Heavy metal contaminants removal by soil washing

The feasibility of soil washing for decontaminating a silty sand spiked with cadmium, chromium, lead, and zinc was evaluated in laboratory-scale batch and column experiments. Soil samples were subjected to chelant extraction using a solution of disodium salt of ethylenediaminetetraacetic acid (Na(2)EDTA), sodium metabisulfite (Na(2)S(2)O(5)) solution (an inexpensive reducing reagent), and a solution containing a mixture of the two reagents. Batch and column washing of the contaminated soil with deionized water (DI water) revealed that approximately 70% of the cadmium in the sample is weakly bound and readily mobilized in aqueous solution at neutral pH, followed by approximately 25%-30% of zinc, approximately 20%-25% chromium, and only approximately 10% of lead. Of the washing reagents tested, Na(2)EDTA solutions were generally more effective than Na(2)S(2)O(5) for removing heavy metals from the soil samples. Na(2)EDTA preferentially extracted lead over zinc and cadmium but exhibited little impact on chromium removal. Cadmium and, especially zinc, removal by a 0.01-M Na(2)EDTA solution were enhanced considerably by inclusion of 0.1 M Na(2)S(2)O(5), suggesting that a mixture of the two reagents may provide an economically optimum solution for certain contaminated soils.     

Soil washing using various nonionic surfactants and their recovery by selective adsorption with activated carbon

The performance of activated carbon in soil washing and subsequent selective adsorption for surfactant recovery from the washed solution was investigated. Sandy loam soil contaminated with phenanthrene at 200 mg kg(-1) was washed with four different nonionic surfactants: Tween 40, Tween 80, Brij 30 and Brij 35. The efficiency of soil washing was highest when using Brij 30 with the highest solubilizing ability for phenanthrene and low adsorption onto soil. In the selective adsorption step, surfactant recovery was quite effective for all surfactants ranging from 85.0 to 89.0% at 1 g L(-1) of activated carbon (Darco 20-40 mesh). Phenanthrene removal from the solution washed with Brij 30 was only 33.9%, even though it was 54.1-56.4% with other surfactants. The selectivity was larger than 7.02 except for Brij 30 (3.60). The overall performance considering both the washing and surfactant recovery step was effective when using Tween 80 and Brij 35. The results suggest that higher solubilizing ability of surfactants is a requirement for soil washing but causes negative effects on phenanthrene removal in the selective adsorption. Therefore, if a surfactant recovery process by selective adsorption is included in soil remediation by washing, the overall performance including the two steps should be considered for properly choosing the surfactant.     

Laboratory treatability testing of soils contaminated with lead and PCBs using particle-size separation and soil washing.

A soil treatability study was conducted using particle-size separation and soil washing to reduce the volume of material contaminated with polychlorinated biphenyls (PCBs) and lead at a Superfund site. Soil washing using surfactant was effective at removing 95% of PCBs into fine material and residual wash water. Results indicate that almost 80% of the material contaminated with up to 140 mg/kg PCBs could be treated to concentrations below 10 mg/kg using soil washing with surfactant. There did not appear to be a difference in lead removal using either particle size separation or soil washing, although the lead data have high uncertainty because of soil heterogeneity. Lead concentrations in soil were reduced from as high as 1700 to < or =150 mg/kg and from 560 to < or =220 mg/kg in about half of the material using particle size separation.     

Chelant extraction of heavy metals from contaminated soils.

The current state of the art regarding the use of chelating agents to extract heavy metal contaminants has been addressed. Results are presented for treatability studies conducted as worst-case and representative soils from Aberdeen Proving Ground's J-Field for extraction of copper (Cu), lead (Pb), and zinc (Zn). The particle size distribution characteristics of the soils determined from hydrometer tests are approximately 60% sand, 30% silt, and 10% clay. Sequential extractions were performed on the 'as-received' soils (worst case and representative) to determine the speciation of the metal forms. The technique speciates the heavy metal distribution into an easily extractable (exchangeable) form, carbonates, reducible oxides, organically-bound, and residual forms. The results indicated that most of the metals are in forms that are amenable to soil washing (i.e. exchangeable+carbonate+reducible oxides). The metals Cu, Pb, Zn, and Cr have greater than 70% of their distribution in forms amenable to soil washing techniques, while Cd, Mn, and Fe are somewhat less amenable to soil washing using chelant extraction. However, the concentrations of Cd and Mn are low in the contaminated soil. From the batch chelant extraction studies, ethylenediaminetetraacetic acid (EDTA), citric acid, and nitrilotriacetic acid (NTA) were all effective in removing copper, lead, and zinc from the J-Field soils. Due to NTA being a Class II carcinogen, it is not recommended for use in remediating contaminated soils. EDTA and citric acid appear to offer the greatest potential as chelating agents to use in soil washing the Aberdeen Proving Ground soils. The other chelating agents studied (gluconate, oxalate, Citranox, ammonium acetate, and phosphoric acid, along with pH-adjusted water) were generally ineffective in mobilizing the heavy metals from the soils. The chelant solution removes the heavy metals (Cd, Cu, Pb, Zn, Fe, Cr, As, and Hg) simultaneously. Using a multiple-stage batch extraction, the soil was successfully treated passing both the Toxicity Characteristics Leaching Procedure (TCLP) and EPA Total Extractable Metal Limit. The final residual Pb concentration was about 300 mg/kg, with a corresponding TCLP of 1.5 mg/l. Removal of the exchangeable and carbonate fractions for Cu and Zn was achieved during the first extraction stage, whereas it required two extraction stages for the same fractions for Pb. Removal of Pb, Cu, and Zn present as exchangeable, carbonates, and reducible oxides occurred between the fourth- and fifth-stage extractions. The overall removal of copper, lead, and zinc from the multiple-stage washing were 98.9%, 98.9%, and 97.2%, respectively. The concentration and operating conditions for the soil washing extractions were not necessarily optimized. If the conditions had been optimized and using a more representative Pb concentration (approximately 12000 mg/kg), it is likely that the TCLP and residual heavy metal soil concentrations could be achieved within two to three extractions. The results indicate that the J-Field contaminated soils can be successfully treated using a soil washing technique.     

Assessing effect of electrode configuration on the efficiency of electrokinetic remediation by sequential extraction analysis

The electroremediation experiments were conducted on artificially polluted soils by introducing a single metallic contaminant (Pb, Zn and Cu) and multiple metallic contaminants (Pb+Zn+Cu). Based on sequential extraction results, it was observed that the removal efficiencies of lead, zinc and copper vary depending on types of contamination. When the soil was contaminated only by lead, the removal efficiency was found to be 48%. However, the removal efficiency of lead decreased to 32% when the soil was contaminated by the combination of lead, zinc and copper. Similar results were observed for zinc and copper. The corresponding removal efficiency values for zinc and copper were 92% and 37%, and 34% and 31%, respectively. Effects of electrode geometry on the removal efficiency of metals were investigated by constructing a multiple anode arrangement. In this arrangement, the electrokinetic unit consists of three cylinders, which lie one inside the other, and the soil was placed in the middle cylinder. The central cylinder was the cathode well and the outer cylinder was the anode well, where eight identical anode electrodes were placed in octagonal with respect to the cathode electrode. By using this electrode arrangement in removal of metals from the soil contaminated with the combination of three metals (Pb+Zn+Cu), the removal efficiencies of lead, zinc and copper were found to be 29%, 18% and 18%, respectively. As it can be seen, these numerical values are much lower than the values that were obtained when the traditional two-plate electrode arrangement used in the electroremediation experiments (32%, 37% and 31%).     

Simultaneous removal of organic contaminants and heavy metals from kaolin using an upward electrokinetic soil remediation process

Kaolins contaminated with heavy metals, Cu and Pb, and organic compounds, p-xylene and phenanthrene, were treated with an upward electrokinetic soil remediation (UESR) process. The effects of current density, cathode chamber flushing fluid, treatment duration, reactor size, and the type of contaminants under the vertical non-uniform electric field of UESR on the simultaneous removal of the heavy metals and organic contaminants were studied. The removal efficiencies of p-xylene and phenanthrene were higher in the experiments with cells of smaller diameter or larger height, and with distilled water flow in the cathode chamber. The removal efficiency of Cu and Pb were higher in the experiments with smaller diameter or shorter height cells and 0.01M HNO(3) solution as cathode chamber flow. In spite of different conditions for removal of heavy metals and organics, it is possible to use the upward electrokinetic soil remediation process for their simultaneous removal. Thus, in the experiments with duration of 6 days removal efficiencies of phenanthrene, p-xylene, Cu and Pb were 67%, 93%, 62% and 35%, respectively. The experiment demonstrated the feasibility of simultaneous removal of organic contaminants and heavy metals from kaolin using the upward electrokinetic soil remediation process.     

Phenanthrene and pyrene oxidation in contaminated soils using Fenton's reagent

Fenton's reagent has shown its applicability to oxidizing these biorefractory organic contaminants. The purpose of this contribution was to investigate the influence of operating parameters on the process efficiency for soil highly contaminated by PAHs. Five variables were selected: pH, reaction time, UV irradiation, hydrogen peroxide concentration and Fe (II) amendment. Their effects on the oxidation of (i) phenanthrene and on (ii) phenanthrene and pyrene present in freshly contaminated soil samples were studied through batch reactor experiments following factorial designs. For phenanthrene oxidation run with a soil contaminated at 700 mg kg(-1), one set of variables enabled us to reach a residual concentration lower than 40 mg kg(-1) (Dutch legislation threshold). The most important factor was the reaction time, followed at a certain distance by UV irradiation, Fe (II), H(2)O(2) concentration and pH, this last variable being the least significant. The possibility of operating without pH adjustment is of importance in the treatment at the field scale. This shows the feasibility of photo-Fenton-like oxidation for the treatment of soil highly contaminated with PAH and the relative importance of the process variables.     

Removal of Pb by EDTA-washing in the presence of hydrophobic organic contaminants or anionic surfactant

Heavy metals and organic contaminants often coexist in contaminated soils, of which the remediation requires a combined or sequential use of surfactant and chelant in chemical-enhanced soil washing. This study investigated the Pb removal by EDTA-washing in the presence of the coexisting hydrophobic organic contaminants (marine diesel fuel, MDF) or anionic surfactant (sodium dodecyl sulfate, SDS). The results of batch experiments indicated a negative impact of MDF on Pb removal, whereas a positive or negative influence of SDS depending on the molar ratio of [EDTA]:[Pb]. The surface of MDF-contaminated soil was partially covered by free-phase MDF limiting the interaction between EDTA and sorbed Pb, especially at [EDTA]:[Pb]=1:1. Despite the ability of SDS itself for extracting Pb to some extent, probably through electrostatic interaction and dissolution of soil organic matter (SOM), the addition of SDS into EDTA solution only slightly enhanced Pb removal at [EDTA]:[Pb]=1:1 but inhibited at [EDTA]:[Pb]=2:1. This may be attributed to the SOM dissolution and the potential formation of ternary surface complexes, respectively. Along the same line of reasoning, it was not surprising that the optimal sequence for Pb removal was EDTA- followed by SDS-washing rather than the reverse sequence or simultaneous EDTA- and SDS-washing.     

Degradation of phenanthrene by bacterial strain isolated from soil in oil refinery fields in Shanghai China

A bacterial strain Pseudomonas stutzeri ZP2 was identified with phenanthrene-degrading ability based on Gram staining, oxydase reaction, biochemical tests, FAME analysis, G+C content and 16S rDNA gene sequence analysis. It is the first time that P. stutzeri is reported to process the capability for phenanthrene degradation. The strain was isolated from soil samples contaminated with polycyclic aromatic hydrocarbon (PAH)-containing waste from an oil refinery field in Shanghai, China. Strain P sp. ZP2 can utilize naphthalene, phenanthrene and Tween 80 as its sole carbon source and can degrade phenanthrene very fast, 6 days for 96% phenanthrene at 250 ppm concentration. The optimal growth conditions of strain ZP2 was determined to be at pH 8.0, 37 degrees C, respectively. The results also indicate that strain ZP2 can remove more than 90% of phenanthrene at any concentrations ranged from 250 to 1000 ppm in 6 days. It suggests that strain ZP2 can endure high concentrations of phenanthrene. Besides, the effects of non-ionic surfactants such as Brij 30, Triton X100 and Tween 80, on the phenanthrene degradation were examined. Therefore, this strain may find great application in bioremediation practices.     

Effect of ultrasound on removal of persistent organic pollutants (POPs) from different types of soils

A new and promising technology is utilization of sonochemistry on decontamination of polluted soil. The feasibility of this technology on treatment of contaminated soils (synthetic clay, natural farm clay, and kaolin) was studied by using two target persistent organic pollutants (POPs): hexachlorobenzene (HCB) and phenanthrene (PHE). The soils were highly contaminated in 500 mg/kg. The laboratory experiments were conducted with various conditions (moisture, power, and time duration). The effects of these parameters on ultrasonication (as well as the removal of contaminants) were examined. The reasonable moisture ratio of the slurry could be in range of 2:1–3:1. The process did not change pH values of soils. Experimental results showed that ultrasonication has a potential to reduce the high concentrations of these POPs.     

Heavy metal removal from sediments by biosurfactants.

Batch washing experiments were used to evaluate the feasibility of using biosurfactants for the removal of heavy metals from sediments. Surfactin from Bacillus subtilis, rhamnolipids from Pseudomonas aeruginosa and sophorolipid from Torulopsis bombicola were evaluated using a metal-contaminated sediment (110mg/kg copper and 3300mg/kg zinc). A single washing with 0.5% rhamnolipid removed 65% of the copper and 18% of the zinc, whereas 4% sophorolipid removed 25% of the copper and 60% of the zinc. Surfactin was less effective, removing 15% of the copper and 6% of the zinc. The technique of ultrafiltration and zeta potential measurements were used to determine the mechanism of metal removal by the surfactants. It was then postulated that metal removal by the biosurfactants occurs through sorption of the surfactant on to the soil surface and complexation with the metal, detachment of the metal from the soil into the soil solution and hence association with surfactant micelles. Sequential extraction procedures were used on the sediment to determine the speciation of the heavy metals before and after surfactant washing. The carbonate and oxide fractions accounted for over 90% of the zinc present in the sediments. The organic fraction constituted over 70% of the copper. Sequential extraction of the sediments after washing with the various surfactants indicated that the biosurfactants, rhamnolipid and surfactin could remove the organically-bound copper and that the sophorolipid could remove the carbonate and oxide-bound zinc. Therefore, heavy metal removal from sediments is feasible and further research will be conducted.     

Isolation and characterization of phenanthrene-degrading strains Sphingomonas sp. ZP1 and Tistrella sp. ZP5

Two bacteria strains Sphingomonas sp. strain ZP1 and Tistrella sp. strain ZP5 were identified as phenanthrene-degrading ones, based on Gram staining, oxydase reaction, biochemical tests, FAME analysis, G+C content and 16S rDNA gene sequence analysis. We isolated these two bacteria strains Sphingomonas sp. ZP1 and Tistrella sp. ZP5 from soil samples contaminated with polycyclic aromatic hydrocarbon (PAH)-containing waste from oil refinery field in Shanghai, China. Strain Sphingomonas sp. ZP1 was able to degrade naphthalene, phenanthrene, toluene, methanol and ethanol, salicylic acid and Tween 80. Moreover, it can remove nearly all the phenanthrene at 0.025% concentration in 8 days. Strain Tistrella sp. ZP5 cannot degrade phenanthrene individually but it can increase the speed of phenanthrene degradation together with ZP1. The growth conditions of strain Sphingomonas sp. ZP1 were optimized. The result also indicated that the degradation rate of phenanthrene ranged from 250 to 1000 ppm with strain ZP1 remained nearly the same, i.e., a high concentration of phenanthrene did not inhibit both the growth of microbial strains and the phenanthrene-degradation ability. Besides, the effect of non-ionic surfactants such as Brij 30, Triton X-100 and Tween 80 on the phenanthrene degradation was determined. Such two strains may be useful for bioremediation applications.     

Use of biosurfactant to remediate phenanthrene-contaminated soil by the combined solubilization-biodegradation process

The applicability of the combined solubilization-biodegradation process was examined using soil-packed column. In the solubilization step, 50 pore volumes of 150 mg/l biosurfactants solution was injected and the percentage removal of phenanthrene (mg) was 17.3% and 9.5% from soil with pH 5 and 7, respectively. The highest solubility was detected at pH 5 and this result confirmed that adjusting the pH of the biosurfactants solution injected could enhance the solubility of phenanthrene. Following this, soil samples were completely transferred to batches and incubated for 10 weeks to monitor phenanthrene degradation. The phenanthrene concentration in the soil samples decreased significantly during the biodegradation step in all soil samples, except for the soil sample that was flushed with biosurfactants solution with pH 4. This indicated that the degradation of contaminants by specific species might not be affected by the residual biosurfactants following application of the solubilization process. Moreover, these results suggested that the biosurfactant-enhanced flushing process could be developed as a useful technology with no negative effects on subsurface environments and could be combined with the biodegradation process to increase the removal efficiency.     

Remediation of Pb-contaminated soils by washing with hydrochloric acid and subsequent immobilization with calcite and allophanic soil

Removal of heavy metals from contaminated soil is not popular because of its high cost. Reducing the bioaccessible heavy metals content to an allowable level by washing with inorganic acids and subsequent immobilization of remained metals may be a low cost option for soil remediation. The applicability of this combined treatment was investigated using three different types of soil, a kaolinitic, a smectitic and an allophanic soil, which were artificially contaminated with Pb. The effectiveness of the treatment was evaluated using two main criteria: (i) reduction of the HCl extractable Pb (bioaccessible Pb) below 150 mg kg(-1), reduction of water extractable Pb below the concentration of 0.01 mg L(-1). These values correspond to allowable levels suggested by the Japanese Ministry of Environment. The soils were washed batch-wise at a solution to soil ratio of 5 L kg(-1) successively with 1 mol L(-1) HCl and 0.1 mol L(-1) CaCl(2) solutions. The two solutions were separated by filtration from one batch and reused for washing the next batch of soil without processing. The Pb concentration in the solutions increased after repeated use and removal efficiency gradually declined. The efficiency of the treatment was highly dependent on the type of soil. In the kaolinitic soil, HCl extractable Pb content of the soil from the first batch was about 50 mg kg(-1) and it exceeded 150 mg kg(-1) in that from sixth batch. But the combined soils from 1st to 10th batches gave bioaccessible Pb content barely below 150 mg kg(-1). For the smectitic soil having higher cation exchange capacity, the acceptable number of times of reuse was estimated to be 4. For the allophanic soil, treatment with the HCl solution was efficient only for the first batch of the soil, and the reuse of the acid solution was found to be ineffective. The application of 50 g kg(-1) of calcite or slacked lime was effective for reducing the water extractable Pb content. To keep soil pH near neutral and secure long term stability, the application of 50 g kg(-1) of calcite and 100 g kg(-1) of allophanic soil was chosen as the best method. This combination of amendments could reduce the water extractable Pb to almost undetectable levels after 3 days of aging.     

Removal of contaminant metals from fine grained soils, using agglomeration, chloride solutions and pile leaching techniques

A leaching process based on the use of a HCl-CaCl2 solution, with total chloride concentration 4M, was investigated for the removal of contaminant metals from fine acidic soils. The possibility to apply this treatment on piles constructed on-site was also examined as a low cost treatment option. The soil sample used in the study was fine in texture, i.e. clay loam, acidic (pH 5.6), and contaminated mainly with Pb, up to 16000mg Pb/kg dry soil, due to past mining activities. The experimental work comprised all the treatment stages, including agglomeration of fine soil particles to increase the permeability of soil, leaching of the agglomerated soil in a laboratory column, removal of metals from the leachate, regeneration and recycling of the leaching solution and final washing of the treated soil. The initial agglomeration treatment resulted in the formation of coarse aggregates and the percolation of leaching solution through the soil column was maintained at high levels, i.e.75ml/cm(2) per day, during the whole treatment. A low amount of HCl acid was required for the removal contaminants from this particular soil, i.e. 0.44mol HCl/kg soil, due to the absence of acid consuming minerals. The extractions achieved were 94% for Pb, 78% for Zn and more than 70% for Cd. The co-dissolution of soil matrix was very limited, with a total weight loss about 3.5%. The final pH of the soil after washing was found to be 5.15, i.e. slightly lower compared to the initial pH of the soil. The results of this study indicate that chloride leaching, in combination with agglomeration and pile leaching techniques, can be a cost effective option for the removal of metal contaminants from fine acidic soils.     

Enhanced solubilization and removal of naphthalene and phenanthrene by cyclodextrins from two contaminated soils

The development of innovative methods for cleaning contaminated soils has emerged as a significant environmental priority. Herein, are investigated the effectiveness of cyclodextrin (CD) to solubilize and to extract organic pollutants from soils. The interactions in the cyclodextrin/pollutant/soil system have been studied "step by step" using two kinds of polycyclic aromatic hydrocarbons (PAH), naphthalene (Nap) and phenanthrene (Phe), cyclodextrins and soils. Inclusion complex formation of PAH with beta-cyclodextrin (beta-CD) and hydroxypropyl-beta-cyclodextrin (HPCD) has been investigated and was proposed as a way to facilitate the pollutant removal from soil. Little effect of ionic strength was observed on CD complex formation for both compounds. The solubility of PAH in 50 g L(-1) of HPCD was enhanced 20- and 90-fold for naphthalene and phenanthrene, respectively. Batch experiments were performed to study the adsorption-desorption of two PAH on two soils and the influence of CDs over these processes. These experiments were also conducted with a mixture of two PAH. The batch desorption results indicate that removal capacity of HPCD was higher than that of beta-CD. Phenanthrene was strongly sorbed on soils, this led to low desorption rates compared to that of naphthalene, whatever the extracting agent used. When HPCD solution was used as a flushing agent, 80% of naphthalene and 64% of phenanthrene recovery from soil were observed. For both compounds, the slowest desorption rate was found for the soil that had the greatest content of organic matter. CD sorption on soils, was relatively low and depended on soil type. The soil organic matter (SOM) could favor the retention of both CD and pollutant involving the extraction rate to be decreased. A competitive hydrophobic interactions of pollutant between SOM and CD molecules, and co-sorption were expected to be the mechanism for the inhibited desorption.     

Electroosmotic flow behaviour of metal contaminated expansive soil

It is important to study the flow behaviour through soil during electrokinetic extraction of contaminants to understand their removal mechanism. The flow through the expansive soil containing montmorillonite is monitored during laboratory electrokinetic extraction of heavy metal contaminants. The permeability of soil, which increases due to the presence of contaminants, is further enhanced during electrokinetic extraction of contaminants due to osmotic permeability. The variations in flow rates through the soil while the extracting fluid is changed to dilute acetic acid (used to control the increase of pH) and EDTA solution (used to desorb the metal ions from soil) are studied. The trends of removal of contaminants vis-a-vis the changes in the flow through the soil during different phases of electrokinetic extraction are established. Chromium ions are removed by flushing of water through the soil and increased osmotic flow is beneficial. Removal of iron ions is enhanced by induced osmotic flow and desorption of ions by electrokinetic processes.     

Electrochemical EDTA recycling after soil washing of Pb, Zn and Cd contaminated soil

Recycling of chelant decreases the cost of EDTA-based soil washing. Current methods, however, are not effective when the spent soil washing solution contains more than one contaminating metal. In this study, we applied electrochemical treatment of the washing solution obtained after EDTA extraction of Pb, Zn and Cd contaminated soil. A sacrificial Al anode and stainless steel cathode in a conventional electrolytic cell at pH 10 efficiently removed Pb from the solution. The method efficiency, specific electricity and Al consumption were significantly higher for solutions with a higher initial metal concentration. Partial replacement of NaCl with KNO₃ as an electrolyte (aggressive Cl⁻ are required to prevent passivisation of the Al anode) prevented EDTA degradation during the electrolysis. The addition of FeCl₃ to the acidified washing solution prior to electrolysis improved Zn removal. Using the novel method 98, 73 and 66% of Pb, Zn and Cd, respectively, were removed, while 88% of EDTA was preserved in the treated washing solution. The recycled EDTA retained 86, 84 and 85% of Pb, Zn and Cd extraction potential from contaminated soil, respectively.     

Electrokinetic movement of hexachlorobenzene in clayed soils enhanced by Tween 80 and beta-cyclodextrin

This study describes the comparative behavior of hexachlorobenzene (HCB) contaminated clayed soils in an electrokinetic (EK) system enhanced by Tween 80 and beta-cyclodextrin (beta-CD). The pH of the soils was controlled by Na2CO3/NaHCO3 buffer. Negligible HCB movement was observed when NaOH or Na2CO3/NaHCO3 buffer was used as anodic flushing solution. While Tween 80 or beta-CD was introduced to Na2CO3/NaHCO3 buffer, obvious HCB movement was achieved. Although beta-CD led to a less desorption of HCB from kaolin than Tween 80, the removal of HCB with beta-CD was much higher than that with Tween 80 in the EK system. Tween 80 could be sorped by kaolin more than beta-CD, which was responsible for the result. The mechanism of the movement of HCB was proposed as the enhanced desorption of HCB from soil, the dissolving of HCB in the soil pore fluid and the movement of HCB with the electroosmotic flow. Obvious movement of HCB was also observed in the EK treatment of real HCB-contaminated clayed soil enhanced by beta-CD. It is an alternative approach to use facilitating agents such as beta-CD to enhance the EK movement of HCB in the contaminated clayed soils.     

Removal of lead and zinc ions from water by low cost adsorbents

In this study, activated carbon, kaolin, bentonite, blast furnace slag and fly ash were used as adsorbent with a particle size between 100 mesh and 200 mesh to remove the lead and zinc ions from water. The concentration of the solutions prepared was in the range of 50–100 mg/L for lead and zinc for single and binary systems which are diluted as required for batch experiments. The effect of contact time, pH and adsorbent dosage on removal of lead and zinc by adsorption was investigated. The equilibrium time was found to be 30 min for activated carbon and 3 h for kaolin, bentonite, blast furnace slag and fly ash. The most effective pH value for lead and zinc removal was 6 for activated carbon. pH value did not effect lead and zinc removal significantly for other adsorbents. Adsorbent doses were varied from 5 g/L to 20 g/L for both lead and zinc solutions. An increase in adsorbent doses increases the percent removal of lead and zinc. A series of isotherm studies was undertaken and the data evaluated for compliance was found to match with the Langmuir and Freundlich isotherm models. To investigate the adsorption mechanism, the kinetic models were tested, and it follows second order kinetics. Kinetic studies reveals that blast furnace slag was not effective for lead and zinc removal. The bentonite and fly ash were effective for lead and zinc removal.