Electrokinetic Remediation Process Research Articles

Electrokinetic remediation of arsenate spiked soil assisted by CNT-Co barrier—The effect of barrier position and processing fluid

An enhanced electrokinetic (EK) remediation process coupled with permeable reaction barrier (PRB) of carbon nanotube coated with cobalt (CNT-Co) has been investigated for As(V) removal from soil under potential gradient of 2.0 V/cm for 5 days treatment. Results showed that removal efficiency of As(V) was greater than 70% in EK/CNT-Co system with EDTA as processing fluid, which was enhanced by a factor of 2.2 compared to EK system and EK/CNT systems. A better removal performance in EK/CNT-Co system was attributed to higher sorption of As(V) onto CNT-Co than onto CNT. Removal of As(V) in EK/CNT-Co system was mainly contributed by surface sorption on CNT-Co rather than by EK process. The surface characteristics of CNT-Co, which was qualified by SEM coupled with EDS, were clearly confirmed that arsenic was adsorbed on the passive layer surface. Among EK processes, As(V) removal was dominated by electroosmosis flow and electromigration in EK/CNT-Co system with groundwater and EDTA as processing fluid. An investigation with sequential extraction revealed that As(V) associated with soils was considerably shifted from strong binding forms, i.e., Fe-Mn oxide, organic, and residual, to weak binding forms, i.e., exchange and carbonate, after EK/CNT-Co treatment.

Remediation of phenanthrene from contaminated kaolinite by electroremediation-Fenton technology

Polycyclic aromatic hydrocarbons (PAHs) cause a high environmental impact when released into the environment. The objective of this study was to evaluate the capacity to decontaminate polluted soils with phenanthrene as a model PAH using a combination of two technologies: electrokinetic remediation and Fenton process. Kaolinite was used as a model sample that was artificially polluted at the laboratory at an initial concentration of phenanthrene of 500 mg kg−1 of dried kaolinite. The standard electrokinetic process resulted in negligible removal of phenanthrene from the kaolinite sample. Faster and more efficient degradation of this compound can be promoted by introduction of a strong oxidant into the soil such as hydroxyl radicals. For this reason, the Fenton reactions have been induced in several experiments in which H2O2 (10%) was used as flushing solution, and kaolinite polluted with iron was used. When anode and cathode chambers were filled with H2O2 (10%), the kaolinite pH is maintained at an acid value around 3.5 without pH control and an overall removal and destruction efficiency of phenanthrene of 99% was obtained in 14 days by applying a voltage gradient of 3 V cm−1. Therefore, it is evident that a combined technology of electrokinetic remediation and Fenton reaction is capable of simultaneously removing and degrading of PAHs in polluted model samples with kaolinite.

Enhancement of electrokinetic remediation of arsenic spiked soil by chemical reagents

An enhanced electrokinetic remediation process for removal of arsenic, presented as As(V) form, from spiked soil has been investigated with groundwater (GW) and chemical reagents of cetylpyridinium chloride (CPC, a cationic surfactant), ethylenediaminetetraacetic acid (EDTA) and citric acid (CA) under potential gradient of 2.0–3.3 V/cm for 5 days treatment. The removal efficiency of As(V) in EK-EDTA system was better than that in other two EK systems. As potential gradient increased from 2.0 V/cm to 3.0 V/cm, the removal efficiency of As(V) was increased from 35.4% to 44.8% in EK-EDTA system. It showed that the arsenic removal could be enhanced by selecting suitable chemical reagent and increasing potential gradient. The intensive of electroosmotic flow towards the cathode caused a significant retardation of electromigration of arsenic towards the anode. The quantity of As(V) collected in anode reservoir was 1.4–2.5 times greater than that in cathode reservoir for all EK systems. It implied that As(V) removal was directly related to the electromigration rather than electroosmosis mechanism in EK systems. A further investigation need to be conducted to achieve higher removal efficiency of As(V).

Concentration of copper and a copper–EDTA complex at the pH junction formed in soil by an electrokinetic remediation process

The formation and stability of a pH junction was investigated, and the precipitation and accumulation of a metal hydroxide at the pH junction was confirmed. Moreover, the possibility that metal ions could be accumulated as a Me–EDTA complex at the pH junction was demonstrated. As a result, the pH junction where the acidic and alkali fronts of soil meet and the pH of soil changes rapidly, appeared at the 0.6 position in the EK process for 6–12 h. Copper ions accumulated in the form of copper hydroxide. EDTA was also concentrated in the position, in general agreement with the position of the pH junction. In addition to copper hydroxide, a copper–EDTA complex was concentrated at the 0.6 position from the anode after EK treatment for 12 h. The copper–EDTA complex was retained in 0.7 position from the anode after 12 h and, after 24 h, the position shifted to 0.8–0.9 from the anode. The possibility of accumulating metal ions within a narrow area, such as a pH junction was demonstrated.

Electrokinetic remediation of copper mine tailings: Implementing bipolar electrodes

Important process parameters to optimize in electrokinetic soil remediation are those influencing remediation time and power consumption since these directly affect the cost of a remediation action. This work shows how the electrokinetic remediation (EKR) process could be improved by implementing bipolar electrodes in the porous material. The bipolar electrodes in EKR meant two improvements: (1) a shorter migration pathway for the contaminant, and (2) an increased electrical conductivity in the remediation system. All together the remediation proceeded faster with lower electrical resistance than in similar experiments but without the bipolar electrodes. The new electrokinetic remediation design was tested on copper mine tailings with different applied electric fields, remediation times and pre-treatment. The results showed that the copper removal was increased from 8% (applying 20 V for 8 days in sulphuric acidified tailings) without bipolar electrodes to 42% when bipolar electrodes were implemented. Furthermore, the results showed that in this system sulphuric acid addition prior to remediation was better than citric acid addition. In addition, applying a too strong electric field (even with bipolar electrodes) could cause a severe polarization (e.g. a high electrical resistance) in the remediation system.

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 0.01 M 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.

Electrokinetically Enhanced Settlement and Remediation of Contaminated Sediment

Abstract Electrokinetic technique has been used in sedimentation at mining applications as a volume reduction for slurry tailing wastes. This technique has been used in remediation for environmental application as a potential in-situ remediation method for contaminated soils and wastes. Thus electrokinetic technique can be used in sedimentation and remediation of sediments. A regulated constant voltage was applied on the testing sample, directed upward, top cathode (−) and bottom anode (+) during electrokinetic sedimentation process. On the other hand, constant voltage was applied on the testing sample, directed downward, top anode (+) and bottom cathode (−) during electrokinetic remediation process. This means that the polarity reversal was employed. The time dependent settlement and concentration due to electrophoresis and electro-osmosis was measured on an hourly basis. The sedimentation rate of specimen and removal rate of contaminant in contaminated sediment were increased with increasing of applied voltages.

Dewatering and decontamination of artificially contaminated sediments during electrokinetic sedimentation and remediation processes

Sediments contain significant water, clay, colloidal fraction and contaminants, and can result in soft strata with high initial void. Its potential hazards of the sediments are existed in subsurface environments. Electrokinetic technique has been used in sedimentat ion and remediation for volume reduction of slurry tailing wastes and extraction of contaminants from contaminated soils. In this research, the coupled effects of sedimentation and remediation of contaminated sediments are investigated using electrokinetic sedimentation and remediation techniques from experimental aspects. A series of laboratory experiments including variable conditions such as initial solid content of the specimen, concentration level of the contaminant, and magnitude of applied voltage are performed with the contaminated sediment specimens mixed with ethylene glycol. Commercially available high specification Kaolin was used to simulate sediment. From the test results, the quantity of accumulated outflow is increased with increasing voltage applied, otherwise the quantity of accumulated outflow is decreased with increasing solid content and contamination level. The removal speed and time of contaminant was shortened with increasing voltage applied, and with decreasing solid content and contamination level.

Surface Speciation Modeling of Heavy Metals in Kaolin: Implications for Electrokinetic Soil Remediation Processes

The driving mechanisms for flux occur at interface between the soil particles and solution during electrokinetic soil remediation and the nature of this interface affects the electrokinetic response of the system. The pH-dependent adsorption of heavy metal contaminants by kaolin and the sensitivity of kaolin zeta potential to the aqueous phase properties are two important aspects that complicate the metal movement during electrokinteic soil remediation. This paper addresses these aspects and presents an electrostatic adsorption model that describes the behavior of kaolin surface for Cr(VI), Cr(III), Ni(II), and Cd(II) under various chemical conditions. This study showed that the aqueous properties: pH, ionic strength and the presence of the heavy metals Cr(VI), Cr(III), Ni(II), and Cd(II) in the system affect the zeta potential of kaolin surface. The zeta potential of kaolin shifts to a more negative value if the system pH increases. However, it shifts to a more positive value if the system ionic strength or metal concentration increases. It was found that the amount of the heavy metal adsorbed by kaolin has a pronounced sensitivity to the pH. As a result of the adsorption modeling, the constant capacitance protonation-dissociation intrinsic constants of kaolin are: pK int =− 3.8 ± 0.5 and pK int − = 9.4 ± 0.5. The ion-kaolin surface complexation constants (pK int )o fCr(VI), Cr(III), Ni(II), and Cd(II) are: −12.5 ± 0.5, −5.0 ± 1.0, 2.6 ± 0.6, and 3.3 ± 1.0, respectively.

In Situ Speciation Studies of Copper–Humic Substances in a Contaminated Soil during Electrokinetic Remediation

Speciation of copper-humic substances (HS) in the electrokinetic remediation (EKR) of a contaminated soil was studied by in situ extended X-ray absorption fine structure (EXAFS) and X-ray absorption near edge structure (XANES) spectroscopies. The least-square fits of the XANES spectra suggested that the main Cu species in the contaminated soil were Cu-HS (50%), CuCO(3) (28%), Cu(2)O (11%), and CuO (11%). The Cu-HS in the contaminated soil possessed equatorial and axial Cu-O bond distances of 1.94 and 2.17 A with coordination numbers (CNs) of 3.6 and 1.4, respectively. In the EKR process, the axial Cu-O bond distance in the Cu-HS complexes was increased by 0.15 A, which might be due to a ligand exchange of the Cu-HS with H(2)O molecules in the electrolyte. After 180 min of EKR, about 50% of the Cu-HS complexes (or 24% of total Cu) in the soil were dissolved and formed [Cu(H(2)O)(6)](2+) in the electrolyte, 71% (or 17% of total Cu in the soil) of which were migrated to the cathode under the electric field (5 V/cm). This work exemplifies the use of in situ EXAFS and XANES spectroscopies for speciation studies of Cu chelated with HS in the contaminated soil during EKR.

Effects of Electric Current and Potential on the Electrokinetic Removal of Heavy Metals from an Abandoned Mine Tailings

In the removal of heavy metals from the mine deposit using electrokinetic processes, the effects of operation under both constant current and constant potential conditions were estimated. The results of soil pH distributions for DDW-20 V and DDW-100 mA cases after the electrokinetic remediation tests were observed. In the former case, soil pH was not much changed and kept to almost constant value just little higher than initial soil pH of 3.52, except near the cathode, which was about pH 5. While in the latter case, soil pHs of anode and the cathode regions were less than pH 3 and about 6, respectively. The electroosmotic flow to the cathode increased rapidly till 10 hrs and decreased steadily and then maintained to constant rate until the end of operation at constant current condition. Electric potential gradient was continuously increased to as much as 34.375 V/cm. At the steady state, values of the apparent electric conductivity for DDW-20 V and DDW-100 mA were around 40 <TEX>${\mu}\textrm{s}$</TEX>/cm and 30 <TEX>${\mu}\textrm{s}$</TEX>/cm, respectively. In the DDW-100mA test, Cu, Cd, and Zn except Pb showed the tendency of moving toward the cathode. While in the DDW-20 V case, it was observed that Cu, Zn, and Pb except Cd were not moved to any directions. The results of the tests demonstrated that the electrokinetic soil remediation process could be operated better under constant current condition than constant electric potential condition.

Hemi-hydrogenation of dinitriles

Over the last century, electrochemical engineering has contributed significantly to societal progress by enabling development of industrial processes for manufacturing chemicals, such as chlorine and the Nylon precursor adiponitrile, as well as a wide range of metals including aluminium and zinc. In 2011, ca. 17 M tonne Cu p.a. was electro-refined to 99.99%+ purity required by electrical and electronic engineering applications, such as for electrodepositing with exquisite resolution multi-layer inter-connections in microprocessors. Surface engineering is widely practised industrially e.g. to protect steels against corrosion e.g. by electroplating nickel or using more recent novel self-healing coatings. Complex shapes of hard alloys that are difficult to machine can be fabricated by selective dissolution in electrochemical machining processes. Electric fields can be used to drive desalination of brackish water for urban supplies and irrigation by electrodialysis with ion-permeable membranes; such fields can also be used in electrokinetic soil remediation processes. Rising concerns about the consequences of CO2 emissions has led to the rapidly increasing development and deployment of renewable energy systems, the intermittency of which can be mitigated by energy storage in e.g. redox flow batteries for stationary storage and novel lithium batteries with increased specific energies for powering electric vehicles, or when economically viable, in electrolyser-fuel cells. The interface between electrochemical technology and biotechnology is also developing rapidly, with applications such as microbial fuel cells.Some of these applications are reviewed, the challenges assessed and current trends elucidated in the very active area of Chemical Engineering bordering with material science and electrochemistry.

Electrokinetic Processing for the Removal of Radionuclides in Soils

Electrokinetic soil remediation is one of the most promising soil decontamination processes because it has high removal efficiency and time effectiveness in low permeability soils, such as clay. Uranium and strontium were efficiently removed from kaolinite by electrokinetic remediation. In the case of cesium, the rate of removal may be significantly slower than those of the uranium and strontium. Acetic acid was effective as enhancement agent for buffering hydroxide ions produced by the cathode reaction, resulting in the prevention of the precipitation of uranium ions in the cathode region. This also decreased energy consumption because hydroxide precipitation increased the resistance and the electrical gradient across the soil cell. The use of citric acid was not efficient in removing uranium from kaolinite because the direction of electromigration was opposite to that of electroosmosis. Since most metal–citrate chelates are negatively charged, they were transported towards the anode by electromigration, whereas electroosmosis flowed toward the cathode, resulting in lowering removal efficiency. Uranium was not effectively removed from the weathered soil of black shale by electrokinetic remediation process. This may be due to the low proportion of the mobile ions because most of uranium exists in the residual fraction.

In-situ EXAFS study of copper in the electrokinetic remediation process.

The speciation of copper in the early stage of the electrokinetic remediation (EKR) process has been studied by extended X-ray absorption fine structure (EXAFS) spectroscopy in the present work. By in-situ EXAFS, we found that copper in a contaminated soil possessed a Cu-O bond distance of 1.98 A with a coordination number (CN) of 5.8. In the second shell, the bond distance of Cu-(O)-Cu was 2.87 A with a CN of 6.4. However, possibly due to the fact that incompact copper atoms in the outer shells were distorted by EKR, the Cu-(O)-Cu (2nd shell) bond distance and the CN of copper in the contaminated soil decreased by 0.08 A and 5.4, respectively in the early stage of the EKR process. Interestingly, after prolonging the contact time to about 80 minutes, the 1st-shell copper atoms were also perturbed by EKR. This work is an example of usefulness of the in-situ EXAFS spectroscopy for detailed studies of the speciation of copper in the contaminated soil during EKR process.

A new method to control electrolytes pH by circulation system in electrokinetic soil remediation

To simultaneously avoid a decrease of electro-osmotic flow by hydrogen ions and to increase heavy metal precipitation due to hydroxide ions, simulated electrokinetic remediation was conducted in saturated kaolinite specimens loaded with lead(II) using an electrolyte circulation method to control electrolyte pH. At an electrolyte circulation rate of 1.1 ml/min, it was possible to increase the anolyte pH from 2 to 4 and decrease the catholyte pH from 12 to 8. Using electrolyte circulation, it was observed that the rate of decrease of clay pH due to the change of electrolyte pH was reduced. As a result, the operable period was extended and the removal efficiency for lead(II) was also increased. It was observed that most of the effluent lead(II) from the cathode compartment was electroplated onto the cathode and that residual effluent lead(II) did not precipitate onto, or adsorb to, the clay at the anode compartment during circulation. Therefore, there was no need to treat the electrolyte because there was virtually no effluent from the cathode compartment in the circulation system. It was also found that the electrolyte volume required to sustain the electrolytic reaction was sufficient for the whole electrokinetic remediation process.

Cyclodextrin-Enhanced Electrokinetic Removal of Phenanthrene from a Model Clay Soil

Removal of hydrophobic organic contaminants (HOCs) from saturated low-permeability subsurface environments using a solubility-enhanced electrokinetic remediation process is demonstrated for a model...

Removal and degradation of phenol in a saturated flow by in-situ electrokinetic remediation and Fenton-like process

In this laboratory study, a sandy loam soil saturated with phenol solution was treated by in-situ electrokinetics-Fenton process incorporated with a permeable reactive wall of scrap iron powder (SIP). The soil was contaminated and saturated with aqueous phenol solution of 90–115 mg/kg in concentration. It was then placed in a soil cell. The soil cell was assembled with an anode reservoir and a cathode reservoir at its ends. A bed of SIP (1.05–32.69 g) was inserted in the soil cell at a distance of 5 cm from the anode reservoir compartment. For the test runs, 0.3% H 2O 2 was used as the anode reservoir fluid, whereas de-ionized water was used as the cathode reservoir fluid. An electric gradient of 1 V/cm was applied to enhance the saturated flow in the soil cell for a period of 10 days. Experimental results have shown that the electroosmotic (EO) flow quantity decreased as the amount of SIP increased. This phenomenon was in good agreement with the results showing the value of EO permeability increased with a decreasing amount of SIP. Results also showed that throughout the test period the cumulative, consumed mass of H 2O 2 in the anode reservoir increased as the amount of SIP decreased. On the other hand, the cumulative, increased mass of phenol in the cathode reservoir was found to increase with a decreasing amount of SIP. Meanwhile, the residual phenol concentration in the soil cell was found to decrease with a decreasing amount of SIP. When 1.05 g scrap iron powder was used, an overall removal and destruction efficiency of phenol of 99.7% was obtained. Therefore, it is evident that an in-situ combined technology of electrokinetic remediation and Fenton-like process is capable of simultaneously removing and degrading the phenol in a saturated flow.

Electrokinetic remediation of heavy metal-contaminated soils under reducing environments

This paper describes the migration of hexavalent chromium, Cr(VI), nickel, Ni(II), and cadmium, Cd(II), in clayey soils that contain different reducing agents under an induced electric potential. Bench-scale electrokinetic experiments were conducted using two different clays, kaolin and glacial till, both with and without a reducing agent. The reducing agent used was either humic acid, ferrous iron, or sulfide, in a concentration of 1000 mg/kg. These soils were then spiked with Cr(VI), Ni(II), and Cd(II) in concentrations of 1000, 500 and 250 mg/kg, respectively, and tested under an induced electric potential of 1 VDC/cm for a duration of over 200 h. The reduction of chromium from Cr(VI) to Cr(III) occurred prior to electrokinetic treatment. The extent of this Cr(VI) reduction was found to be dependent on the type and amount of reducing agents present in the soil. The maximum reduction occurred in the presence of sulfides, while the minimum reduction occurred in the presence of humic acid. The concentration profiles in both soils following electrokinetic treatment showed that Cr(VI) migration was retarded significantly in the presence of sulfides due both to the reduction of Cr(VI) to Cr(III) as well as an increase in soil pH. This low migration of chromium is attributed to: (1) migration of Cr(VI) and the reduced Cr(III) fraction in opposite directions, (2) low Cr(III) migration due to adsorption and precipitation in high pH regions near the cathode in kaolin and throughout the glacial till, and (3) low Cr(VI) migration due to adsorption in low pH regions near the anode in both soils. Ni(II) and Cd(II) migrated towards the cathode in kaolin; however, the migration was significantly retarded in the presence of sulfides due to increased pH through most of the soil. Initial high pH conditions within the glacial till resulted in Ni(II) and Cd(II) precipitation, so the effects of reducing agenets were inconsequential. Overall, this study demonstrated that the reducing agents, particularly sulfides, in soils may affect redox chemistry and soil pH, ultimately affecting the electrokinetic remediation process.

Model experimental study on the migration behavior of heavy metals in electrokinetic remediation process for contaminated soil

Recently in Japan, like in other industrialized countries, treatment of contaminated soil or ground has become an important issue in redeveloping such areas as old factories, mining sites, and other polluted sites. In these cases, measures such as a construction of cut-off walls and disposal to controlled waste disposal sites have been so far taken. But, the treatment of contaminated soils has become more difficult nowadays. Therefore, remediation of contaminated soil by removal or extraction of contaminants is necessary and various methods have been developed and applied in many countries. Authors have tried to develop an electrokinetic remediation method for soil contaminated with heavy metals and some basic and pilot scale experiments have been carried out. In this paper, the results of a model experiment using an artificial soil contaminated with Cu or Ph or Cr are presented as follows. i) In the electrokinetic process, migration of water to the cathode by electroosmosis, migration of ions to the cathode or anode by electrophoresis and electrolysis of water occur spontaneously. ii) Upon DC loading, Cu and Pb migrate to the cathode and accumulate as oxides or hydroxides near the cathode but are not removed from contaminated soil. However, in the case of Cr contaminated soil, Cr in the form of Cr(VI) migrates to the anode and is removed from soil through the drainage water. iii) After DC loading for 2 weeks, the concentration of exchangeable cations and composition of soil changed drastically while the CEC and clay mineralogy did not change appreciably.

Effects of electric field directions on surfactant enhanced electrokinetic remediation of diesel‐contaminated sand column

The removal of diesel from a sandy soil column was conducted by surfactant enhanced electrokinetic remediation process to study the effects of the electric field direction on the diesel removal efficiency. Anionic surfactant SDS(sodium dodecyl sulfate) was fed to one of the electrode chambers driven by electrokinetics and/or a pump. When an electric current was applied while SDS was fed to anode chamber at a constant rate by pump, an effluent flowrate higher than the feeding rate was obtained at cathode side because the directions of electroosmosis and pumped convective flow were identical. Meanwhile, when SDS was fed to cathode chamber by pump in the presence of an electric current, a lowered effluent flowrate was obtained, where the directions of electroosmosis and pumped flow were opposite. In this case, however, the diesel removal rate and total recovered amount of diesel were substantially increased compared to the case that SDS was fed to anode side. Results implied in SDS transport through the soil column that the electrophoretic transport of SDS anion towards anode was dominant over the retardation of SDS transport by the electroosmosis flowing towards cathode. The diesel mobilization would be achieved by solubilization of diesel components into SDS micelles and thus by transporting of SDS‐diesel complexes together convectively and electrophoretically towards anode side.