Electrokinetic Treatment Research Articles

The transport behavior of As, Cu, Pb, and Zn during electrokinetic remediation of a contaminated soil using electrolyte conditioning

Electrokinetic remediation (also known as electrokinetics) is a promising technology for removing metals from fine-grained soils. However, few studies have been conducted regarding the transport behavior of multi-metals during electrokinetics. We investigated the transport of As, Cu, Pb, and Zn from soils during electrokinetics, the metal fractionation before and after electrokinetics, the relationships between metal transport and fractionation, and the effects of electrolyte conditioning. The main transport mechanisms of the metals were electroosmosis and electromigration during the first two weeks and electromigration during the following weeks. The direction of electroosmotic flow was from the anode to the cathode, and the metals in the dissolved and reducible-oxides fractions were transported to the anode or cathode by electromigration according to the chemical speciation of the metal ions in the pore water. Moreover, a portion of the metals that were initially in the residual fraction transitioned to the reducible and soluble fractions during electrokinetic treatment. However, this alteration was slow and resulted in decreasing metal removal rates as the electrokinetic treatment progressed. In addition, the use of NaOH, H3PO4, and Na2SO4 as electrolytes resulted in conditions that favored the precipitation of metal hydroxides, phosphates, and sulfates in the soil. These results demonstrated that metal removal was affected by the initial metal fractionation, metal speciation in the pore solution, and the physical–chemical parameters of the electrolytes, such as pH and electrolyte composition. Therefore, the treatment time, use of chemicals, and energy consumption could be reduced by optimizing pretreatment and by choosing appropriate electrolytes for the target metals.

A study on electrokinetic dewatering of oil sands tailings

Oil sands tailings (mature fine tailing (MFT)) are the final product of oil sands processing and are in the form of slurry with a very low solid content. After sedimentation, due to a low hydraulic conductivity of the tailings, dewatering and consolidating the tailings is difficult. Since electrokinetics (EK) has been successfully applied on dewatering and consolidation of low permeability soils, this study is carried out to assess the effectiveness and efficiency of EK dewatering of MFT, a man-made geomaterial. Two series of tests were conducted in this study. In the first series, four EK cell tests were performed on oil sands tailings to measure the electroosmotic permeability, ke, which is the key parameter for assessment of the EK treatment. In the second series, the model tests were designed and carried out to investigate the feasibility of EK dewatering on oil sands tailings. The performance of the EK dewatering was compared under two conditions — under a surcharge load of 5 kPa for consolidation, followed by EK dewatering and under simultaneous treatment of a surcharge load of 5 kPa and EK treatment. The final water content, undrained shear strength and plasticity of MFT were measured after all tests. It was observed that the EK dewatering model tests resulted in significant overall increases in the undrained shear strength and reductions in the water content of tailings samples, along with significant changes of the tailings plasticity.

펄스동전기법과 연속처리동전기법을 이용한 점토성-사질토의 탈수화 효율 비교

펄스동전기법은 점토성-사질토에서 탈수화 공정을 효율적으로 진행하기 위해 제안되었다. 제안된 동전기법은 점토성-사질토에서 토양 안정성의 증진을 위해 전류 흐름에 따르는 유체의 이동에 의한 탈수화 공정을 진행하는 것이다. 제안된 동전기법의 성능을 확인하기 위해 제작된 샘플은 총 7일간에 점진적으로 압력을 증가시켜 30 psi(<TEX>$2.11kgf/cm^2$</TEX>)의 최종압력으로 압축과정을 거쳐 완성되었다. 기존의 연속적인 처리와 펄스방식으로 처리하는 공정을 비교하여 각각의 특성을 관찰하였다. 각각의 테스트는 48시간 동안 3 V/cm의 전압 경사 조건으로 연속적인 처리공정과 48시간 동안 총 8시간씩 3회에 걸쳐 전기를 차단하는 펄스방식으로 진행하였다. 그 결과, 펄스방식의 효율이 연속처리방식의 효율과 비슷한 것으로 나타났고 펄스방식이 연속처리방식보다 전력소비가 약 50 % 감소로 그 경제성을 입증하였다. Pulse electrokinetic technology is proposed for improving the dewatering-process from clay-sandy soil. Proposed electrokinetic technology is to be the dewatering process due to fluid movement of current flow for the stability of clay-sandy soils. Samples produced in this study were completed to verify the proposed performance for 7 days by gradually increasing the pressure to the final pressure of 30 psi (<TEX>$2.11kgf/cm^2$</TEX>) through the compression process. In this study, pulse electrokinetic treatment and conventional continuous electrokinetic treatment are tested and observed, respectively. The condition of continuous electrokinetic treatment is a continuous process during 48 hours. And the condition of pulse electrokinetic treatment system is to interrupt the power three times for 48 hours, every 8 hours. These treatments are that the voltage gradient is 3 V/cm. As a result, the efficiency of pulse electrokinetic is similar to the continuous electrokinetic. The power consumption efficiency of pulse electrokinetic is better than continuous electrokinetic.

전기동력학 기술을 이용한 시설재배지 토양 염류제거 실증 연구

본 연구에서는 높은 농도의 염류가 집적된 시설재배지 토양의 제염을 위해 전기동력학적(EK) 기술을 적용한 파일럿 규모(<TEX>$2{\times}3{\times}0.2m^3$</TEX>, <TEX>$W{\times}L{\times}D$</TEX>)의 실증시험을 실시하였다. 실험 전 토양의 전기전도도(EC)는 약 9 dS/m였으며, 토양내 주요 염류는 <TEX>$Ca^{2+}$</TEX>, <TEX>$Cl^-$</TEX>, <TEX>$SO_4^{2-}$</TEX> 이온이었다. 2주간의 EK 처리 후 토양의 EC는 실험 전에 비해서 52% 감소하였으며, 이 중 대부분은 초기 1주일 이내에 제거되었다(47%). 이는 주로 <TEX>$Na^+$</TEX>와 <TEX>$Cl^-$</TEX>의 제거에 의한 것으로 보이며, 주요 염류 이자 토양에 대해 높은 흡착능을 가지는 <TEX>$Ca^{2+}$</TEX>와 <TEX>$SO_4^{2-}$</TEX>이온은 상대적으로 제거율이 낮았다. EK 실험이 진행되는 동안 토양의 온도는 전류의 세기에 따라 증가하여 최대 <TEX>$50^{\circ}C$</TEX>까지 증가하였다. 따라서 작물이 재배 중인 토양의 원위치 EK 적용을 위해서는 토양의 온도 상승을 제한하기 위해 전류를 조절할 필요가 있다. 결론적으로 EK 기술을 이용하여 경작 중이거나 휴경 중인 시설재배지 토양의 원위치 염류 제거가 가능할 것으로 판단되며 효율적인 탈염을 위해서는 적절한 운전 전략이 요구된다. A pilot-scale electrokinetic (EK) separation field test (<TEX>$2{\times}3{\times}0.2m^3$</TEX>, <TEX>$W{\times}L{\times}D$</TEX>) was performed in a greenhouse to remove salts from saline soil. Initially, the greenhouse soil had high electrical conductivity (EC), about 9 dS/m, and contained mainly <TEX>$Ca^{2+}$</TEX>, <TEX>$Cl^-$</TEX> and <TEX>$SO_4^{2-}$</TEX> ions. After 2 weeks of EK treatment, the soil EC was reduced to 52% compared with its initial value. The EC reduction was mostly achieved within the first week (47%) due to removal of <TEX>$Na^+$</TEX> and <TEX>$Cl^-$</TEX> ions, but ions with a high adsorption capacity such as <TEX>$Ca^{2+}$</TEX> and <TEX>$SO_4^{2-}$</TEX> ions were difficult to be removed. During the EK test, the soil temperature increased and it reached around <TEX>$50^{\circ}C$</TEX> at some regions. For in situ application to soils in cultivation, the current should be controlled to limit increases in temperature, especially near the cathodes. In conclusion, the in situ EK technique is feasible for the restoration of saline greenhouse soils in or no cultivation and an appropriate strategy is necessary for more effective remediation.

Electrokinetic stabilization of heavy metals in MSWI fly ash after water washing

This study assessed the feasibility of combining the water washing and electrokinetic (EK) treatments for the removal of Pb, Cd, Cr, and Cu from two municipal solid waste incineration (MSWI) fly ashes. Two approaches were compared: a direct electrokinetic (DEK) treatment and a combined method using water washing before the electrokinetic (WEK) treatment. The following experimental EK parameters were evaluated: electric current, pH, and treatment time (168 h). The analytical results from a toxicity characteristic leaching procedure (TCLP) showed that one fly ash sample was within the regulatory limits after either approach. However, the second fly ash sample was only within the limits following the WEK technique because the WEK technique was able to decrease the high Pb level of 58.6% in the exchangeable and carbonates fractions to 9.5% in this sample. The water washing step first extracted the soluble salts KCl, NaCl, SiCl4, and CaClOH and decreased the interference from the large chloride concentration, thereby promoting the ability of the subsequent EK treatment to stabilize heavy metals as less reactive complexes. Therefore, the WEK technique is recommended over the DEK technique for treating fly ash. © 2014 American Institute of Chemical Engineers Environ Prog, 33: 1235–1241, 2014

LABORATORY EVALUATION OF PHYSICO-CHEMICAL VARIATIONS IN BENTONITE UNDER ELECTROKINETIC ENHANCEMENT

When the traditional ground improvement techniques are not practical for a particular situation, alternative technology, such as electrokinetic (EK) soil treatment can be considered. EK treatment method involves applying a low direct current (DC) or a low potential gradient to arrays of electrodes inserted in the low permeable soils simulating migration of electricity, pore water, ions and charged particles across the soil, hence modifying the physicochemical, mechanical and engineering properties of the soil. This study investigates the effects of EK treatment on conductance phenomena and physico-chemical changes of bentonite at different intervals under total applied voltage of 10V subjected to specific types of anode enhancement solutions. The cumulative electroosmotic flow and electric current through the sample was measured for 15 days of treatment. The specimens were also tested for moisture content, pH and undrained shear strength variations over different time periods of 3, 6, 9, 12 and 15 days showing good correlations between the soil parameters. across the soil. The combined effects of these processes together with various geochemical reactions alter the chemical composition of the soil porous medium and hence modify the physicochemical properties of the soil during the EK

Novel Fusion Electrokinetic Technology with Gas Re-Injection (GREK) for Soil Remediation and Stabilization

In this study, a gas reinjection type electrokinetic remediation treatment process (GREK) was proposed as the method for the restoration and stabilization of contaminated soil. The proposed electrokinetic remediation was a new technique, where treatment was performed by reinjecting the surplus gas, which was produced from an anode chamber, into soil, in order to remove the heavy metals and moisture that exist in clayey soil or clayey-sandy soil with low hydraulic conductivity. The manufactured samples were completed through the compression process, in which pressure was gradually increased to a final pressure of 2.11 kgf/cm2 (30 psi) during a total of 7 days. Before the compression, the samples were taken, and the heavy metal concentration and water content were measured. For the gas reinjection type electrokinetic remediation treatment process (GREK) and non-injection type treatment method, continuous treatment processes were performed for 24 hours at a voltage gradient of 2 V/cm. The results of the water content indicated that the gas reinjection type electrokinetic remediation treatment process (GREK) was about 3% higher than that for non-injection type treatment method. The removal efficiency of chromium (Cr)indicated that the gas reinjection type electrokinetic remediation treatment process (GREK) was about 15% higher than that for non-injection type treatment method. The removal efficiency of cadmium (Cd) indicated that the gas reinjection type electrokinetic remediation treatment process (GREK) was about 22% higher than that for non-injection type treatment method. It is expected that the proposed gas reinjection type treatment method would contribute to convergence electrokinetic treatment processes in the future.

Sequential application of chelating agents and innovative surfactants for the enhanced electroremediation of real sediments from toxic metals and PAHs

This study focused on the sequential application of a chelating agent (citric acid) followed by a surfactant in the simultaneous electroremediation of real contaminated sediments from toxic metals and Polycyclic Aromatic Hydrocarbons (PAHs). Furthermore, the efficiency evaluation of two innovative non-ionic surfactants, commercially known as Poloxamer 407 and Nonidet P40, was investigated. The results indicated a removal efficacy of approximately 43% and 48% for the summation of PAHs (SUM PAHs), respectively for the aforementioned surfactants, much better than the one obtained by the use of Tween 80 (nearly 21%). Individual PAHs (e.g. fluorene) were removed in percentages that reached almost 84% and 92% in the respective electrokinetic experiments when these new surfactants were introduced. In addition, the combined-enhanced sequential electrokinetic treatment with citric acid improved dramatically the removal of Zn and As, compared to the unenhanced run, but did not favor the other toxic metals examined. Since no improvement in metal removal percentages occurred when Tween 80 was used, significant contribution to this matter should also be attributed to the solubilization capacity of these innovative, in electrokinetic remediation, non-ionic surfactants.

Electrokinetic Treatment of Cr-, Cu-, and Zn-Contaminated Sediment: Cathode Modification

Enhanced electrokinetic (EK) removal of Cr, Cu, and Zn from sediment by using original and modified integrated ion exchange (IIX™) cathodes was investigated. IIX cathode design and EK device process modifications were made to improve performance: separation of IIX cathode components (IIXS), combination of modified IIX cathode with pulsed electric field (IIXSP), and separation of IIX cathode components with addition of an anion exchange resin compartment (IIXA). After using the IIXSP, overall Cr, Cu, and Zn removal efficacies were significantly improved compared with the other treatments investigated. No improvements in overall Cr, Cu, and Zn removal efficacies were achieved by utilization of IIXA. Nevertheless, significant removal efficacies occurred at the anode region since distribution of the alkaline front was prevented. However, metal accumulation in the cathode region occurred. This was a consequence of metal cation complexation with Cl- released from the anion exchange resin that changed the direction of metal migration. Enhancing EK remediation of Cr-, Cu-, and Zn-contaminated sediment can be achieved by using a modified IIX cathode.

Electroremediation of a natural soil polluted with phenanthrene in a pilot plant

In this work, a pilot plant with two rows of three electrodes in semipermeable electrolyte wells was used to study the electrokinetic treatment of a natural soil polluted with phenanthrene (PHE). The electrokinetic pilot plant was an open system, i.e., there was direct contact between the soil and air. To increase the solubility of phenanthrene, thereby enhancing its transport through the soil, an aqueous solution of the anionic surfactant dodecyl sulfate was used as a flushing fluid. The results show that at the pilot scale considered, gravity and evaporation fluxes are more relevant than electrokinetic fluxes. Contrary to observations at the laboratory scale, desorption of PHE promoted by electric heating appears to be a significant removal mechanism at the pilot scale. In addition, PHE is dragged by the electroosmotic flow in the cathodic wells and by electrophoresis after interaction of the surfactant with phenanthrene in the anodic wells. In spite of the long treatment time (corresponding to an energy consumption over 500kWhm−3), the average removal attained was only 25%.

Effects of electrokinetic treatment of contaminated sludge on migration and transformation of Cd, Ni and Zn in various bonding states

This study assesses the effect of electrokinetic processes on the migration and bonding states of various heavy metals in municipal sludge. The transformation and migration are discussed through the examination of sludge characteristics and distribution of Cd, Zn and Ni after electrokinetic treatments. The migration and distribution of the contaminants after the electrokinetic treatments were determined for each sludge sample by sequential extraction. The noticeable changes on the average speciation fractions of Cd, Zn and Ni were observed that oxidizable heavy metals increased and reducible fraction decreased due to the application of voltage. Bivariate correlation analysis indicated that the amounts of different bonding states of Zn and Ni were significantly correlated (P<0.05) with durations and resistance. The oxidizable Zn was negatively correlated with exchangeable and reducible Zn. Moreover, reducible Zn had a close negative relationship with residual Zn. The bonding state of Ni was significantly related to the durations of electrokinetic processes, indicating the existing of mutual transformation between different speciation fractions over time. The analysis also indicated that the exchangeable Cd showed a close negative relationship with reducible Cd (P<0.01), whereas the reducible Cd was negatively related to residual Cd (P<0.05).

Remediation of soil co-contaminated with petroleum and heavy metals by the integration of electrokinetics and biostimulation

Successful remediation of soil co-contaminated with high levels of organics and heavy metals is a challenging task, because that metal pollutants in soil can partially or completely suppress normal heterotrophic microbial activity and thus hamper biodegradation of organics. In this study, the benefits of integrating electrokinetic (EK) remediation with biodegradation for decontaminating soil co-contaminated with crude oil and Pb were evaluated in laboratory-scale experiments lasting for 30 days. The treated soil contained 12,500mg/kg of total petroleum hydrocarbons (TPH) and 450mg/kg Pb. The amendments of EDTA and Tween 80, together with a regular refreshing of electrolyte showed the best performance to remediate this contaminated soil. An important function of EDTA-enhanced EK treatment was to eliminate heavy metal toxicity from the soil, thus activating microbial degradation of oil. Although Tween 80 reduced current, it could serve as a second substrate for enhancing microbial growth and biodegradation. It was found that oil biodegradation degree and microbial numbers increased toward the anode and cathode. Microbial metabolism was found to be beneficial to metal release from the soil matrix. Under the optimum conditions, the soil Pb and TPH removal percentages after 30 days of running reached 81.7% and 88.3%, respectively. After treatment, both the residual soil Pb and TPH concentrations met the requirement of the Chinese soil environmental quality standards.

Removal of fluorine from contaminated soil by electrokinetic treatment driven by solar energy

Instead of direct current power supply, a series of electrokinetic remediation experiments driven by solar energy on fluorine-contaminated soil were conducted in a self-made electrolyzer, in order to reduce energy expenditure of electrokinetic remediation. After the 12-day electrokinetic remediation driven by solar energy, the removal efficiency of fluorine was 22.3%, and electrokinetic treatment had an impact on changes in partitioning of fluorine in soil. It proved that the combination of electrokinetics and solar energy was feasible and effective to some extent for the remediation of fluorine-contaminated soil. Meanwhile, the experimental results also indicated that the electromigration was a more dominant transport mechanism for the removal of fluorine from contaminated soil than electroosmosis, and the weather condition was the important factor in affecting the removal efficiency.

Marble protection: An inorganic electrokinetic approach

The influence of an electric potential difference in an aqueous solution was studied as a method for depositing a calcium oxalate coating over a weathered carbonatic stone. Samples of weathered Carrara white marble were treated at 15 and 50°C for 5h in an electrokinetic cell, specifically conceived for this study, containing a solution of ammonium oxalate (4% by weight), and were subsequently characterised by scanning electron microscopy, X-ray diffractometry, thermogravimetric analysis and mercury intrusion porosimetry. The electrokinetic treatment proved to be a cost effective and time saving process, able to produce a thick and homogeneous calcium oxalate coating over the stone surface that improves its chemical and physical resistance in low pH environments, and is able to protect the stone from the by-products of urban pollution.

Improving the Electrokinetic Remediation of Nickel-, Cadmium-, and Lead-contaminated Sediment

In this work, the simultaneous application of bipolar electrodes and a longer cathodic compartment length without agents addition was used as an enhanced electrokinetic treatment of Ni-, Cd-, and Pb-contaminated sediment. Conventional and enhanced treatments were investigated and their efficacy assessed by comparing the residual metals content in the sediment with values given by Dutch standards. After conventional treatment removals of 20%, 19%, and 31% for Ni, Cd, and Pb were achieved, whereas the enhanced treatment achieved removal efficacies of 36% for Ni, 42% for Cd, and 43% for Pb. Results indicate that the simultaneous application of the techniques mentioned is effective for removing Ni and Pb whereas Cd was not removed to the desired level. Here we show that the addition of chemicals is not necessary to increase the efficacies of electrokinetic sediment treatments, so the simultaneous application of the techniques mentioned can be described as environmentally friendly.

Zeta Potentials of Suspended Humus in Multivalent Cationic Saline Solution and Its Effect on Electro-Osomosis Behavior

The surface electrical charge was measured for laboratory grade organic soil colloidal particles by varying pH between 2 and 11 and at 0.001, 0.01, 0.1, and 1.0 mol/L of cationic saline solution (CaCl2, Na2Sio3, Al2(SO4)3, MgCl2, and Na2CO3) concentrations. The zeta (ζ) potential values showed low sensitivity to pH in salt solutions. The ζ potential of pure organic soils varied from +7.5 mV at pH 2.8 to −28.5 mV at pH 11.3. The ζ potential calculation of humus particles in distilled water showed an increase in ζ potential value beyond pH > 3.3, which could be due to charge development at the humic substances by direct transfer of H+ from organic soil to water. The surface electrical charge was almost zero at pH 3.25. Colloidal charge reversal was observed at several stages according to the electrolyte concentrations and chemical reagents. It was also found that using high molarities of multivalent saline solution (e.g., CaCl2, Na2Sio3, Na2CO3, and MgCl2) as electrolytes led to very high ζ potential values and consequently high electro-osmotic conductivity (Ke). On the basis of the results of this research, it is recommended that the ζ potential of the soils be determined before any application of electrokinetic (EK) treatment.

In Situ Electrokinetic Removal of Salts from Greenhouse Soil Using Iron Electrode

An electrokinetic (EK) field study was performed on a pilot scale (2.2 × 3.3 × 0.3 m3, W × L × D) in a greenhouse by using Fe electrodes and bentonite backfill. When a constant voltage gradient was applied, the current intensity was affected by electrode position, and the soil temperature increased with the current intensity. After the EK treatment, the soil pH was little changed and the cations were hardly removed because of the ion exchange in the bentonite. However, the anions were mostly removed by electromigration, resulting in the reduction of the soil electrical conductivity. The field study demonstrated that in situ EK process is feasible for the remediation of greenhouse soils. In addition, the improvement of EK system and the role of bentonite backfill were discussed.

Laboratory Assessment of Kaolinite and Bentonite under Chemicalelectrokinetic Treatment

Electrokinetic treatment uses low intensity direct electric current or a low electric potential difference, to improve the engineering properties of subsurface soils while having minimum disturbance to the surface. This study aims to investigate the effects of chemical-electrokinetic treatment on properties of two types of clay soils at different intervals under the coupled Chemical, Hydraulic and Electrical (CHE) gradient. “Chemical-electrokinetic treatment” refers to improvement of soil with electrokinetic together with addition of chemical enhancement solution. The enhancement solutions used in this study are hydrated lime and saline solution. The combined effects of these processes together with various electrochemical and geochemical reactions would change the chemical composition of the soil porous medium, hence modifies the properties of the soil. The experiments were conducted in the laboratory using stainless steel electrodes under total applied voltage of 30 V for period of 15 days. Two types of fine-grained soils, kaolinite and bentonite, were used as they possess different mineralogy and geotechnical properties. The cumulative electro-osmotic flow and electric current flow through the soil samples were measured for period of 15 treatment days. Subsequently the specimens were tested for moisture content, pH and Atterberg Limit variations and the results have been reported. Test results revealed that there is a potential of developing this technique to improve engineering properties of finegrained soils, in particular to stabilise and improve soft soils for infrastructure management and constructions.

Remediation of contaminated marine sediment using electrokinetic–Fenton technology

In this work dredge marine sediments contaminated by petroleum hydrocarbon (TPH) and metals, such as Zn, Pb, Cu and Hg, were treated by electrokinetic treatment. EDTA and Tween 80 were used as processing fluid to enhance the solubility of metals and TPH, respectively. On the other hand, a combination of a Fenton's reagent and EDTA was evaluated to promote the in situ degradation of TPH and to solubilize the metals. After 30 days of treatment, the best results were obtained by EK–Fenton–EDTA process with a removal of about 90% for TPH, 57.3% of Zn, 59.8% of Pb, 59.4% of Cu and 54.5% of Hg.

염류집적 농경지의 전기동력학적 정화

The influence of operation time on electrokinetic restoration was investigated to remove salts from sulfate-accumulated greenhouse soil. Operation time is directly related to the process cost, therefore, we determined the relationship between operation time and removal of salts. Nitrate and sodium were removed almost completely within 2 weeks, chloride and calcium was removed in proportion to the operation time. Sulfate was accumulated at the center of anode and cathode. The soil electrical conductivity (EC), an indicator for soil salinity, showed similar shape with the residual sulfate after electrokinetic treatment. The soil EC was not changed after 2 weeks, however, the energy consumption increased with operation time. Based on the experimental results, most salts except sulfate were removed within 2 weeks, but sulfate was not removed during same time period. For the further removal of sulfate, longer operation time is in need.