHs where relevant underwater cover TMF abiotic reducing conditions may exist.
Humic acid (HA) is composed of a complex supramolecular association and is produced by humification of organic matters in soil environments. HA not only improves soil fertility, but also stimulates plant growth. Although numerous bioactivities of HA have been reported, the molecular evidences have not yet been elucidated. Here, we performed transcriptomic analysis to identify the HA-prompted molecular mechanisms in Arabidopsis. Gene ontology enrichment analysis revealed that HA up-regulates diverse genes involved in the response to stress, especially to heat. Heat stress causes dramatic induction in unique gene families such as Heat-Shock Protein (HSP) coding genes including HSP101, HSP81.1, HSP26.5, HSP23.6, and HSP17.6A. HSPs mainly function as molecular chaperones to protect against thermal denaturation of substrates and facilitate refolding of denatured substrates. Interestingly, wild-type plants grown in HA were heat-tolerant compared to those grown in the absence of HA, whereas Arabidopsis HSP101 null mutant (hot1) was insensitive to HA. We also validated that HA accelerates the transcriptional expression of HSPs. Overall, these results suggest that HSP101 is a molecular target of HA promoting heat-stress tolerance in Arabidopsis. Our transcriptome information contributes to understanding the acquired genetic and agronomic traits by HA conferring tolerance to environmental stresses in plants.
Climate change will affect water quality through a change in salinity, pH and organic matter (OM) content due to seawater intrusion, temperature change and subsurface biological processes. Therefore, a systematic evaluation of the impact of water quality variations is of particular importance to maintain the performance of a treatment process designed for drinking water. In this work, nanofiltration (NF) was investigated for the treatment of arsenic (As) contaminated water with the emphasis on water chemistry. Water salinity variations had no impact on the high rejection of As(V) with the studied NF membranes (NF270, NF90). The pH affects speciation and this significantly influenced the rejection of As(V) with NF270 (10–86%). The predominant mechanism was charge exclusion, while no effect was observed with NF90 (85–94%) where size exclusion plays the major role in rejection. The presence of humic acid (HA) in water has enhanced the rejection As(V) overall (10–20%) depending on water chemistry (pH, salinity) and membrane type. This study showed that NF technology was effective for As(V) rejection from water where seasonal changes in water quality can occur.
The ability of thiol-modified humic acids (HAs) to release arsenic in tailings soil after being modified with different sulfur-containing reagents were significantly improved. The structure and physicochemical properties of humic acid (HA) before and after thiol-modification were characterized. The 3-MPTS-HA treated with 3-mercaptopropyltrimethoxysilane (3-MPTS) effectively improved the mobility of arsenic, and its reducing ability was increased from 2 mmol g⁻¹ to 3.54 mmol g⁻¹. The S content of humic acids were also significantly increased after treatment with sulfur-containing reagents, in which the oxygen-containing functional group (e.g., C = O, C–O) on the surface of HA may be the active sites for binding with sulfur-containing reagents. It was found in the XPS spectrum that because the thiol group is easily oxidized, there are many S forms in thiol-modified HA. The –SH content in Na2S·9H2O-HA, l (+)-Cysteine-HA (Cys-HA), thioglycolic acid (TGA-HA) and 3-MPTS-HA was determined by fluorescence method to be 13.9, 78.45, 90.34, and 192.29 μmol g⁻¹, respectively. The study demonstrated that surface thiol modification can increase the abundance of thiol in HA and enhance reactivity, which will further promote the application of HA in the treatment of heavy metal contaminated tailing soil.
Organic ligand promoted dissolution of oxide minerals can be enhanced or inhibited in the presence of specifically adsorbed oxyanions. It has been proposed that an oxyanion inhibits or enhances dissolution depending on the type of surface complex formed and the strength of the bond. Mononuclear complexes (especially if they are bidentate) accelerate dissolution, while binuclear complexes inhibit dissolution. Recent spectroscopic evidence indicates that chromate and arsenate form different surface complexes depending on surface coverages. This study examined the influence of chromate and arsenate on the oxalate promoted dissolution of geothite. Based on a previous spectroscopic study, oxyanion surface coverages were varied to generate both mononuclear and binuclear surface complexes. Chromate and arsenate inhibited the oxalate promoted dissolution of geothite at all surface coverages investigated except at pH 6 (Γ(arsenate) = 1.70 x 10-6 and Γ(chromate) = 1.66 x 10-6 mol m-1). It is proposed that chromate and arsenate inhibit geothite dissolution by decreasing oxalate adsorption. This is accomplished because arsenate and chromate are more effective competitors for geothite surface sites than oxalate and upon adsorption increase the negative charge of the geothite surface. At pH 6 the adsorption of chromate and arsenate increases the negative charge of the geothite surface which in turn increases proton adsorption. Since proton adsorption is a necessary step for oxalate-promoted dissolution of geothite, and since proton activity at pH 6 is low, an increase in the negative charge of geothite upon adsorption of the oxyanions accelerates dissolution.
The solubility of a coal humic acid and the sorption of heavy metals (Cu-(II), Zn-(II), Co-(II), and Cd-(II)) in the absence and presence of the humic acid were determined as a function of pH and concentration of background electrolyte. The solubility of the humic acid at low electrolyte concentration increases in a a-step process with increase in pH. About 80% dissolves in the pH region 3-8.5, and the remainder in the region pH >8.5. The sorption of metals occurs at pH values significantly lower than those associated with the formation of insoluble metal hydroxides, with a maximum occurring in the pH region 5.5-7.5, and involves the solid state fraction of the humic acid. At the higher electrolyte concentration, the solubility of the humic acid is again a 2-step process but the increase in acid solution occurs over a relatively narrow pH range (5-6). At high pH, the presence of the humic acid significantly reduces the precipitation of the metals st both low and high salt concentration, probably due to the formation of soluble metal-humate species. There is evidence to suggest that the major functional group of the humic acid with which the metal cations interact is the carboxyl group.
The environmental fate of arsenic (As) is of utmost importance as the public and political debate continues with the USEPA's recent proposal to tighten the As drinking water standard from 50 to 10 μg L-1. In natural systems, the presence of dissolved organic C (DOC) may compete with As for adsorption sites on mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of arsenate [As (V)] and arsenite [As (III)] on goethite (α-FeOOH) was investigated in the presence of either a peat humic acid (Hap), a Suwannee River Fulvic Acid (FA) (International Humic Substances Society, St. Paul, MN), or citric acid (CA). Adsorption edges and kinetic experiments were used to examine the effects of equimolar concentrations of organic adsorbates on As adsorption. Adsorption edges were conducted across a pH range of 3 to 11, while the kinetic studies were conducted at pH 6.5 for As (V) and pH 5.0 for As (III). Both Hap and FA decreased As (V) adsorption, while CA had no effect. Humic acid reduced As (V) between pH 6 and 9 by ≈27%. Fulvic acid inhibited As (V) adsorption between pH 3 and 8 by a maximum of 17%. Arsenite adsorption was decreased by all three organic acids between pH 3 and 8 in the order of CA > FA ≈ Hap. The different pH regions in which Hap and FA decreased As (V) adsorption suggest that more than one functional group on these complex organic polymers may be responsible for binding to the α-FeOOH surface. Similarly, the relative surface affinity of the As(III or V) species and that of the competing organic ligand as a function of pH may play a major role in the outcome of As adsorption on α-FeOOH. The results of these experiments suggest that DOC substances are capable of increasing the bioavailability of As in soil and water systems in which the dominant solid phase is a crystalline iron oxide.
Organic ligand–promoted dissolution of oxide minerals can be enhanced or inhibited in the presence of specifically adsorbed oxyanions. It has been proposed that an oxyanion inhibits or enhances dissolution depending on the type of surface complex formed and the strength of the bond. Mononuclear complexes (especially if they are bidentate) accelerate dissolution, while binuclear complexes inhibit dissolution. Recent spectroscopic evidence indicates that chromate and arsenate form different surface complexes depending on surface coverages. This study examined the influence of chromate and arsenate on the oxalate promoted dissolution of goethite. Based on a previous spectroscopic study, oxyanion surface coverages were varied to generate both mononuclear and binuclear surface complexes. Chromate and arsenate inhibited the oxalate promoted dissolution of goethite at all surface coverages investigated except at pH 6 It is proposed that chromate and arsenate inhibit goethite dissolution by decreasing oxalate adsorption. This is accomplished because arsenate and chromate are more effective competitors for goethite surface sites than oxalate and upon adsorption increase the negative charge of the goethite surface. At pH 6 the adsorption of chromate and arsenate increases the negative charge of the goethite surface which in turn increases proton adsorption. Since proton adsorption is a necessary step for oxalate‐promoted dissolution of goethite, and since proton activity at pH 6 is low, an increase in the negative charge of goethite upon adsorption of the oxyanions accelerates dissolution.
Acid-base and complexation properties of humic acid (HA) isolated from a river sediment were studied by potentiometric titration, adopting the discrete site distribution model and the modified Gran functions for data fitting. Six classes of titratable groups were characterized, with pKa values between 2.4 and 10.2. Carboxylic groups accounted for 66% of the total of ionizable sites. The complexing properties were studied with regard to Cu2+, Pb2+, Cd2+ and Zn2+ ions by potentiometric titration using Cu ion selective electrode, or amalgam electrodes (Pb, Cd and Zn). The data treatment by the Scatchard method revealed two binding sites for copper and lead and one binding site for cadmium and zinc. The average stability constants were in the following order: log KHA-Cu > log KHA-Pb > log KHA-Cd @ log KHA-Zn, while the complexing capacity order, Cc, was: Pb > Cu > Cd @ Zn.
Arsenic (As) contamination in groundwater has received significant attention recently. Natural and anthropogenic sources contribute to the worldwide occurrence of As contamination. As speciation is an important factor related to its toxic and mobile behavior. The release of As from soils and sediments into groundwater is governed by several geophysicochemical processes, of which, As sorption behavior is of principle significance. This review paper summarizes existing information regarding the effects of natural organic matter (NOM) on the fate and mobility of As species in the environment. NOM may enhance the release of As from soils and sediments into the soil solution, thereby facilitating As leaching into the groundwater. The main influencing mechanisms include competition for available adsorption sites, formation of aqueous complexes, and/or changes in the redox potential of site surfaces and As redox speciation. NOM may also serve as binding agents, thereby reducing As mobility. However, comparably little research has been performed on this aspect. Since most investigations have been done on purified minerals under laboratory conditions, further research involving various geological materials under natural environmental conditions is required. Development of proper geochemical conceptual models may provide means of predicting the role of NOM in arsenic leaching and/or immobilization.
A number of experimental results are presented which show the variation of the pH values of several soils when samples of each are shaken with CaClâ solutions of different concentrations. These results are then interpreted on the basis of the ratio law-derived from the Gouy theory of the electrical double layer - and it is shown that the pH values and electrolyte concentrations show the expected relationship, provided the latter is not too large. The importance of the connection between pH and electrolyte concentration in the routine measurement of soil pH is emphasized, and it is pointed out that such measurements must be carried out using an electrolyte solution of known composition in order to obtain comparable results from different soils. It has been found that 0.01 M CaClâ is the most satisfactory for use in normal non-saline soils where the surface density of electrical charge on the colloidal material is high and independent of the solution composition: This electrolyte concentration is such that measurements made with the usual glass electrode/saturated calomel cell give accurate and reproducible values which are largely independent of the soil/solution ratio, and is yet sufficiently dilute to allow a satisfactory calculation of the lime potential characteristic of the soil sample.
The suitability of two procedures for the measurement of total surface area, based on 'the retention of ethylene glycol monoethyl ether (EGME), was investigated for a wide range of clay fractions and Australian soils. Experimental conditions for optimum precision and convenience of measurement were established. The procedures which utilized a higher vapour pressure of EGME achieved a higher retention of EGME by soils, reached the final condition of measurement more rapidly, and were less dependent on exchangeable cation status of the samples in confirmation of published work with pure smectite. The critical weakness of published procedures for soils is the assumption that the surface area occupied by an EGME molecule on a smectite reference sample can be applied to all soil surfaces. EGME retained per unit area by a range of soil and pure smectites, calculated from total surface area derived from crystal dimensions, and by a range of non-swelling minerals, related to measured BET-N2 areas, varied about fourfold between different mineral groups, and nearly twofold for different smectites. This variation could seriously over- or under-estimate estimates of total surface area, depending on the reference mineral chosen in relation to the mineral species being characterized. Alternatively, for soils free of clay minerals with internal surfaces, an empirical approach based on measured BET-N2 areas of representative soils may be feasible. A consideration of EGME retained in relation to BET-N2 areas may usefully complement X-ray diffraction procedures for characterizing randomly interstratified material in soil clay fractions.
Humic acid (HA) extracted from soil is investigated in terms of its cation exchange capacity (CEC), zero point of charge (zpc), oxygen containing functional group content, scanning electron microscope (SEM) images, and pH. The CEC of HA that was dried was approximately half the CEC of hydrated HA. Metal retention by HA was studied by conducting 24 h batch equilibrium tests with lead (Pb, as PbCl2) and cadmium (Cd, as CdCl2) and HA at pH 4 and 6, and with a mixture of HA, mackinawite and kaolinite. The reactivity of the HA towards Pb and Cd was reduced when it was combined with the mackinawite and kaolinite. The mackinawite raised the pH and dissolved some of the HA, until sufficient reactions between the metals and mixture lowered the pH enough for the dissolved HA to solidify and remove more metal from solution. HA bonding with the mackinawite and kaolinite reduced the HA sites available for metal uptake. The functional group content of the HA provided indications regarding the origin of the HA, the extent of humification and the presence of less decomposed fractions. The CEC of the HA could conservatively predict the amount of metal uptake. Low pH conditions are favorable for metal removal from solution by HA because the zpc of the HA was below pH 0.5 and because at higher pHs HA begins to dissolve. HA, especially in the hydrated phase, may represent an important material for metal removal from waters and wastewaters containing metals.
The influence of humate formation on the adsorption of various ions on kaolinite and amorphous silica was studied using the multitracer technique, i.e., the simultaneous application of a variety of radioactive tracers. The technique simultaneously provided the solid-aqueous distributions of 32 elements, namely, Be, Na, Sc, V, Cr, Mn, Fe, Co, Zn, Ga, As, Se, Rb, Sr, Y, Zr, Tc, Ru, Rh, Ag, Te, Ba, Ce, Pm, Eu, Gd, Tm, Yb, Lu, Hf, Re, and Pt, in the absence and presence of humic acid. Speciation calculations under experimental conditions were also conducted for 19 elements among them, using the previous results on the stability constants of their humate complexes. Comparison of the pH dependencies of each element and humic acid dissolved in the aqueous phase enabled the authors to evaluate the interaction between them. With the aid of the speciation calculation, the authors discussed the predominant species that would control the environmental behavior of each ion. Among the elements studied, it was suggested that humate formation greatly affects the behavior of rare earth elements, which would indicate that the environmental behavior of these ions is influenced by humic substances.
The adsorption of As(V) on alumina, hematite, kaolin and quartz has been measured as a function of pH (2 to 10), and As concentrations (10–4 to 10 –8 M; in the alumina and kaolin systems only). The effects of sulfate (0 to 80 mg L–1) and fulvic acid (0 to 25 mg L–1) were studied. The charge of the solid surface and the As speciation in solution (determined by pH) were the most important chemical parameters affecting the sorption behavior. At pH below PZC of the solid, there was a qualitative correlation between the adsorption and the anion exchange capacity of the solid. For hematite at low pH (below 5) there was a reduction of the adsorption possibly related to the formation of positively charged species. The presence of sulfate or fulvic acid reduced the adsorption.
Column experiments were conducted to evaluate the feasibility of using a rhamnolipid foam to remove heavy metals (Cd and Ni) from a sandy soil contaminated with Cd (1706 ppm) and Ni (2010 ppm). Best results were obtained from the foam generated by a 0.5% rhamnolipid solution with an initial pH value of 10.0 after flushing with 20-pore-volume of solution. These conditions removed 73.2% of the Cd and 68.1% of the Ni. Removal efficiencies by foam generated by a chemical surfactant, Triton X-100, were investigated as a comparison. It removed 65.5% of the Cd and 57.3% of the Ni under the same conditions. After a 20-pore-volume liquid solution flushing, 0.5% rhamnolipid (initial pH 10.0) without foam generation removed 61.7% of the Cd and 51.0% of the Ni, whereas 0.5% Triton X-100 (initial pH 10.0) removed 52.8% of the Cd and 45.2% of the Ni. Distilled water with adjusted pH only was also used to flush through the contaminated soil column as a control. It removed 17.8% of the Cd and 18.7% of the Ni. This study shows that rhamnolipid foam technology can be an effective means for the remediation of cadmium and nickel contaminated soil.
The influence of surface-bound fulvic acid on the sorption of Cu(II) to colloidal hematite particles was studied experimentally and the results were compared with model calculations based on the linear additivity assumption. In the first step, proton and Cu binding to colloidal hematite particles and to purified fulvic acid was studied by batch equilibration and ion-selective electrode titration experiments, respectively. The sorption data for these binary systems were modeled with a basic Stern surface complexation model for hematite and the NICA-Donnan model for fulvic acid. In the second step, pH-dependent sorption of Cu and fulvic acid in ternary systems containing Cu, hematite, and fulvic acid in NaNO3 electrolyte solutions was investigated in batch sorption experiments. Sorption of fulvic acid to the hematite decreased with increasing pH (pH 3–10) and decreasing ionic strength (0.01–0.1 M NaNO3), while the presence of 22 μM Cu had a small effect on fulvic acid sorption, only detectable at low ionic strength (0.01 M). Sorption of Cu to the solid phase separated by centrifugation was strongly affected by the presence of fulvic acid. Below pH 6, sorption of Cu to the solid phase increased by up to 40% compared with the pure hematite. Above pH 6, the presence of fulvic acid resulted in a decrease in Cu sorption due to increasing concentrations of dissolved metal-organic complexes. At low ionic strength (0.01 M), the effects of fulvic acid on Cu sorption to the solid phase were more pronounced than at higher ionic strength (0.1 M). Comparison of the experimental data with model calculations shows that Cu sorption in ternary hematite-fulvic acid systems is systematically underestimated by up to 30% using the linear additivity assumption. Therefore, specific interactions between organic matter and trace metal cations at mineral surfaces must be taken into account when applying surface complexation models to soils or sediments which contain oxides and natural organic matter.
A column experiment was conducted to investigate Zn, Cd, and Pb leaching from mine tailings as affected by the addition of organic amendments. Composted yard waste, composted cattle manure, and cattle manure aged for one month increased heavy metal leaching from mine tailings when compared to an unamended control. Aged cattle manure and composted cattle manure significantly increased Zn concentration in the leachate. The maximum Zn concentration in leachate from the manure-amended treatments was as high as 3.7 mg/L, whereas Zn concentrations from the control were less than 0.7 mg/L. All organic amendments increased Cd leachate concentrations. The presence of aged cattle manure greatly increased Pb concentrations in the leachate from less than 10 μg/L for the control treatment to higher than 60 μg/L. Lead concentration in leachate was positively correlated with inorganic carbon, total organic carbon, total carbon and bicarbonate. Although organic amendments increased Zn, Cd, and Pb leaching when compared with the control treatment, Zn concentrations were lower than the 5 mg/L secondary drinking water standard, and Pb concentrations were only minimally higher than the 15 μg/L drinking water standard. Cadmium concentrations from manure treatments exceeded the 5 μg/L drinking water standard but only during the first 15 days. Organic amendments may encourage establishment of vegetation in mining areas that may minimize heavy metal contamination through runoff and erosion. However, increased risk due to heavy metal leaching in the presence of organic amendments should be carefully considered.
An investigation of the sorption of As(III) and As(V) species by two humic acids (HA I and HA II) has shown that As uptake varies with pH, adsorbate concentration and ash content of the substrate. At fixed pH, the amount sorbed conformed to a Langmuir relationship, with calculated capacities in the region of maximum uptake (∼pH 5·5) being of the order of 70 (90) mmol kg−1 for As(III) and 90 (110) mmol kg−1 for As(V). The higher values (in parentheses) reflect the higher ash and Ca contents of HA II. Uptake decreased when the ash content was reduced by acid-washing or sample purification, or when F− or EDTA was added, indicating that Ca and polyvalent cations can be involved in As retention. The dominant solution species involved appear to be H3AsO3 and H2AsO4− and retention of these was subject to competition from other anions, in particular H2PO4−, and, to a lesser extent, CO32− and SO42−. The environmental significance of the results has been considered.
This study was undertaken to elucidate the interaction mechanism between NOM (natural organic matter) and iron oxide surfaces and to develop a predictive model for NOM adsorption and desorption. Results indicated that ligand exchange between carboxyl/hydroxyl functional groups of NOM and iron oxide surfaces was the dominant interaction mechanism, especially under acidic or slightly acidic pH conditions. This conclusion was supported by the measurements of heat of adsorption (microcalorimetry), FTIR and [sup 18]C NMR analysis, and competitive adsorption between NOM and some specifically adsorbed anions. A modified Langmuir model was proposed in which a surface excess-dependent affinity parameter was defined to account for a decreasing adsorption affinity with surface coverage due to the heterogeneity of NOM and adsorbent surfaces. With three adjustable parameters, the model is capable of describing a variety of adsorption isotherms. A hysteresis coefficient, h, was used to describe the hysteretic effect of adsorption reactions that, at h = 0, the reaction is completely reversible, whereas at h = 1, the reaction is completely irreversible. Fitted values of h for NOM desorption on iron oxide surfaces ranged from 0.72 to 0.92, suggesting that the adsorbed NOM was very difficult to be desorbed at a given pH and ionic composition. 54 refs., 8 figs., 3 tabs.
Soil flushing, an in situ process, can be used to remove metals from the soil by water or additives. The use of biosurfactants to enhance remediation of contaminants has recently received increasing interest, though research in this area has been limited. In this study, column experiments were conducted in three main phases. The first phase was to investigate the main parameters that influence the foam quality and stability. Foam generated by a rhamnolipid solution displayed high qualities from 90% to 99% and stabilities varied from 17 to 41 minutes. The second phase was carried out to study the pressure gradient build-up in the soil column with foam flowing through under different conditions (flow rate, foam quality, biosurfactant solution concentration), which varied from 0.3 kPa/cm to 6.6 kPa/cm. In the third phase, the biosurfactant (JBR425, mixed rhamnolipids) foam enhanced removal of heavy metals (Cd, Ni) from the contaminated soil was investigated. The soil was characterized as a sandy soil contaminated with Cd (1706 ppm) and Ni (2010 ppm). (Abstract shortened by UMI.)
Sediments dewatering is frequently necessary after dredging to remediate and treat contaminants. Methods include draining of the water in lagoons with or without coagulants and flocculants, or using presses or centrifuges. Treatment methods are similar to those used for soil and include pretreatment, physical separation, thermal processes, biological decontamination, stabilization/solidification and washing. However, compared to soil treatment, few remediation techniques have been commercially used for sediments. In this paper, a review of the methods that have been used and an evaluation of developed and developing technologies is made. Sequential extraction technique can be a useful tool for determining metal speciation before and after washing. Solidification/stabilization techniques are successful but significant monitoring is required, since the solidification process can be reversible. In addition, the presence of organics can reduce treatment efficiency. Vitrification is applicable for sediments but expensive. Only if a useful glass product can be sold will this process be economically viable. Thermal processes are only applicable for removal of volatile metals, such as mercury and costs are high. Biological processes are under development and have the potential to be low cost. Since few low cost metal treatment processes for sediments are available, there exists significant demand for further development. Pretreatment may be one of the methods that can reduce costs by reducing the volumes of sediments that need to be treated.
In order to investigate the influence of organic matter on arsenic retention, we used batch experiments at pH 7 to determine the adsorption of As(V) on three different solids: a crude, purified, Ca-exchanged kaolinite and two kaolinites coated with humic acids (HAs) having different nitrogen contents. We first examined the adsorption of each HA onto kaolinite, and then used the HA-kaolinite complexes to study As(V) adsorption. The results clearly show an influence of the HA coating on As adsorption. For example, with low initial As concentrations the solid/liquid partition coefficient (R(d)) for both HA complexes is greater than that for the crude kaolinite. We found that increasing the initial As concentrations decreased the R(d) values of the HA-coated kaolinites until finally they were the same as the crude kaolinite R(d) values. This suggests that adsorption occurs first on the HA sites and then, once the HA sites are saturated, on the remaining kaolinite sites. We also noted that the more reactive HA-kaolinite complex was the one with the highest N/C ratio. Comparing the amount of amine groups in the HA-kaolinite complexes with the total amount of adsorbed As indicates that the HA amine groups, due to their positive charge at pH 7, play a key role in the adsorption of As onto organic matter.
Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A for the exposed tailings and 3.33-3.35 A for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentate-binuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.
Humic substances (HS) are macromolecular products derived from a physical, chemical, and microbiological process called "humification." These substances play an important role in the mobility and bioavailability of nutrients and contaminants in the environment. Adsorption isotherms provide a macroscopic view of the retention phenomena. However, complementary techniques are needed in order to study the retention mechanism. The application of the classical models and some modern ones, based on humic substances chemistry, do not accurately describe these adsorption data. The aim of this paper is to model isotherms and combine adsorption data with spectroscopy and microscopy techniques to study the Cu(II) retention on a HS. The adsorption isotherms shape varies significantly with the solution pH from L-type (pH 2-6) to S-type (pH 8). FTIR shows that, when pH is 2 the retention of Cu(II), as [Cu(H(2)O)(6)](2+), is the preferred retention mechanism. The quantity of Cu(II) retained as [Cu(OH)(H(2)O)(6)](+) rises, as pH increases. At pH 4, Cu(II) begins to precipitate, which is the preferred mechanism at pH 8.02. The presence of HS has a great influence on the precipitation process of Cu(II), giving rise to amorphous precipitates. As it is shown by SEM-XRF, Cu(II) distributes heterogeneously on HS surface and accumulates on the humic phases. The presence of different anions (chloride and nitrate) slightly modifies the HS behavior as cation exchanger. When Cl(-) ions are present, part of the Cu(II) form [CuCl(4)](2-), which is stable in solution due to its negative charge; when the anion present is NO(3)(-) the formed complex, [CuNO(3)](+), is retained on the HS.
Soil contamination is notoriously difficult to treat because the contaminants are often tightly bound to the soil particles. Conventional remediation technologies are becoming less popular due to the high treatment costs. This paper gives a comprehensive overview and evaluation of an emerging promising alternative, surfactant foam technology. Different from other approaches, surfactant foam technology may be designed either to remove contaminants or/and simultaneously act as an augmentation for the existing technologies such as pump-and-treat systems and bioremediation processes to improve the contaminant removal efficiency and cost effectiveness. Encouraging results were achieved from laboratory and field demonstrations. However, as an innovative technology, there are many factors to be investigated with the future development. Special attention is paid to the selection of the most appropriate foaming surfactant and surfactant concentration, which are critical to the success of the implementation of the remediation process and have significant effects on the treatment costs. Moreover, development of predictive mathematical models in for future research is helpful to optimize the remediation process.
A greenhouse study was carried out with Brassica juncea to critically evaluate effects of bacterial inoculation on the uptake of heavy metals from Pb-Zn mine tailings by plants. Application of plant growth-promoting rhizobacteria, including nitrogen-fixing bacteria and phosphate and potassium solubilizers, might play an important role in the further development of phytoremediation techniques. The presence of these beneficial bacteria stimulated plant growth and protected the plant from metal toxicity. Inoculation with rhizobacteria had little influence on the metal concentrations in plant tissues, but produced a much larger above-ground biomass and altered metal bioavailability in the soil. As a consequence, higher efficiency of phytoextraction was obtained compared with control treatments.
Recently there has been increasing anxieties concerning arsenic related problems. Occurrence of arsenic contamination has been reported worldwide. In Canada, the main natural arsenic sources are weathering and erosion of arsenic-containing rocks and soil, while tailings from historic and recent gold mine operations and wood preservative facilities are the principal anthropogenic sources. Across Canada, the 24-h average concentration of arsenic in the atmosphere is generally less than 0.3 microg/m3. Arsenic concentrations in natural uncontaminated soil and sediments range from 4 to 150 mg/kg. In uncontaminated surface and ground waters, the arsenic concentration ranges from 0.001 to 0.005 mg/L. As a result of anthropogenic inputs, elevated arsenic levels, above ten to thousand times the Interim Maximum Acceptable Concentration (IMAC), have been reported in air, soil and sediment, surface water and groundwater, and biota in several regions. Most arsenic is of toxic inorganic forms. It is critical to recognize that such contamination imposes serious harmful effects on various aquatic and terrestrial organisms and human health ultimately. Serious incidences of acute and chronic arsenic poisonings have been revealed. Through examination of the available literature, screening and selecting existing data, this paper provides an analysis of the currently available information on recognized problem areas, and an overview of current knowledge of the principal hydrogeochemical processes of arsenic transportation and transformation. However, a more detailed understanding of local sources of arsenic and mechanisms of arsenic release is required. More extensive studies will be required for building practical guidance on avoiding and reducing arsenic contamination. Bioremediation and hyperaccumulation are emerging innovative technologies for the remediation of arsenic contaminated sites. Natural attenuation may be utilized as a potential in situ remedial option. Further investigations are needed to evaluate its applicability.
A critical examination of published data obtained primarily from recent nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization-mass spectrometry, and pyrolysis studies reveals an evolving new view of the molecular structure of soil humic substances. According to the new view, humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules intimately associated with a humic substance, such that they cannot be separated effectively by chemical or physical methods. Thus biomolecules strongly bound within humic fractions are by definition humic components, a conclusion that necessarily calls into question key biogeochemical pathways traditionally thought to be required for the formation of humic substances. Further research is needed to elucidate the intermolecular interactions that link humic components into supramolecular associations and to establish the pathways by which these associations emerge from the degradation of organic litter.
Arsenic (As) contamination presents a hazard in many countries. Natural attenuation (NA) of As-contaminated soils and groundwater may be a cost-effective in situ remedial option. It relies on the site intrinsic assimilative capacity and allows in-place cleanup. Sorption to solid phases is the principal mechanism immobilizing As in soils and removing it from groundwater. Hydroxides of iron, aluminum and manganese, clay and sulfide minerals, and natural organic matter are commonly associated with soils and aquifer sediments, and have been shown to be significant As adsorbents. The extent of sorption is influenced by As speciation and the site geochemical conditions such as pH, redox potential, and the co-occurring ions. Microbial activity may catalyze the transformation of As species, or mediate redox reactions thus influencing As mobility. Plants that are capable of hyperaccumulating As may translocate As from contaminated soils and groundwater to their tissues, providing the basis for phytoremediation. However, NA is subject to hydrological changes and may take substantial periods of time, thus requiring long-term monitoring. The current understanding of As NA processes remains limited. Sufficient site characterization is critical to the success of NA. Further research is required to develop conceptual and mathematical models to predict the fate and transport of As and to evaluate the site NA capacity. Engineering enhanced NA using environmentally benign products may be an effective alternative.
The fate of arsenic in the aquatic environment is influenced by dissolved natural organic matter (DOM). Using an equilibrium dialysis method, conditional distribution coefficients (Dom) for As(III) and As(V) binding onto two commercial humic acids were determined at environmentally relevant As/dissolved organic carbon (DOC) ratios and as a function of pH. At all pH values, As(V) was more strongly bound than As(III). Maximum binding was observed around pH 7, which is consistent with H+ competition for binding sites at low pH values and OH- competition for the arsenic center at high pH. For both oxidation states, Dom values increased with decreasing As/DOC ratios. Dom values were fitted as a function of the As/DOC ratio for As(III) and As(V). Compared to the aquatic humic acid, the terrestrial humic acid had a higher affinity for arsenic binding with 1.5-3 times higher Dom values under the same conditions. Al3+ in excess to arsenic successfully competed for strong binding sites at low As/DOC ratios. Under environmentally relevant conditions, about 10% of total As(V) may be bound to DOM, whereas >10% of As(III) is bound to DOM at very low As/DOC ratios only. Binding of arsenic to DOM should be considered in natural systems.
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