Contaminated Soil Column Research Articles

A facile “one-pot” synthesized CaAl MnO4 LDH with a high loading capacity of oxidants for the sustained oxidation of oxytetracycline in soil

This study aims to address previous issues such as low payload of sustained release materials and excessive consumption of oxidants by developing novel sustained-release oxidation agents. Through a one-pot synthesis method, MnO4- intercalated Ca-Al-layered double hydroxide (CaAl MnO4 LDH) was synthesized with an oxidant payload of 4.82 mmol/g, constituting 53.2 % of the total mass. MnO4- exists in the sustained-release material in two forms: 57 % in free state and 43 % intercalated. The free MnO4- rapidly degrades oxytetracycline (OTC), while the intercalated MnO4- is gradually released from the LDH interlayers through ion exchange and interface dissolution, continuously degrading OTC desorbed from the soil. Additionally, CaAl LDH readily releases Ca2+; the small molecular acids and CO2 generated after OTC degradation will re-fix Ca2+ to form CaCO3, achieving carbon sequestration and enhancing the utilization efficiency of Ca2+. In simulated OTC contaminated soil columns (50 mg/kg) treated with 0.5 wt% MnO4 LDH at a water flow rate of 0.04 ml/min, it was confirmed that the oxidant utilization efficiency of MnO4 LDH was 3.5 times higher than that of the KMnO4 system, removing 99.8 % of OTC within 40 days. This study provides new insights for the design of sustained-release materials and theoretical support for the remediation of organic pollutants.

Impacts of Nanobubbles in Pore Water on Heavy Metal Pollutant Release from Contaminated Soil Columns.

This study investigated the release of heavy metals from polluted soil under the pore water flow containing nanobubbles (NBs) to simulate natural ebullition. Three types of NBs (CH4, H2, and CO2) were generated in water and characterized, including bubble size, zeta potential, liquid density, and tension. The flow rate used in column tests was optimized to achieve proper soil fluidization and metal desorption or release. The leachate chemistries were monitored to assess the effect of NBs on conductivity, pH, oxidation-reduction potential (ORP), and dissolved oxygen (DO). The results showed that NBs in the pore water flow were significantly more effective in releasing Pb compared to DI water, with CO2 NB water being the most effective and H2 NB water being the least effective. CO2 NB water was also used to rinse column soil contaminated with four different metals (Pb, Cu, Zn, and Cr), which exhibited different leaching kinetics. Moreover, a convective-dispersion-deposition equation (CDDE) model accurately simulated the leaching kinetics and explained the effects of NBs on the key parameters, such as the deposition rate coefficient (Kd), that affect the released metal transport. The findings could provide new insights into soil pollutant release under ebullition and soil remediation using water wash containing NBs.

Foam flushing with soil vapor extraction for enhanced treatment of diesel contaminated soils in a one-dimensional column

A limitation of soil vapor extraction (SVE) remediation for total petroleum hydrocarbons (TPHs) in the unsaturated zone is the inability to remove the less volatile petroleum mixture compounds in diesel fuel. SVE combined with foam flushing may have the potential to enhance dissolution or mobilization of soil sorbed diesel and allow mobilized diesel to move to the SVE extraction well. A nonionic surfactant polyoxyethylene (20) sorbitan monooleate (TW80) was selected for generating foam, and a procedure to incorporate the oxidant sodium persulfate (SPS) in generating TW80/SPS foam to deliver chemical oxidation, was also studied. Both TW80 and TW80/SPS foams exhibited 96–98% quality under 8–32 mM of TW80 and 10–50 mM of SPS. The addition of SPS in TW80 solution resulted in elevated ionic content and degradation of TW80, which may reduce the foam stability and have minor effects on foam quality. Through analysis of interrelationships among column flushing experimental parameters, it was shown that the foam quality was reduced to 42–47% when foam flushed through a diesel contaminated soil column. Moreover, the results of column flushing tests operated for 12 h indicated that the effectiveness of removal of diesel by different foams followed the order of TW80 foam (53%) > TW80/SPS foam (37%) >N2 gas flow alone (3%). It was shown that foam flushing could be an alternative approach, rather than using N2 gas flow alone (SVE), in enhancing SVE for reducing diesel contamination in the unsaturated zone.

Sulfidated zero valent iron as a persulfate activator for oxidizing organophosphorus pesticides (OPPs) in aqueous solution and aged contaminated soil columns

Sulfidation treatment is an effective method of improving the catalytic performance of zero-valent iron (ZVI). Here, we prepared sulfidated, micro-sized ZVI (S-mZVI) using ball milling technology to activate persulfate (PS) with the goal of oxidizing organophosphorus pesticides (OPPs) in aqueous solution and aged OPP-contaminated soil columns. Energy dispersive spectroscopy (EDS), X-ray powder diffraction (XRD) and X-ray photoelectron spectrometry (XPS) analyses uncovered the formation of Fe2O3, FeOOH, FeS and FeS2 in the S-mZVI prepared by ball milling with different proportions of elemental S powder to make micro-sized ZVI particles. The presence of sulfur can regulate the morphology of S-mZVI with a dispersed and spherical shape, and it can improve the activation performance of PS. In aqueous solution, 11.2 mg of S-mZVI activated 2.5 mM PS (S-mZVI-PS) with an S/Fe molar ratio of 0.100, and it was the best at activating PS, leading to oxidation-rate constants of 0.030 s−1 for 10 mg/L phorate and 0.026 s−1 for 10 mg/L terbufos, which were much greater than those of the other S-mZVI and mZVI. The results of the soil column experiment showed that the PS, which had a low consumption for the total dosage, achieved higher degradation percentages among the three OPPs in the S-mZVI-PS treatment than those in the mZVI-PS treatment over 120 h, with the best performance achieved by oxidizing 69.7% phorate, 48.0% terbufos and 60.6% aminoparathion. The effluent concentrations of the three OPPs in the S-mZVI-PS treatment were significantly lower than those in the mZVI-PS treatment, while dissolved total iron and Fe(II) displayed the opposite results. These results indicate that S-mZVI prepared by ball milling can effectively activate PS and be applied to remediate OPP-contaminated soil.

Remediation of hexavalent chromium in column by green synthesized nanoscale zero-valent iron/nickel: Factors, migration model and numerical simulation

In this work, green tea extracts synthesized nanoscale zero-valent iron/nickel (GT-nZVI/Ni) was prepared and the Cr(VI) contaminated soil column was remediated by GT-nZVI/Ni suspension. The influence factors including the concentration, pH value and flow rate of GT-nZVI/Ni suspension were studied. Under the conditions of pH = 4, concentration of 0.15 g/L and flow rate of 1.25 mL/h, GT-nZVI/Ni suspension had the best reduction and immobilization effect on Cr(VI) in the soil column. Na+ and Ca2+ can promote the immobilization of Cr (VI) in soil, while humic acid weakened the immobilization of Cr (VI). After GT-nZVI/Ni is injected into the soil column, the content of weak acid extractable and reduced chromium is significantly reduced, and the toxic hazard of hexavalent chromium in the soil is greatly reduced. The 1D-CDE model was used to fit the breakthrough curves of Fe(tot), Fe(aq) and Fe(0), and the migration of GT-nZVI/Ni in Cr(VI) contaminated soil was simulated and predicted. Compared with the inert solute Cl-, the breakthrough curves of Fe (tot), Fe (aq) and Fe (0) in Cr (VI) contaminated soil column were significantly lagged, with delay coefficients of 2.465, 2.322 and 3.288, respectively. The reaction of GT-nZVI/Ni with Cr (VI) led to the decrease of Fe mobility. Finally, the outflow concentration of Fe (tot) was 0.064 g/L, and the loss was mainly due to reaction and retention in the soil. About 57.89% of GT-nZVI/Ni was retained in the soil.

Simultaneously enhanced surfactant flushing of diesel contaminated soil column and qualified emission of effluent

Seven surfactants were selected as candidate agents for in situ soil column flushing. Column flushing lacks the interaction between surfactants and contaminants, so efficiency is not easy to improve. Microbubbles generated in situ may adhere to the contaminant diesel. Thereafter, the bubbles were mobilized to lift the multi-system oil to the top layer. This process must be attributed to the increased column flushing efficiency of diesel removal. Compared with a single solution, using randomly methylated beta-cyclodextrin (RAMEB) and microbubble enhancement, the diesel removal of column flushing increased by 30.7%. Compared with the existing conditions (5.25 × 10−4 cm s−1), the hydraulic conductivity of loam soil (3.74 × 10−3 cm s−1) increased by 7.1 times after the continued operation of the two processes. The oil layer was collected for further reuse. After three treatments, the effluent for the RAMEB was more than 85%. The collected effluent was treated with a synthetic absorbent and then qualifiedly discharged with a TOC value of only 2.6 mg L−1. By combining surfactant flushing with microbubbles and other equipment, not only can the reaction time be effectively saved, but organic pollutants could be concentrated and reused in the soil, so no additional treatment was required.

Effect of redox variation on the geochemical behavior of Sb in a vegetated Sb(V)-contaminated soil column

This study examined the geochemical behavior of antimony (Sb) in a vegetated contaminated soil column consisting of unsaturated rhizosphere and a waterlogging layer. The results showed a reducing condition (Oxidation-Reduction Potential (ORP) of −171 mV) was formed in about 5 days in the waterlogging zone. The amount of Sb released was higher under the oxidizing unsaturated-rhizosphere compared to that in the waterlogging zone possibly because of the weaker affinity of Sb(V) to Mn- and/or Fe-oxides in soil. The fraction of Sb(III) in the dissolved total Sb increased with time when soil redox states were subjected to a further reduction. Solid phase Sb K-edge X-ray absorption spectroscopy (XAS) of soils showed that Sb(III) fraction of the deeper layer soil increased while the unsaturated upper soil solely composed Sb(V). In this study, 250 mg/kg of Sb pollution did not significantly affect plant growth and no significant transport of Sb occurred from the soil to plant. However, changes in redox conditions within the soil column induced a shift in soil microbial communities. Consequently, the importance of redox states of soil on geochemical behavior of Sb and the effects of soil flooding or waterlogging deserve attention in the management of Sb-contaminated soil.

Parameters describing nonequilibrium transport of polycyclic aromatic hydrocarbons through contaminated soil columns: Estimability analysis, correlation, and optimization

The soil and groundwater at former industrial sites polluted by polycyclic aromatic hydrocarbons (PAHs) produce a very challenging environmental issue. The description of PAH transport by means of mathematical models is therefore needed for risk assessment and remediation strategies at these sites. Due to the complexity of release kinetics and transport behavior of the PAHs in the aged contaminated soils, their transport is usually evaluated at the laboratory scale. Transport parameters are then estimated from the experimental data via the inverse method. To better assess the uncertainty of optimized parameters, an estimability method was applied to firstly investigate the information content of experimental data and the possible correlations among parameters in the two-site sorption model. These works were based on the concentrations of three PAHs, Acenaphthene (ACE), Fluoranthene (FLA) and Pyrene (PYR), in the leaching solutions of the experiments under saturated and unsaturated flow conditions. The estimability results showed that the experiment under unsaturated flow conditions contained more information content for estimating four transport parameters than under the saturated one. In addition, whatever the experimental conditions for all three PAHs the fraction of sites with instantaneous sorption, f, was highly correlated with the adsorption distribution coefficient, Kd. The very strong correlation between the two parameters f and Kd suggests that they should not be simultaneously calibrated. Transport parameters were optimized using HYDRUS-1D software with different scenarios based on the estimability analysis results. The optimization results were not always reliable, especially in the case of the experiment under saturated flow conditions because of its low information content. In addition, the estimation of transport parameters became very uncertain if two parameters f and Kd were optimized simultaneously. The findings of the current work can suggest some reasons behind the optimization problems and indicate the type of experimental information additionally needed for parameter identification. To overcome the parameterization issues of PAH non-equilibrium transport, the experimental design, timescale, and model refinement need further improvement. The conclusions presented in this paper are not limited necessarily to PAHs, but may also be relevant to other organic contaminants with similar leaching behavior.

Leaching behavior of heavy metals and transformation of their speciation in polluted soil receiving simulated acid rain.

Heavy metals that leach from contaminated soils under acid rain are of increasing concern. In this study, simulated acid rain (SAR) was pumped through columns of artificially contaminated purple soil. Column leaching tests and sequential extraction were conducted for the heavy metals Cu, Pb, Cd, and Zn to determine the extent of their leaching as well as to examine the transformation of their speciation in the artificially contaminated soil columns. Results showed that the maximum leachate concentrations of Cu, Pb, Cd, and Zn were less than those specified in the Chinese Quality Standards for Groundwater (Grade IV), thereby suggesting that the heavy metals that leached from the polluted purple soil receiving acid rain may not pose as risks to water quality. Most of the Pb and Cd leachate concentrations were below their detection limits. By contrast, higher Cu and Zn leachate concentrations were found because they were released by the soil in larger amounts as compared with those of Pb and Cd. The differences in the Cu and Zn leachate concentrations between the controls (SAR at pH 5.6) and the treatments (SAR at pH 3.0 and 4.5) were significant. Similar trends were observed in the total leached amounts of Cu and Zn. The proportions of Cu, Pb, Cd, and Zn in the EXC and OX fractions were generally increased after the leaching experiment at three pH levels, whereas those of the RES, OM, and CAR fractions were slightly decreased. Acid rain favors the leaching of heavy metals from the contaminated purple soil and makes the heavy metal fractions become more labile. Moreover, a pH decrease from 5.6 to 3.0 significantly enhanced such effects.

Remobilization of 60Co, 85Sr, 137Cs, 152Eu, and 241Am from a Contaminated Soil Column by Groundwater and Organic Ligands

The desorption rate of 60Co, 85Sr, 137Cs, 152Eu, and 241Am from soil collected from Inshas disposal site in Egypt was investigated to understand the desorption and mobility of these radionuclides in the environment. Effect of a synthetic groundwater (GW) and the GW amended to 2 × 10−5M of ethylenediaminetetraacetic acid (EDTA) or ethylenediaminediacetic acid (EDDA), GW+ETDA and GW+EDDA, respectively, was studied in flow-through experiments. These experiments were designed to compare the influence of EDTA relative to one of its degradation products that can exist in natural water, EDDA. First-order desorption and two-site first-order desorption equations were used to describe the time-dependent desorption data. The desorption rate for 85Sr and 137Cs was high in the first 50 h followed by a slow release suggesting that two different mechanisms involved. The trace metal removal was not completely reversible for all radionuclides tracers except for 85Sr. The quantity of 85Sr, 137Cs, 152Eu, and 241Am desorbed from soil follows the order GW+EDTA > GW+EDDA > GW, while 60Co gives unexpected trends where the effect of EDDA is twice as high as that of EDTA. This behavior was discussed based on the aqueous species distribution of 60Co in both aqueous solutions.

계면활성제 거품(Foam)을 이용한 토양칼럼 내 유류 및 중금속 동시 제거 연구

Simultaneous removal of heavy metals (Cd, Pb) and diesel-fuel from a soil column was evaluated by respectively flushing with sodium dodecyl sulfate (SDS) solution, mixture of SDS and sodium iodide (SDS + NaI), and surfactant foam (SDS + NaI foam). First, this study evaluated these flushing methods to the heavy metals only-contaminated soil for removal of heavy metals from the heavy-metal only contaminated soil column. After 7 pore volume flushing of the soil column, Cd removal efficiencies from the soil were 40% by SDS solution, 50% by SDS + NaI mixture, and 60% by surfactant foam. The flushing results implied that anionic surfactant and ligand can be efficiently applied to extraction of Cd from the heavy metal contaminated soil. Furthermore, surfactant foam flushing showed an increased flushing efficiency with enhancing the contact between surfactant solution and soil. However, Pb removal efficiency by these flushing methods did not show any difference unlike those of Cd. Second, this study eventually evaluated flushing methods for simultaneous removal of heavy metals and diesel-fuel from the soil column with 7 pore volume flushing. Diesel-fuel removal efficiencies were 50% by SDS + NaI flushing and 90% by SDS + NaI foam flushing. Cd removal efficiency by the foam flushing reached to 80% which was higher than the result of the previous heavy metals onlycontaminated soil experiment. This result implied that diesel-fuel could act as a metal-solvent while it contacted to heavy metals present in the soil. This study clearly showed that surfactant foam flushing simultaneously removed heavy metals and diesel fuel from the soil column.

Biosurfactant technology for remediation of cadmium and lead contaminated soils

This research focuses on column experiments conducted to evaluate the potential of environmentally compatible rhamnolipid biosurfactant produced by Pseudomonas aeruginosa strain BS2 to remove heavy metals (Cd and Pb) from artificially contaminated soil. Results have shown that di-rhamnolipid removes not only the leachable or available fraction of Cd and Pb but also the bound metals as compared to tap water which removed the mobile fraction only. Washing of contaminated soil with tap water revealed that approximately 2.7% of Cd and 9.8% of Pb in contaminated soil was in freely available or weakly bound forms whereas washing with rhamnolipid removed 92% of Cd and 88% of Pb after 36 h of leaching. This indicated that di-rhamnolipid selectively favours mobilization of metals in the order of Cd>Pb. Biosurfactant specificity observed towards specific metal will help in preferential elution of specific contaminant using di-rhamnolipid. It was further observed that pH of the leachates collected from heavy metal contaminated soil column treated with di-rhamnolipid solution was low (6.60-6.78) as compared to that of leachates from heavy metal contaminated soil column treated with tap water (pH 6.90-7.25), which showed high dissolution of metal species from the contaminated soil and effective leaching of metals with treatment with biosurfactant. The microbial population of the contaminated soil was increased after removal of metals by biosurfactant indicating the decrease of toxicity of metals to soil microflora. This study shows that biosurfactant technology can be an effective and nondestructive method for bioremediation of cadmium and lead contaminated soil.

Vertical transport of polycyclic aromatic hydrocarbons in different particle-size fractions of sandy soils

Vertical transport of selected polycyclic aromatic hydrocarbons (PAHs) in different particle-size fractions of sandy soils was investigated by simulation experiments in soil columns. Tested soil samples were fractionized into three particle-sizes including sand, coarse silt and fine silt (2,000–50, 50–20 and <20 μm). Rainfall simulations were conducted in artificially PAHs contaminated soil columns with 30 cm length and 5 cm diameter in 40 days. PAHs were extracted from soil samples and determined by high performance liquid chromatography (HPLC). Results showed that the residue level of PAHs in fine silt fraction reached 35.85 mg/kg, which was significantly higher than those in sand and coarse silt fraction (16.28 and 11.80 mg/kg, respectively), probably because PAHs in macroporous fractions were prone to volatilize or degrade compared with that in microporous fractions. Linear relationship between the residue levels of individual PAH (R PAHs) and the value of partition coefficient (log K oc) was regressed as R PAHs = 1.55 × log K oc − 5.86, R 2 = 0.91, n = 9. These results indicated that vertical transport of the mixed PAHs in soils were controlled both by the nature of PAHs (i.e. log K oc, molecular weight), soil particle size and soil organic contents, which could influence the transport of PAHs.

Bioreduction of Uranium in a Contaminated Soil Column

The bioreduction of soluble uranium [U(VI)] to sparingly soluble U(IV) species is an attractive remedial technology for contaminated soil and groundwater due to the potential for immobilizing uranium and impeding its migration in subsurface environments. This manuscript describes a column study designed to simulate a three-step strategy proposed for the remediation of a heavily contaminated site at the U.S. Department of Energy's NABIR Field Research Center in Oak Ridge, TN. The soil is contaminated with high concentrations of uranium, aluminum, and nitrate and has a low, highly buffered pH (approximately 3.5). Steps proposed for remediation are (i) flushing to remove nitrate and aluminum, (ii) neutralization to establish pH conditions favorable for biostimulation, and (iii) biostimulation for U(VI) reduction. We simulated this sequence using a packed soil column containing undisturbed aggregates of U(VI)-contaminated saprolite that was flushed with an acidified salt solution (pH 4.0), neutralized with bicarbonate (60 mM), and then biostimulated by adding ethanol. The column was operated anaerobically in a closed-loop recirculation setup. However, during the initial month of biostimulation, ethanol was not utilized, and U(VI) was not reduced. A bacterial culture enriched from the site groundwaterwas subsequently added, and the consumption of ethanol coupled with sulfate reduction immediately ensued. The aqueous concentration of U(VI) initially increased, evidently because of the biological production of carbonate, a ligand known to solubilize uranyl. After approximately 50 days, aqueous U(VI) concentrations rapidly decreased from approximately 17 to <1 mg/L. At the conclusion of the experiment,the presence of reduced solid phase U(IV) was confirmed using X-ray absorption near edge structure spectroscopy. The results indicate that bioreduction to immobilize uranium is potentially feasible at this site; however, the stability of the reduced U(IV) and its potential reoxidation will require further investigation, as do the effects of groundwater chemistry and competitive microbial processes, such as methanogenesis.

Bioremediation of Diethylhexyl Phthalate Contaminated Soil: A Feasibility Study in Slurry- and Solid-Phase Reactors

The aim of the research was to verify the possibility of applying bioremediation as a treatment strategy on a poly(vinyl chloride) (PVC) manufacturing site in the north of Italy contaminated by diethylhexyl phthalate (DEHP) at a concentration of 5.51 mg/g of dry soil. Biodegradation kinetic experiments with DEHP contaminated soil samples were performed in both slurry- and solid-phase systems. The slurry-phase results showed that the cultural conditions, such as N and P concentrations and the addition of a selected DEHP degrading strain, increased the natural DEHP degradation rate. On the basis of these data, experiments to simulate bioventing on contaminated soil columns were performed. The DEHP concentration reached 0.63 mg/g of dry soil in 76 days (89% of degradation). A kinetic equation was developed to fit the experimental data and to predict the concentration of contaminant after treatment. The data obtained are encouraging for a future in situ application of the bioventing technology.

Rhamnolipid Foam Enhanced Remediation of Cadmium and Nickel Contaminated Soil

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.

Modeling of air sparging of VOC-contaminated soil columns

Air sparging is a remediation technology currently being applied for the restoration of sites contaminated with volatile organic compounds (VOCs). Attempts have been made by various researchers to model the fate of VOCs in the gas and liquid phase during air sparging. In this study, a radial diffusion model with an air–water mass transfer boundary condition was developed and applied for the prediction of VOC volatilization from air sparging of contaminated soil columns. The approach taken was to use various parameters such as mass transfer coefficients and tortuosity factors determined previously in separate experiments using a single air channel apparatus and applying these parameters to a complex system with many air channels. Incorporated in the model, is the concept of mass transfer zone (MTZ) where diffusion of VOCs in this zone was impacted by the volatilization of VOCs at the air–water interface but with negligible impact outside the zone. The model predicted fairly well the change in the VOC concentrations in the exhaust air, the final average aqueous VOC concentration, and the total mass removed. The predicted mass removal was within 1% to 20% of the actual experimental mass removed. The results of the model seemed to suggest that air-sparged soil columns may be modeled as a composite of individual air channels surrounded by a MTZ. For a given air flow rate and air saturation, the VOC removal was found to be inversely proportional to the radius of the air channel. The approach taken provided conceptual insights on mass transfer processes during air sparging operations.

Washing of Various Lead Compounds from a Contaminated Soil Column

Soil samples artificially contaminated with 10 different lead compounds to produce 5,000 mg/kg Pb were washed with acid and ethylenediaminetetracetic acid (EDTA) solutions. For variable pH, the highest washing efficiencies were achieved at pH 2, the lowest value examined. Washing with EDTA enhanced the removal of lead, the removal increasing with an increase in the EDTA:lead molar ratio. High removals (79–106%) of adsorbed lead (as lead nitrate), lead carbonate, basic lead carbonate, lead sulfate, and lead oxide were achieved with both types of washing. Although not washed effectively with acid, significant lead dioxide removal occurred with EDTA wash. The removals of lead sulfide, lead paint, lead dimethyldithiocarbamate, and elemental lead were low (near 0–16%) under all washing conditions. The removal efficiency of the lead is affected by the compound solubility, lead solid dissolution kinetics, and lead sorption into the soil. Results clearly indicate the importance of the form of lead contamination in determining the success in determining the success of a soil washing operation. Comparison of these results with others suggests that soil washing success and soil lead bioaccessibility are related phenomena.

Washing of Cadmium(II) from a Contaminated Soil Column

The washing of cadmium (from CdO(s)) from a soil column employing either an acid solution or EDTA (a strong metal chelator) was examined. For Cd(II) levels of 50 to 1000 mg/kg, the fraction removed was essentially independent of the initial Cd(II) concentration. The most efficient washing of cadmium was achieved using an acid wash solution at pH 2.5. Lower Cd(II) removals were found at lower pH, apparently due to inhibition of CdO(s) dissolution by constituents released from the soil under highly acidic conditions. EDTA wash solutions were employed at EDTA:cadmium molar ratios ranging from 1:1 to 10:1. Up to 90% removal of total Cd(II) was achieved at the 10:1 ratio after the passage of the first 50 PV of wash solution. Although higher chelate levels enhanced Cd(II) removal, the utilization efficiency of EDTA for cadmium decreased.

Remediation of Lead Contaminated Soil by Column Extraction with EDTA: II. Modeling

Lead contamination of soils is a common problem throughout the world. Laboratory batch test and bench scale experiments have shown that EDTA can be used to remove lead from contaminated soils. However, due to the high cost and laborious task associated with actual environmental remediation of a lead contaminated soil, there is a need to be able to predict the outcome of a remediation process in advance in order to optimize the process and minimize the cost. This paper describes the development and validation of a computer model which can be used to simulate the removal of lead from a contaminated soil column using EDTA as the chelating agent. The model is able to simulate the lead removal from soil based on equilibrium as well as kinetic dissolution of Pb. The comparison of the simulated results with actual lead concentrations both in effluent and soil shows that the model can predict the lead removal process with reasonable accuracy.