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Fourier-transform infrared spectroscopy of crop residues and biochars pyrolyzed at different temperatures
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The mechanism of Cr(VI) immobilization in soils by organic substances are not well understood. In the present study, two crop residues (maize stalk and peanut shell) and their biochars obtained at various pyrolysis temperatures were prepared to investigate their influences on the immobilization of Cr(VI) in two contaminated soils via an incubation...
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Citations
... The kind of organic substances found in soils can also influence the immobilization of Cr(VI). Li et al. (2019), for example, observed that the ability of crop residues to reduce Cr(VI) to Cr(III) was higher than that of their respective biochars. In this case, the carbonization process accelerates the decomposition of functional groups of oxygen-containing organic substances. ...
The removal of Cr(VI) from the solution by components of Oxisol (O) and peat (P) was evaluated as part of a nature-based solution. O and P were evaluated separately, mixed (OP), and by adding an Fe(III) salt to the peat sample (PFe) under natural soil pH (5–6) and acidity (pH < 2) conditions. Batch tests were conducted to evaluate the effect of contact time (10 min to 48 h) and initial Cr(VI) concentration (10 to 300 mg L−1) on Cr(VI) removal. All samples were able to remove Cr(VI) from the solution. However, this mechanism varied according to the pH condition. Under the natural soil pH, the humic substances (HS) of Oxisol and peat (such as carbonyl, hydroxyl, and aromatic groups) were the main Cr(VI) reducing agents. This chemical reaction was slow, as it took about 48 h to reach maximum removal. In the PFe sample and those subjected to the acidic condition, Cr(VI) ions were reduced rapidly (about 1 h) by Fe(II) ions, formed from Fe(III) reduction by HS. All Cr(III) ions formed under natural soil pH were removed from the solution by precipitation and/or complexation/adsorption with carboxylic groups and some soil minerals. Under acidic conditions, Cr(III) ions remained in the solution due to the low pH (<2). This study revealed that under natural soil pH, Oxisol and peat components are able to reduce Cr(VI) as well as immobilize the Cr(III), favoring a nature-based solution.
... Plant and fungi residues (Jobby et al., 2018), peat (Antoniadis et al., 2018), manure (Wu et al., 2017) and other organic residues (Rendina et al., 2011;Song et al., 2019) have shown promising results. Biochar can also be a good alternative, but attention should be paid to the carbonization process to preserve the above-mentioned functional groups (Li et al., 2019). In addition, sewage sludge can be used as soil amendment to increase the biomass of the plants, which implies an improvement in their phytoextraction capacity for phytomining purposes (Rosenkranz et al., 2017;Rue et al., 2019). ...
This work investigates the mechanisms determining Cr speciation and availability in two different soils polluted with two chromium sources (an industrial sludge, highly polluted with Cr, and Cr(VI) solution) and the influence of these parameters on the recovery of the soil functions related with biological quality and plant growth. The experiment was carried out in greenhouse conditions using 36 pots of 17 kg for the growth of Silene vulgaris for 21 months. Logistic Regression Model using Lasso estimator shows that soil organic matter (SOM) and pH control Cr availability in studied soils. In soils treated with the sludge, X ray Absorption spectroscopy showed that Cr was present as Cr(III), biological quality indicators increased and plants were able to grow. However, in soils polluted with Cr(VI), Cr availability was significantly different in the two soils. In the alkaline and poor in organic matter soil, 12% of Cr(VI) remained in the soil leading to the decrease of soil quality indicators and the total inhibition of plant growth. In the neutral soil, Cr(VI) was totally reduced to Cr(III) by soil organic matter (SOM), quality indicators were not affected and plants grown properly. Infrared Spectroscopy showed that different functional groups reacted with Cr in the two soils. This study highlights the importance to understand the mechanisms underlaying Cr redox and adsorption reactions in Cr polluted soils as they determine the potential recovery of the functions related with biological quality indicators and plant growth. The methodology proposed allows this study in complex soil samples at realistic concentrations and may be useful for risk assessment and for the planning of managing strategies in Cr polluted soils.
... Plant and fungi residues (Jobby et al., 2018), peat (Antoniadis et al., 2018), manure (Wu et al., 2017) and other organic residues (Rendina et al., 2011;Song et al., 2019) have shown promising results. Biochar can also be a good alternative, but attention should be paid to the carbonization process to preserve the above-mentioned functional groups (Li et al., 2019). In addition, sewage sludge can be used as soil amendment to increase the biomass of the plants, which implies an improvement in their phytoextraction capacity for phytomining purposes (Rosenkranz et al., 2017;Rue et al., 2019). ...
This work investigates the mechanisms determining Cr speciation and availability in two different soils polluted with two chromium sources (an industrial sludge, highly polluted with Cr, and Cr(VI) solution) and the influence of these parameters on the recovery of the soil functions related with biological quality and plant growth. The experiment was carried out in greenhouse conditions using 36 pots of 17 kg for the growth of Silene vulgaris for 21 months. Logistic Regression Model using Lasso estimator shows that soil organic matter (SOM) and pH control Cr availability in studied soils. In soils treated with the sludge, X ray Absorption spectroscopy showed that Cr was present as Cr(III), biological quality indicators increased and plants were able to grow. However, in soils polluted with Cr(VI), Cr availability was significantly different in the two soils. In the alkaline and poor in organic matter soil, 12% of Cr(VI) remained in the soil leading to the decrease of soil quality indicators and the total inhibition of plant growth. In the neutral soil, Cr(VI) was totally reduced to Cr(III) by soil organic matter (SOM), quality indicators were not affected and plants grown properly. Infrared Spectroscopy showed that different functional groups reacted with Cr in the two soils. This study highlights the importance to understand the mechanisms underlaying Cr redox and adsorption reactions in Cr polluted soils as they determine the potential recovery of the functions related with biological quality indicators and plant growth. The methodology proposed allows this study in complex soil samples at realistic concentrations and may be useful for risk assessment and for the planning of managing strategies in Cr polluted soils.
... us, green, environmentally friendly reducing agents must be urgently developed as substitutes for ferric salts and sulfides. e use of biochar as a reducing agent to remove Cr(VI) has been extensively investigated [8][9][10][11][12][13][14][15]. Dong et al. [8] successfully applied the biochar from sugar beet tailings to reduce Cr(VI) in aqueous solutions and obtained favorable results. ...
... Xia et al. [13] found that biochar is a promising material for remediated Cr(VI)-contaminated soils and wastewater, displaying factors that affect the removal efficiency of Cr(VI), including pH, temperature, initial concentration, reaction time, biochar characteristics, and coexisting contaminants. Li et al. [14] compared the biochars from maize stalk and peanut shell for reduced Cr(VI) in soils. eir results show that the maximum Cr(VI) reduction capacities of maize stalk and peanut shell were 238 and 231 mg/kg, respectively. ...
Background. Soil contamination by hexavalent chromium is becoming a main environmental concern in China. This study developed a sewage sludge biochar modified by FeSO4 (CHBC) as a new reductant for Cr(VI)-contaminated soil. The effectiveness of CHBC-stabilized Cr(VI)-contaminated soil was investigated. Methods. Typical industrial Cr(VI)-contaminated soil in China was chosen as the medium. The total and Cr(VI) contents of the contaminated soil were 1014.6 and 973.5 mg/kg, respectively. The effectiveness of the Cr(VI)-contaminated soil stabilized by CHBC was investigated by the leaching test (US EPA method 1312), the simplified bioaccessibility extraction test (US EPA 2007 protocol and British Geological Survey), alkaline digestion (US EPA method 3060A), sequential extraction (BCR sequential extraction procedure), X-ray diffraction, and the risk assessment code test. Results. Results show that CHBC substantially reduced the leachability and Cr(VI) content of the contaminated soil. The leachability and content of Cr(VI) were lower than the thresholds of the Environmental Quality Standards of Soil in China for civil reuse and the China Environmental Quality Standards of surface water for civil use when the soil was stabilized with 10% dosage of CHBC. Conclusion. CHBC is highly efficient in stabilizing Cr(VI) and can effectively reduce the leachability and bioavailability of Cr in contaminated soil and thus feasible for stabilizing Cr(VI)-contaminated soil and shows potential for application in the field.
Contamination of soil by toxic chromium (Cr) is a rising health issue due to over-exploitation and industrial production. Toxicity can be decreased by bioremediation because some microorganisms are able to convert highly toxic hexavalent chromium Cr(VI) into less toxic trivalent chromium Cr(III) by secreting chromate reductase. Moreover, microorganisms are able to remove Cr by adsorption on microbial cell walls. Plants can also be used for phytoremediation by uptaking Cr from soil into plant organs. Here, we review the speciation of Cr in soil, remediation methods to remove Cr, bioremediation challenges, and remaining ecological impacts after bioremediation. We present the mechanisms of microbial remediation, phytoremediation and plant–microbial combined remediation and applications.
