Figure - available from: Vadose Zone Journal
This content is subject to copyright. Terms and conditions apply.
Conceptual illustration of different types of porosity present in sand–biochar mixtures. Orange indicates sand particles that result in a relatively narrow pore size distribution, whereas the black area indicates biochar with a heterogeneous pore size distribution with both large and small pores.
Source publication
Core Ideas
Water retention and spectral induced polarization were measured for biochar in sand.
Water retention curves could be fitted by using a dual porosity model.
Residual water content was found to increase with the addition of biochar.
The polarization of sand–biochar mixtures was much larger than that for sand.
Spectral induced polarization...
Similar publications
Increasing wildfire frequency in the Mediterranean Basin could affect future plant-soil–water-dynamics. The capacity of soils to retain water is a key parameter affecting plant post-fire regeneration. Yet, few research has looked at how different soil properties related to water retention is affected by increasing wildfire frequency. This study aim...
Citations
... A handful of studies have used SIP to investigate the remedial performance of carbon-rich materials, such as biochar and AC (e.g., Gao et al., 2019;Kirmizakis et al., 2020;Siddiq et al., 2021). Gao et al. (2017) examined biochar within a sand matrix using SIP, showing frequency-dependent responses that are influenced by the degree of carbonization and graphitization. ...
Monitoring the remediation of soil and groundwater contaminated by organic compounds remains highly
challenging. Thermal treatments, such as smoldering combustion, have become established remediation techniques for destroying contaminants. Smoldering combustion can now be supported by colloidal activated carbon
(CAC), with CAC being able to both adsorb contaminants and supplement the fuel source for destroying them.
Despite this potential, effective performance monitoring of smoldering remediation remains limited. The
objective of this study is to investigate the potential of the spectral induced polarization (SIP) geoelectrical
technique to assess the performance of smoldering remediation of soils supplemented with CAC. SIP column
experiments were first conducted to assess the response of SIP (i.e., real and imaginary components of the
complex electrical conductivity) to varying concentrations of CAC in imitated field soils that contain, or do not
contain, organic matter (OM). Results demonstrate that increasing OM and CAC contents increase both the real
and imaginary conductivities, with the imaginary conductivity also showing frequency dependence. Smoldering
and SIP column experiments were then conducted to assess the effectiveness of SIP for detecting changes in soils
of varying OM and CAC contents that have been remediated by smoldering. Examination of the soils before and
after smoldering indicates that SIP can track the evolving real conductivity and imaginary conductivity (in
particular) between different soil compositions and different stages of the remedial process. High resolution
scanning electron microscopy imaging was performed on all samples to validate the SIP and smoldering experiments, confirming significant reductions in carbon after smoldering. Overall, this study suggests that SIP has
potential to track changes associated with the addition of remedial fluids like CAC in the subsurface, and the
destruction of contaminants adsorbed to CAC by smoldering combustion.
... The chargeability was related to the MP content (Gurin et al. 2013(Gurin et al. , 2015Revil et al. 2015a), their shape (Zhdanov 2008;Gurin et al. 2021), size (Gurin et al. 2013(Gurin et al. , 2015Revil et al. 2015aRevil et al. , 2015b, orientation relative to the electrical field (Gurin et al. 2021) and the matrix polarization (Gurin et al. 2015;Revil et al. 2015a). The relaxation time was related to the MP radius (Gurin et al. 2013(Gurin et al. , 2015, their mineral composition (Gurin et al. 2015), pore water electrical conductivity (Gurin et al. 2015;Revil et al. 2015aRevil et al. , 2015bPlacencia-Gomez & Slater 2016), electrical conductivity of the mixture (Gao et al. 2019;Martin et al. 2022) and the water chemical composition (Hubbard et al. 2014). In general, the trends shown in the aforementioned papers are consistent. ...
... We will discuss this paradoxical result in Section 6.1. With decrease of the porosity and respective increase of the model resistivity the relaxation time increases as τ ∼ ρ 0 , which corresponds to recent finding obtained with 'sand-MP' mixtures with various water saturation degree (Gao et al. 2019;Martin et al. 2022). ...
Induced polarization (IP) method is widely used in different applications including mining geology, hydrogeology, contaminant hydrology, geodynamics, and geothermal research. For this reason, petrophysical investigations of IP parameters present an increased interest. Last decades IP behavior of rocks and sediments containing metallic particles (MP) was extensively studied. Petrophysical investigations were performed mostly with synthetic granular models presented mixtures of sands and MP. In this paper, for the first time, we present IP data measured on a synthetic capillary model. The model made of Plexiglas contains a bundle of capillaries: some active (i.e. blocked by MP), others passive (open). In the experiments, we varied (i) the volumetric content of MP (ii) the water electrical resistivity, (iii) the model porosity, and (iv) the MP resistance. We found that the chargeability primarily depends on the ratio of the active to total surface of the pore cross-sections. Consequently, when the model contains only one active pore, and no passive pores, the chargeability is equal to 100 per cent. This is the case even if the volumetric content of MP is very small. This behavior of the capillary model is contrary to that of sand-MP mixture where the chargeability is approximately proportional to the volumetric MP content. We also found that the relaxation time of the capillary model depends on the bulk resistivity, the MP resistivity and the specific capacitance of the electrical double layer at the ‘MP—pore water’ interface. We explain the experimental data based on a new semi-empirical model. The model presents an extension of Pelton's (1978) model with explicit consideration of electrical and structural parameters of the capillaries.
... For simplification, the normalized chargeability ( , which is equal to the conductivity difference at high-limit and low-limit frequencies, is widely used to quantify the degree of polarization [34,37,38]. ...
In this paper, the adsorption process of copper ions on activated carbon (AC) was simulated in a column test. It was deduced that it is consistent with the pseudo-second-order model. Cation exchange was observed to be the major mechanism of Cu–AC interactions through scanning electron microscopy–energy dispersive X-ray spectroscopy (SEM–EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) measurements. Adsorption isotherms were fitted well using the Freundlich model. Adsorption thermodynamics at 298, 308, 318 K demonstrated that the adsorption process is spontaneous and endothermic. Spectral induced polarization (SIP) technique was used to monitor the adsorption process, and the double Cole–Cole model was used to analyze the SIP results. The normalized chargeability was proportional to the adsorbed copper content. Two measured relaxation times from the SIP testing were converted into the average pore sizes of 2, 0.8, 0.6, 100–110, 80–90, and 53–60 µm by the Schwartz equation, which are consistent with the measured pore sizes from both mercury intrusion porosimetry and scanning electron microscopy (SEM). The reduction in the pore sizes by SIP during the flow-through tests suggested that the adsorbed Cu2+ gradually migrated into small pores as with continued permeation of the influent. These results showcased the feasibility of using SIP technique in engineering practice involving the monitoring of copper contamination in land near a mine waste dump or in adjacent permeable reactive barriers.
... This method can be used to determine the polarization of electronically conductive particles that are disseminated in a matrix of other granular material and in contact with an electrolyte [63]. It has been proposed for the non-invasive characterization of biochar in soil [64][65][66]. ...
The knowledge of the structural and chemical properties of biochars is decisive for their application as technical products. For this reason, methods for the characterization of biochars that are generally applicable and allow quality control are highly desired. Several methods that have shown potential in other studies were used to investigate two activated carbons and seven biochars from different processes and feedstock. The chars were chosen to cover a wide range of chemical composition and structural properties as a hardness test for the analytical methods used in this study. Specific problems connected with the pretreatment of samples and drawbacks of some methods for some types of chars could be identified in an integrated consideration of the results from different methods. None of the spectroscopic methods was found to be suitable for the quality control of all types of chars. The most valuable results were obtained by chemical analysis that, however, required the complete determination of the main elements, including that of oxygen, and of inorganic components for adequate results. The combination of X-ray photoelectron spectroscopy (XPS) and FT-IR spectroscopy allows a rough characterization of surface functional groups, but cannot discriminate aliphatic and aromatic OH groups. FT-IR might be a suitable method for the quality control of biochars made at lower temperature. The results of Raman spectroscopy did not well correlate with the amount of sp ² hybridized carbon determined by XPS. A better correlation of XPS data was found with the electrical polarization determined by the method of spectral induced polarization that was used for the first time in conjunction with extensive analytical characterization.
... A growing amount of research suggests that SIP can be used to monitor the process of remediation of contaminants by porous materials at field scale. For instance, Gao et al. (2017Gao et al. ( , 2019 investigated the sensitivity of SIP to biochar in sand and the relation between the SIP response to the type and particle size of biochar, which the peak relaxation time and total chargeability in Debye model can interpret the SIP data, then electrolyte concentration and normalized total chargeability are positively correlated (Gao et al., 2017;Gao et al., 2019). Orozco et al. (2012) studied the relation between the SIP response and the concentrations of BTEX (benzene, toluene, ethylbenzene and xylene), and the result showed that the distribution of BTEX was unrelated to conductivity images and was negatively related to phase images. ...
... A growing amount of research suggests that SIP can be used to monitor the process of remediation of contaminants by porous materials at field scale. For instance, Gao et al. (2017Gao et al. ( , 2019 investigated the sensitivity of SIP to biochar in sand and the relation between the SIP response to the type and particle size of biochar, which the peak relaxation time and total chargeability in Debye model can interpret the SIP data, then electrolyte concentration and normalized total chargeability are positively correlated (Gao et al., 2017;Gao et al., 2019). Orozco et al. (2012) studied the relation between the SIP response and the concentrations of BTEX (benzene, toluene, ethylbenzene and xylene), and the result showed that the distribution of BTEX was unrelated to conductivity images and was negatively related to phase images. ...
Zeolite is utilized as an effective filling material in a permeable reactive barrier (PRB) at contaminated sites. Evaluation of the long-term performance of such barrier demands thorough understanding of the remediation mechanisms and real-time monitoring technique. In this study, the processes of zeolite remediation of three typical major contaminants from municipal solid waste sites (Chemical Oxygen Demand (COD), NH4⁺, and Pb²⁺, respectively) were simulated with column test, analyzed with microscopic methods (MIP, BET, SEM, XPS, FTIR, and XRD) and monitored with the spectral induced polarization (SIP) technique. Zeolite remediates COD simulant, KC8H5O4, through cation exchange of K⁺ and surface complexation of C8H5O4⁻. Patchy distribution of K⁺ with size range of 16–60 μm was both observed and calculated from the peak frequency of imaginary conductivity of SIP responses, which was attributed to the preferential complexation of C8H5O4⁻ at low velocity regions (dents) on zeolite surfaces. Zeolite remediates NH4⁺ mainly through ion exchange due to the higher affinity of NH4⁺ to zeolite surfaces than that of Na⁺. Zeolite remediates Pb²⁺ mainly through surface complexation, with clusters of complexed Pb (II) of wide size range (a few μm to 25 μm) residing on zeolite particle surfaces. The real conductivity of SIP responses for zeolite under contaminant flow-through is primarily sensitive to the ionic strength of influx fluid. A mean size of near 270 μm was calculated from SIP responses in all three cases, which was attributed to the pore throat of zeolite. Spectral induced polarization demonstrated its capability of monitoring three processes of zeolite remediating COD, NH4⁺, and Pb²⁺, respectively, and held promise of non-invasively monitoring of long-term performance of contaminant containing barriers.
... A few studies looked into the effect of carbon-based porous media on the spectral signature of soils (Gao et al., 2019;. Carbon-based porous materials (such as biochar and AC) are very conductive compared to the soil grains that are considered non-conductive other than EDL related surface processes (Gao et al., 2019). ...
... A few studies looked into the effect of carbon-based porous media on the spectral signature of soils (Gao et al., 2019;. Carbon-based porous materials (such as biochar and AC) are very conductive compared to the soil grains that are considered non-conductive other than EDL related surface processes (Gao et al., 2019). Gao et al. (2017) performed SIP measurements on soil mixed with four types of biochar at different mass fractions (biochar-amended soil). ...
Real-time, in-situ monitoring of adsorption processes in activated carbon (AC) filters may advance the effectiveness, reliability and economical value of such systems. In this study, the applicability of spectral induced polarization (SIP) as a real-time monitoring tool was examined. The adsorption of anionic and cationic organic dyes to commercial-AC filter was examined using a set of breakthrough experiments combined with continuous SIP monitoring. The imaginary part of the complex electrical conductivity decreased in the range of 0.25−2.5Hz for both dyes.
During the adsorption of the cationic dye, a new peak developed in the range of 7−40Hz, suggesting the dominance of surface processes that are not explained by the classic stern-layer polarization theory. The recorded imaginary conductivity values were used as a proxy for adsorbed dye concentration in the calibration process of a reactive transport model. The model confirmed that SIP can successfully be used for real-time monitoring of the dye progression through the filter. The applicability of SIP as an effective monitoring tool was also shown for cyclic operation (adsorption-desorption cycles).
... At present, there are some published works focusing on the complex conductivity (or spectral induced polarization (SIP)) measurements of soils in the frequency range below several tens of kHz. In these studies, the effect of the water saturation, which can be related to the VWC through the porosity, on the complex conductivity were investigated, and it was shown that the magnitude of complex conductivity, the in-phase conductivity, and even the quadrature conductivity follow power-law relations with the saturation [11][12][13][14][15]. Additionally, in some other works focusing on soil moisture measurements, the related electrical measurements were performed in wider frequency ranges of up to several MHz, and despite the presence of the effects of electrode polarization, the related results show good regular relations at different frequencies between the measured resistivity (or impedance, conductivity) and the water content [16][17][18]. ...
... The related equivalent circuit parameters can be found in Table 2, and the corresponding VWCs and dry densities are shown in Table 1. Overall, the characteristics for the change inσ subs with the increase in θ are similar to those forσ meas , i.e., the increase in θ primarily leads to the obvious and regular increase in |σ subs | and σ subs , and the conductive effect related to the substrate pore network filled with water plays a leading role; these results are relatively consistent with those in the previous studies [13][14][15]. * For the variable volumetric water contents (VWCs), the related dry densities (Table 1) are considered to be nearly equal. As shown in Figure 2, Q3 // R3, (R4 + Q2) // R2 and Q1 // R1 represent the resistive effects inside substrate grains, related to the substrate pore network and at the substrate-electrode interface, respectively. ...
... The related equivalent circuit parameters can be found in Table 2, and the corresponding VWCs and dry densities are shown in Table 1. Overall, the characteristics for the change in subŝ σ with the increase in θ are similar to those for meaŝ σ , i.e., the increase in θ primarily leads to the obvious and regular increase in subs σ and subs σ , and the conductive effect related to the substrate pore network filled with water plays a leading role; these results are relatively consistent with those in the previous studies [13][14][15]. ...
Electrical imaging studies of laboratory- and small-scale plant root zones are gaining increasing attention. However, for essential moisture–conductivity calibrations on numerous substrate columns with variability in dry density, the use of one conventional strategy is relatively laborious or complicated. Thus, in this work, a relatively convenient calibration method is presented, and the objective is to identify its feasibility and potential to assess the effects of factors (e.g., volumetric water content (VWC), and dry density) on conductivity and establish necessary moisture–conductivity curves for porous materials (e.g., soils and substrates). In the method, with a specially designed fixture, variable VWCs, dry densities and related complex conductivities of the samples can be easily acquired through static compaction. The results show that the in-phase conductivity (or magnitude of conductivity) increases with the increasing VWC or dry density, primarily owing to the increase in the dominant pore water connectivity. Moreover, the effect of dry density on conductivity is relatively smaller than that of VWC. Thus, for the substrates at dry densities with certain variability, good power law relations (R2 ≥ 0.99) between in-phase conductivity (or magnitude of conductivity) and VWC at different frequencies can be established. Overall, the proposed approach is practical, promising, and relatively time- and labor-saving.
... In the case of biochar as As remediation tool, the frequency-dependent induced polarization (spectral IP-SIP) could be a game changer (Atekwana and Slater 2009;Hördt et al. 2007), offering real-time information on surface processes that could be used to monitor sorption activity and significantly enhance remediation efficiency. Gao et al. (2019) monitored biochar properties when added to soil as an amendment where the SIP measured parameters showed a complex, but measurable, dependence on water saturation, suggesting SIP as a candidate tool for characterizing biochar in soils. Ntarlagiannis et al. (2016), and Kirmizakis et al. (2020) also observed the same dependence of the SIP parameters on biochar concentration in soil media, confirming the utility of the SIP method as a characterization tool. ...
Groundwater is considered as the primary source of drinking water in many countries around the world. For maintaining resource sustainability, clean and safe groundwater is a priority for water authorities worldwide. Unfortunately, groundwater resources are susceptible to various types of pollution, with arsenic (As) being a major pollutant in certain areas due to natural or anthropogenic activities. Due to its adverse health effects, As, a class-1 carcinogen, has been a topic of intense research. The technical difficulty and high cost incurred by conventional treatment systems for As removal have led many researchers to work on developing efficient, eco-friendly, and cost-effective technologies for the treatment of groundwater sources. Biochar has been widely used as an adsorbent for the decontamination of groundwater. High As removal rates have been achieved following metal (Fe, Zn, Mn) impregnation and magnetic modification to biochar. Despite numerous researches on biochar for As removal, very limited efforts have been made for upscaling to a convenient treatment system. Thus, this review highlights key findings of previous studies required for pragmatic applications. Following up with future trends, an overview is given on real-time monitoring techniques that can be combined with biochar for evaluating adsorption studies. Furthermore, research opportunities that exist in biochar adsorption studies have also been identified. This technical review is aimed for scientists, scholars and researchers as a supplementary guide for understanding As decontamination processes, highlighting the role of biochar as an adsorbent and conceptualizing the prospects of integration of real-time monitoring techniques.
