Soil Washing Solution Research Articles

A closed-loop process for spent washing solution from multi-metal contaminated soil: EDTA reclamation and recycling

The proper disposal of spent soil washing solution is a great challenge to ethylenediamine tetraacetate (EDTA)-base soil washing technologies, particularly when the solution contains multi-metals. In this paper, we proposed an environmentally friendly disposal of multi-metal spent washing solution, in which the multi-metals were concentrated as hazardous precipitates for further safe disposal, and EDTA was reclaimed and recycled to further wash contaminated soil together with the cleansed process water. The results showed that Cr3+ was poorly removed by sole heavy-metal-capturing agent (HMCA) chelation because of the high solubility of HMCA-Cr, which also yielded a low percentage of EDTA reclamation in the multi-metal spent washing solution. We established a closed-loop process for the disposal of multi-metal spent washing solution by combining coagulation-flocculation-sedimentation and HMCA chelation. The novel recycling process was able to remove 99.67% Cu, 99.62% Pb, 92.48% Cd, 88.19% Sb, 84.38% As, and 82.39% Cr as precipitates from the real spent washing solution, and up to 95.64% of EDTA was reclaimed in the cleansed process water. On the average, the overall efficiency of the reclaimed EDTA solution could reach 65% of the fresh EDTA solution in extracting various HMs from contaminated soil. The recycling method provides an efficient and promising alternative for spent soil washing solution with both EDTA and process water reusage in a closed-loop process.

Heavy metals removal from soil/sediments washing effluents via biocompatible aqueous two-phase systems

The generation of high amounts of soil/sediment washing solutions is one of the main concerns faced in ex situ treatment techniques, so in the present research, we have demonstrated the suitability of an organic salt like sodium potassium tartrate to efficiently promote phase segregation in a model soil washing solution containing biodegradable non-ionic-surfactants (Tween 80 and Tergitol 15S9) and heavy metals (copper, zinc, and cadmium), after a preliminary screening of the demixing effect of different inorganic and organic salts like ammonium nitrate, ammonium acetate and sodium potassium tartrate. The aqueous two-phase systems were characterized in depth at room temperature by defining the immiscibility region and correlating the experimental data with three empirical equations, and the results were discussed in the light of a thermodynamic function like the Gibbs free energy of hydration. Then, the applicability to extract the abovementioned metal ions was researched after TLs determination, observing high heavy metals extraction percentage (over 80 % in some cases). The extraction process was included in the soil washing process at real scale and it was simulated by means of the software SuperPro Designer, that makes up a valuable tool to ease the analysis of the technical viability of the proposed strategy.

Development of a potassium-based soil washing solution using response surface methodology for efficient removal of cesium contamination in soil

The overuse of chelating soil washing agents for removal of heavy metal can release soil nutrients and negatively affect organisms. Therefore, developing novel washing agents that can overcome these shortcomings is necessary. In this study, we tested potassium as a main solute of novel washing agent for cesium-contaminated field soil, owing to the physicochemical similarities between potassium and cesium. Response surface methodology was combined with a four-factor, three-level Box–Behnken design to determine the superlative washing conditions of the potassium-based solution for the removal of cesium from the soil. The parameters that were considered were the following: potassium concentration, liquid-to-soil ratio, washing time, and pH. Twenty-seven sets of experiments were conducted using the Box–Behnken design, and a second-order polynomial regression equation model was obtained from the results. Analysis of variance proved the significance and goodness of fit of the derived model. Three-dimensional response surface plots displayed the results of each parameter and their reciprocal interactions. The washing conditions that achieved the highest cesium removal efficiency (81.3%) in field soil contaminated at 1.47 mg/kg were determined to be the following: a potassium concentration of 1 M, a liquid-to-soil ratio of 20, washing time of 2 h, and a pH of 2.

Anchoring ZnO on spinel cobalt ferrite for highly synergic sono-photo-catalytic, surfactant-assisted PAH degradation from soil washing solutions

In this study, the photocatalytic activity of ZnO was effectively improved via its combination with spinel cobalt ferrite (SCF) nanoparticles. The catalytic performance of ZnO@SCF (ZSCF) was investigated in coupling with UV irradiation and ultrasound (US), as a heterogeneous sono-photocatalytic process, for the decontamination of phenanthrene (PHE) from contaminated soil. Soil washing tests were conducted in a batch environment, after extraction assisted by using Tween 80. Several characterization techniques such as XRD, FESEM-EDS, BET, TEM, UV–vis DRS, PL and VSM were utilized to determine the features of the as-prepared catalysts. ZSCF showed an excellent catalytic activity toward degradation of PHE in the presence of US and UV with a significant synergic effect. It was found that more than 93% of PHE (35 mg/L) and 87.5% of TOC could be eliminated by the integrated ZSCF/US/UV system under optimum operational conditions (pH: 8.0, ZSCF: 1.5 g/L, UV power: 6.0 W and US power: 70 W) within 90 min of reaction. After five times of use, ZSCF illustrated good reusability in the decontamination of PHE (87%) and TOC (79%). Quenching tests revealed the contribution of h+, HO• and e− species during PHE degradation over ZSCF/UV/US and an S-scheme photocatalytic mechanisms was proposed for the possible charge transfer routes under the ZSCF system. This study provides the important role of SCF in enhancing the ZnO photocatalytic activity due to its high performance, easy recovery and excellent durability, which it make an efficient and promising catalyst in environmental clean-up applications.

Integration of soil washing and cork permeable reactive barriers for the remediation of soil contaminated with polycyclic aromatic hydrocarbons

AbstractBACKGROUNDSoil washing is a well‐known technology for the remediation of soils polluted by organic contaminants, including polycyclic aromatic hydrocarbons (PAHs). This study aimed to go further by integrating soil washing and permeable reactive barriers (PRBs) made of cork granules to remove PAHs from the soil. While PAHs may be transferred from the soil to the washing solution in the soil washing step, the cork PRB may provide the removal of PAHs from the washing solution, ultimately leading to the reuse of this solution.RESULTSThe integrated approach was tested by means of packed bed column experiments in the absence and presence of cork PRBs. Two PAHs were under focus: fluorene (FLU) and phenanthrene (PHE). In soil with 0.5 mmol L−1 kgsoil−1 of FLU and PHE, the soil washing technique employing thermally treated cork granules and a solution of 70%/30% water/acetonitrile (v/v) flowing at 2.2 mL min−1 promoted the transfer of ~58% of PAHs from the soil to the washing solution, while the cork PRB retained ~98% of the PAHs from the washing solution. The acetonitrile content of the water/acetonitrile washing solutions contributed to the soil washing since it was responsible for PAH desorption and elution, however it was unfavorable for PAH sorption onto the cork as acetonitrile competed with PAHs for cork sorption sites.CONCLUSIONCork PRBs were able to retain PAHs from soil washing solutions and provide final solutions free of PAHs, demonstrating the viability of integrating solvent‐aided soil washing with cork PRBs. © 2022 Society of Chemical Industry (SCI).

Integrated soil washing and bioreactor systems for the treatment of hexachlorocyclohexane contaminated soil: A review on enhanced degradation mechanisms, and factors affecting soil washing and bioreactor performances

Investigations about the remediation of Hexachlorocyclohexane (HCH), a persistent organic pollutant of global concern, have been extensively reported to treat the HCH contaminated soil. The difficulty arising due to desorption and long ageing procedures of this hydrophobic organic compound in the soil, make it necessary to exploit techniques like soil washing or addition of surfactants, for enhancing the mass transfer rate of hydrophobic compounds. However, this technique gives rise to the generation of a large quantity of waste solution containing the pollutant and various other toxic substances. Moreover, it is challenging to deal with the complex soil washing solution, and thus a follow-up treatment of such washing solution is essentially required before its discharge. This follow-up treatment could be the bioreactor system to efficiently treat the pollutant in the wash solution, thereby reducing the amount of contaminated soil that has to be treated. Among many suggested remediation methods and treatment technologies, integrated soil washing and post-treatment with the bioreactor system could be an environmentally viable method for the remediation of HCH contaminated sites. This review focuses on the soil washing procedures applied so far for the HCH contaminated soil and various factors affecting the efficiency of separation of the target pollutant. Furthermore, the environmental and reactor design-related factors are also discussed for degradation of HCH in the reactor system. Finally, advantages and environmental feasibility of this proposed combined technology and the challenges that need to be encountered are envisaged.

PAHs biodegradation in soil washing effluent by native mixed bacteria embedded in polyvinyl alcohol-sodium alginate-nano alumina gel beads

In this study, the biodegradation of polycyclic aromatic hydrocarbons (PAHs) in soil washing solution containing Tween 80 was conducted using native mixed bacteria (Pseudomonas sp. Z1, Sphingobacterium sp. Z2, and Klebsiella sp. K) embedded in polyvinyl alcohol-sodium alginate-nano alumina (PVA-SA-ALNPs) gel beads. The optimal dosage of immobilized beads and embedded biomass for the biodegradation of phenanthrene (PHE), fluoranthene (FLU), and pyrene (PYR) were 10 % (v/v) and 20 % (v/v), respectively. SEM analysis showed that the porous structure of the immobilized beads was a cross-linked network with abundant pores that provided many potential adhesion sites for microorganisms. The beads with the immobilized mixed bacteria maintained a high activity during batch experiments and could even be reused for 3 cycles (90 d). Compared with the beads containing individual immobilized strain, the immobilized mixed bacteria showed a more efficient biodegradation of PHE (91.67 %), FLU (88.6 %), and PYR (88.5 %) in synthetic soil washing effluent within 30 d. The first-order kinetic model suitably described the degradation process of the three target PAHs. By adding Tween 80 to the synthetic eluent, the degradation of PHE, FLU, and PYR increased by 16.39 %, 22.25 %, and 21.29 %, respectively, indicating that Tween 80 promoted PAHs biodegradation, even though it was also rapidly degraded during the reaction cycle. These findings suggest that the developed mixed bacteria embedded in PVA-SA-ALNPs gel beads has great potential for PAHs remediation.

Triton X-100 improves the reactivity and selectivity of sulfidized nanoscale zerovalent iron toward tetrabromobisphenol A: Implications for groundwater and soil remediation

Sulfidized nanoscale zerovalent iron (SNZVI) with improved reactivity and selectivity has shown great potential for environmental remediation. However, it is unclear if SNZVI could be applied for the remediation of soil washing solution, and how a soil-washing surfactant affects the reactivity and selectivity of SNZVI. Here, we assess the impact of Triton X-100 (TX-100) on the reactivity and selectivity of a sulfidized commercial NZVI toward tetrabromobisphenol A (TBBPA). While sulfidation of NZVI improved its reactivity and electron efficiency toward TBBPA, TX-100 could further improve these promoting effects, which was 8–21 and 4–7 times higher than those without TX-100, respectively, depending on TX-100 concentration. Because TX-100 could induce the solubilization of TBBPA, sorb onto the SNZVI surface, and favor the subsequent sorption and degradation of TBBPA. SNZVI performance for successive treatments of TBBPA contaminated water was also greatly improved by TX-100. Moreover, washing the TBBPA-contaminated soil with TX-100 could efficiently extract the TBBPA, and almost all of the TBBPA in the soil washing solution could be efficiently degraded by SNZVI. These results suggest that TX-100 is a good additive to SNZVI for improving its performance, and SNZVI coupled with TX-100 can be a promising technology for the remediation of TBBPA-contaminated soil.

Response surface modeling with Box-Behnken design for strontium removal from soil by calcium-based solution.

Owing to its physicochemical similarity to strontium (Sr), calcium (Ca) was tested as a key component of a soil washing solution for Sr-contaminated soil collected near a nuclear power plant. A four-factor, three-level Box-Behnken experimental design combined with response surface modeling was employed to determine the optimal Sr washing condition for Ca-based solution. The Ca concentration (0.1-1M), liquid-to-soil ratio (5-20), washing time (0.5-2h), and pH (2.0-7.0) were tested as the independent variables. From the Box-Behnken design, 27 sets of experimental conditions were selected, and a second-order polynomial regression equation was derived. The significance of the independent parameters and interactions was tested by analysis of variance. Ca concentration was found to be the most influential factor. To determine whether the four variables were independent, three-dimensional (3D) response surface plots were established. The optimal washing condition was determined to be as follows: 1M Ca, L/S ratio of 20, 1h washing, and pH=2. Under this condition, the highest Sr removal efficiency (68.2%) was achieved on a soil contaminated with 90.1mg/kg of Sr. Results from five-step sequential extraction before and after washing showed that 84.0% and 82.9% of exchangeable and carbonate-bound Sr were released, respectively. In addition, more tightly bound Sr, such as Fe/Mn oxides-bound and organic matter-bound Sr, were also removed (86.2% and 64.5% removal, respectively).

Removal of PAHs at high concentrations in a soil washing solution containing TX-100 via simultaneous sorption and biodegradation processes by immobilized degrading bacteria in PVA-SA hydrogel beads

Soil washing process enhanced by surfactants is a promising technique in removing organic pollutants from soil. In this work, a simultaneous sorption and biodegradation technique was used to remove 16 PAHs from a soil washing solution (SWS) obtained by rinsing a heavily contaminated soil from a coking plant with Triton X-100 (TX-100). This was done by immobilizing a pyrene-degrading bacterial strain in polyvinyl alcohol-sodium alginate (PVA-SA) hydrogel beads. Removal performance of free bacteria, blank PVA-SA beads and beads with immobilized degrading bacteria at a low, medium and high initial concentration was evaluated. The recycling and removal performance of the used beads were also examined. Our findings showed that hydrogel beads with immobilized bacteria at a medium concentration can remove around 77% ∑16PAHs from SWS in 96 h. The beads can be recycled and reused to treat a new SWS; 32–55% ∑16PAHs was removed in 24 h. The bead provided protection for bacteria against the co-existing substances such as TX-100. The bacteria-immobilized beads are more efficient and sustainable than free bacteria and blank beads due to simultaneous sorption and biodegradation processes, thus providing a solid reference for possible industrial application of bacteria immobilization technique to deal with SWSs with complex composition.

Feasibility of soil washing agents to remove fluoride and risk assessment of fluoride-contaminated soils

The objectives of this study are to find the most suitable soil washing agent and the optimal concentration for fluoride removal and to further provide insights into fluoride-contaminated soil washing. The effects of the washing solution, the concentration, and the particle size of soil on the fluoride removal efficiency were investigated. Evaluation of the feasibility of ZrO2 to treat soil-washing wastewater and risk assessment of fluoride contaminated soil before and after soil washing were also conducted. The fluoride concentration in soil was measured following the standard method, and the fluoride concentration in solution was measured following 2-(parasulfophenylazo)-1,8-dihydroxy-3,6-naphthalene-disulfonate (SPADNS) spectrophotometric method. Sulfuric acid (H2SO4) showed the highest fluoride removal efficiency. The dominant fraction of F was the residual fraction before and after soil washing. ZrO2 injection showed 97.9% of fluoride removal efficiency in the post-treatment of soil-washing wastewater. The hazard quotient for non-carcinogenic risk was 1.12 × 10−2 for adults and 1.04 × 10−1 for children, respectively. The results indicated that 1 M of H2SO4 could meet Korean soil standard (400 mg/kg) as soil washing solution. These results indicated that the soil washing of fluoride-contaminated soil with H2SO4 could be a feasible technique for soil remediation.

Effect of Soil Washing Solutions on Simultaneous Removal of Heavy Metals and Arsenic from Contaminated Soil

In this study, we investigated the feasibility of using a solution of sulfuric acid and phosphoric acid as an extraction method for soil-washing to remove Cu, Pb, Zn, and As from contaminated soil. We treated various soil particles, including seven fraction sizes, using sulfuric acid. In addition, to improve Cu, Pb, Zn, and As removal efficiencies, washing agents were compared through batch experiments. The results showed that each agent behaved differently when reacting with heavy metals (Cu, Pb, and Zn) and As. Sulfuric acid was more effective in extracting heavy metals than in extracting As. However, phosphoric acid was not effective in extracting heavy metals. Compared with each inorganic acid, As removal from soil by washing agents increased in the order of sulfuric acid (35.81%) < phosphoric acid (62.96%). Therefore, an enhanced mixture solution using sulfuric acid and phosphoric acid to simultaneously remove heavy metals and As from contaminated soils was investigated. Sulfuric acid at 0.6 M was adopted to combine with 0.6 M phosphoric acid to obtain the mixture solution (1:1) that was used to determine the effect for the simultaneous removal of both heavy metals and As from the contaminated soil. The removal efficiencies of As, Cu, Pb, and Zn were 70.5%, 79.6%, 80.1%, and 71.2%, respectively. The combination of sulfuric acid with phosphoric acid increased the overall As and heavy metal extraction efficiencies from the contaminated soil samples. With the combined effect of dissolving oxides and ion exchange under combined washings, the removal efficiencies of heavy metals and As were higher than those of single washings.

Enhancement of tartaric acid modified washing solutions for lead decontamination of tropical soils

Abstract Tartaric acid is generally not an effective soil washing solution, hence this study focuses on enhancing its usage for soil-Pb decontamination. Three tropical soil types (sandy, clay and loamy) with different lead concentrations were subjected to single batch washing using 0.01, 0.1, 0.5 and 1 M tartaric acid with 5% and 10% KCl modification at 3% soil-pulp-density for 2, 6, 12 and 24 h washing time. The optimum washing conditions were 1 M tartaric acid at 24 h washing time, with Pb removal efficiency: sandy- 94.3%, clay-67.6% and loamy-36.8%. Modification of tartaric acid with 5% and 10% KCl brought about some degree of enhancement of Pb removal efficiency especially for clay and loamy soils. Removal efficiency for 5% KCl modification were: sandy-97.9%, clay-96.2% with 1 M tartaric acid at 24 h washing time, loamy-76.7% for 0.5 M tartaric acid. Similarly, 10% KCl modification were: sandy-96.7%, clay-97.2% for 1 M tartaric acid at 24 h, loamy-82.1% for 0.5 M tartaric acid. Removal efficiency was soil concentration dependent. Generally, removal efficiency increased with increasing tartaric acid concentrations and washing time. Tartaric acid washing is promising and recommended in events of moderate contamination and 10% KCl modification in event of high level contamination. Further study is needed on enhancing very low concentrations of tartaric acid for large scale applications.

Phenanthrene degradation using Fe(III)-EDDS photoactivation under simulated solar light: A model for soil washing effluent treatment

In this work, for the first time, the nonionic surfactant polyoxyethylene-(20)-sorbitan monooleate (Tween 80, C64H124O26) aided soil washing effluent was treated by enhanced activation of persulfate (PS) using Fe(III)-EDDS (EDDS: ethylenediamine-N, N-disuccinic acid) complexes under simulated solar light irradiation. The performance of this system was followed via the production and reactivity of radical species (SO4-, HO, Cl2-) and degradation of phenanthrene (PHE) used as a model pollutant in soils. Different physico-chemical parameters such as the concentration of reactive species and pH were investigated through the PHE degradation efficiency. The second-order rate constants of the reactions for generated radicals with PHE and Tween 80 in solution were identified through competitive reaction experiments under steady-state conditions and application of nanosecond laser flash photolysis (LFP) as well. A kinetic approach was applied to assess the selectivity and reactivity of photo-generated radicals in aqueous medium in order to explain the observed degradation trends. This work proposes an innovative technology of management of soil washing solutions using Fe(III)-EDDS complexes and solar light for the activation of persulfate.

Environmental Applications of Boron‐Doped Diamond Electrodes: 2. Soil Remediation and Sensing Applications

AbstractThe chemical stability and electrocatalytic properties of boron‐doped diamond (BDD) electrodes give rise to various applications. While wastewater treatment is the most widely studied field, the use of BDD for soil remediation and environmental sensing is currently investigated more and more. With regards to soil remediation, promising results have been reported for the treatment of soil washing solutions. Anodic oxidation using BDD at high current density allows high mineralization rates of biorefractory soil pollutants and extracting agents to be reached. At low current density, selective degradation of target pollutants has been achieved, thus allowing the reuse of extracting agents for further soil washing steps. BDD‐based electrochemical sensors have been studied for chemical oxygen demand determination, pesticide/pharmaceutical detection as well as other applications such as pH, O2 and analysis of various organic and inorganic compounds. Low detection limits, wide linear ranges and low standard deviations have been achieved. The main reasons behind the superiority of BDD sensors are the chemical stability, wide applicability and resistance of BDD towards biofouling. The beauty of BDD sensing is that it can work for a variety of organic and inorganic compounds under many physicochemical parameters.

Dechelation of Cd-EDTA complex and recovery of EDTA from simulated soil-washing solution with sodium sulfide

Washing water containing poorly degradable heavy metal-EDTA complexes is produced by ethylenediaminetetraacetic acid (EDTA) washing of heavy metal-contaminated soil. A series of batch experiments were performed to explore the dechelation of heavy metal-EDTA complexes and the recovery of EDTA from simulated soil-washing solution using sulfide precipitation with Na2S. The results showed that the effect of Na2S dosage on the dechelation of Cd-EDTA solution was greater than that of other factors (reaction temperature, time, and pH) and excess EDTA suppressed cadmium removal. Additionally, the Cd removal efficiency reached 99.99 ± 0.001%, and the residual amount of Cd-EDTA was below the detection limit of ion chromatography (IC) measurements under the following optimal conditions: an initial Cd-EDTA solution pH of 6, a sodium sulfide-to-Cd-EDTA ratio of 2:1, a reaction temperature of 25 °C, and a contact time of 20 min. Furthermore, the results of analysis using inductively coupled plasma optical emission spectroscopy (ICP-OES), Fourier transform infrared (FT-IR) spectroscopy, and ion chromatography (IC) confirmed that the dechelation process could be completed in less than 20 min and that EDTA was completely recovered as trisodium EDTA (HNa3EDTA). The mechanism for the dechelation of Cd-EDTA and recovery of EDTA using sulfide precipitation with Na2S was also proposed. The recovered EDTA with acidification had the same ability to extract heavy metals from soil with fresh EDTA. This study may facilitate the recycling of soil-washing wastewater and reduce the cost of extracting heavy metals from soil using EDTA.

Degradation of α-HCH in Soil Washing Solutions with nZVI and CaO2

Nano zerovalent iron (nZVI) and CaO2 were used to construct a heterogeneous Fenton-like system to degrade α-hexachlorocyclohexane (α-HCH) in soil solution, and the degradation efficiency and mechanism were investigated. The results showed that nZVI/CaO2 can degrade α-HCH in an extensive pH range. When the dosage of nZVI and CaO2 was 1 g·L-1 and pH was 5, the degradation rate of α-HCH reached 93.23%. The degradation process of nZVI, CaO2, and nZVI/CaO2 treatments accorded with the first-order reaction kinetics model. The reaction rate constant of nZVI/CaO2 was greater than the sum of individual treatments, showing that nZVI/CaO2 has a synergistic effect on the degradation of α-HCH. Through quenching free radical experiments, the contribution rate of superoxide radicals was shown to be greater than that of hydroxyl radicals. Intermediates, including trichlorobenzene and chlorobenzene, were detected. The content of trichlorobenzene showed a sharp increase initially, and then decreased quickly. The chlorobenzene content was low and showed little change. The α-HCH in the soil washing solution was first reduced to trichlorobenzene, which was further reduced to chlorobenzene or mineralized into CO2 and water directly.

Anodic oxidation of surfactants and organic compounds entrapped in micelles – Selective degradation mechanisms and soil washing solution reuse

Formation of micelles at high surfactant concentration strongly modifies organic pollutant oxidation mechanisms and kinetics during anodic oxidation (AO) using boron doped diamond (BDD) anode. Results presented and discussed in this study emphasized the following mechanisms: (i) micelles act as a protective environment and reduce the availability of target molecules towards BDD(•OH); (ii) the use of low current density strongly reduces micelle degradation kinetics due to both steric hindrance phenomenon for oxidation of micelles at the BDD surface and decrease of mediated oxidation in the bulk; (iii) compounds solubilized in surfactant-containing solutions can be either oxidized after degradation of the protective environment formed by micelles or if they are present as free extra-micellar compounds. Therefore, selective degradation of organic compounds entrapped in micelles can be achieved by using low current density and high surfactant concentration. In fact, these operating conditions strongly hinder micelle oxidation, while free (extra-micellar) compounds can still be oxidized. Then, the remaining entrapped compounds can also be continuously released in the aqueous phase, according to the micellar/aqueous phase partitioning coefficient (Km). These results have been applied for the treatment of a real polycyclic aromatic hydrocarbon-containing soil washing (SW) solution. After 23 h of treatment at 2.1 mA cm−2, 83% of phenanthrene, 90% of anthracene, 77% of pyrene and 75% of fluoranthene were degraded and the treated SW solution was reused for an additional SW step with only 5% lower extraction capacity than a fresh TW80 solution. A comparative study highlighted the superiority of this treatment strategy, compared to the use of activated carbon for selective adsorption of polycyclic aromatic hydrocarbons and SW solution reuse.

An evaluation of different soil washing solutions for remediating arsenic-contaminated soils

Soil washing is a promising way to remediate arsenic-contaminated soils. Most research has mostly focused on seeking efficient extractants for removing arsenic, but not concerned with any changes in soil properties when using this technique. In this study, the removal of arsenic from a heavily contaminated soil employing different washing solutions including H3PO4, NaOH and dithionite in EDTA was conducted. Subsequently, the changes in soil physicochemical properties and phytotoxicity of each washing technique were evaluated. After washing with 2 M H3PO4, 2 M NaOH or 0.1 M dithionite in 0.1 M EDTA, the soil samples’ arsenic content met the clean-up levels stipulated in China’s environmental regulations. H3PO4 washing decreased soil pH, Ca, Mg, Al, Fe, and Mn concentrations but increased TN and TP contents. NaOH washing increased soil pH but decreased soil TOC, TN and TP contents. Dithionite in EDTA washing reduced soil TOC, Ca, Mg, Al, Fe, Mn and TP contents. A drastic color change was observed when the soil sample was washed with H3PO4 or 0.1 M dithionite in 0.1 M EDTA. After adjusting the soil pH to neutral, wheat planted in the soil sample washed by NaOH evidenced the best growth of all three treated soil samples. These results will help with selecting the best washing solution when remediating arsenic-contaminated soils in future engineering applications.

Advanced remediation of uranium-contaminated soil

The existing decontamination method using electrokinetic equipment after acidic washing for uranium-contaminated soil requires a long decontamination time and a significant amount of electric power. However, after soil washing, with a sulfuric acid solution and an oxidant at 65 °C, the removal of the muddy solution using a 100 mesh sieve can decrease the radioactivity of the remaining coarse soil to the clearance level. Therefore, only a small amount of fine soil collected from the muddy solution requires the electrokinetic process for its decontamination. Furthermore, it is found that the selective removal of uranium from the sulfuric washing solution is not obtained using an anion exchanger but rather using a cation exchanger, unexpectedly. More than 90% of the uranium in the soil washing solutions is adsorbed on the S-950 resin, and 87% of the uranium adsorbed on S-950 is desorbed by washing with a 0.5 M Na2CO3 solution at 60 °C.