Electrodialytic Remediation Research Articles

Electrodialytic Remediation of Soil Slurry–Removal of Cu, Cr, and As

Severe soil contamination is often found at old wood preservation sites and a common combination of pollutants is Cu, Cr, and As. In the present work it is tested if simultaneous removal of Cu, Cr, and As can be obtained in an electrodialytic cell where the polluted soil is remediated as a stirred suspension (placed as the desalination compartment in accordance to the position of the ion exchange membranes). The soil for the experiments was sampled at an abandoned wood preservation site and contained 2170 mg Cu/kg, 710 mg Cr/kg and 3200 mg As/kg. SEM-EDX analysis showed that Cu, Cr, As and oxygen formed particles that were cementing soil minerals together. The soil was suspended in distilled water, distilled water with I2 crystals to have an oxidizing environment, or in an acidified environment at pH about 1.0. The experiments lasted from 1 to 3 weeks. Good results were obtained in two experiments; an experiment where the soil was suspended in distilled water and the remediation lasted 3 weeks with 2.5 mA and an experiment with acidification of the soil suspension with HNO3 to pH about 1.0 (2 weeks and 5 mA). The best separation of pollutants and soil was obtained in the experiment with suspension in distilled water. Based on soil concentrations, good Cu removal (95%) was obtained in both experiments. Removal of Cr was most efficient from the acidified soil suspension (74%). Both Cu and Cr concentrations were below the limiting values after the remediation. The As concentration, however, was not even although 61% was removed. In the soil remained about 1070 mg As/kg soil and since the limiting value is 40 mg As/kg, the removal was not efficient enough. So simultaneous removal was possible, but the target values were only met in the case of Cu and Cr, and more research is needed to remove As to a sufficiently low concentration, as well.

Electrodialytic remediation of harbour sediment in suspension—Evaluation of effects induced by changes in stirring velocity and current density on heavy metal removal and pH

Electrodialytic remediation was used to remove heavy metals from a suspension of dredged harbour sediment. The studied metals Cu, Pb, Zn and Cd are normally strongly bound in anoxic sediment. Six electrodialytic laboratory remediation experiments were made, lasting 14 days and under oxic conditions. The influence on the metal removal was investigated by changing current densities and stirring velocity of the sediment suspension. Using a current density of 1.0 mA/cm 2 gave the highest metal removal. The sediment suspension was partly oxidised when mixed into a suspension for the electrodialytic remediation experiments and was further oxidised during the experiments. Even at low stirring velocities, oxic conditions were obtained. The metal removal was dependent on the achieved pH in the sediment and the highest metal removal and corresponding low pH was obtained by using a current density of 1.0 mA/cm 2 and a stirring velocity of the sediment suspension of 1000 rpm. The highest removal obtained was 98% Cd, 78% Zn, 65% Pb and 44% Cu after 14 days of remediation. The metal removal was more dependent on the stirring velocity than on the current density. When manually stirring the sediment suspension or using a stirring velocity of 60 rpm the sediment deposited, which led to a slightly higher pH in the sediment and keeping all the sediment in suspension is essential for a successful remediation.

Electrodialytic remediation of copper mine tailings using bipolar electrodes

In this work an electrodialytic remediation (EDR) cell for copper mine tailings with bipolar stainless steel plates was analyzed. The bipolar plates were inserted inside the tailings, dividing it into independent electrochemical cells or sections, in order to increase the copper removal efficiency from mine tailings. The bipolar plates design was tested on acidic copper mine tailings with a fixed: applied electric field, liquid content, initial pH, and remediation time. The laboratory results showed that inserting bipolar plates in EDR cells improves the remediation action, even though the applied electric field is reduced by the electrochemical reactions on the plates. Basically three aspects favor the process: reduction of the ionic migration pathways, increase of the electrode surface, and in-situ generation of protons (H +) and hydroxyls (OH −). Furthermore, the laboratory results with citric acid addition significantly improve the remediation actions, reaching copper removal of up to nine times better, compared to conventional EDR experiments without any plates or citric acid addition.

Preliminary treatment of MSW fly ash as a way of improving electrodialytic remediation

In the current work electrodialytic remediation (EDR) was applied to remove heavy metals from municipal solid waste (MSW) fly ash, a hazardous waste collected during flue gas treatment. Tests were conducted to evaluate if EDR could be improved by introducing a preliminary treatment in which very soluble salts were removed. Three different preliminary treatments were conducted with different L:S ratios and pH. Treatment in which metal release and L/S ratio were lower was selected for EDR. Electrodialytic remediation was performed at a constant current of 38 mA, for 14 days, using gluconate as a solubilisation enhancement agent. Conductivity and pH were monitored and electrolyte samples were collected every 4 days to evaluate metal release over time. It was found that the preliminary treatment reduces fouling of the ion-exchange membranes used in EDR and drastically increases the removal of metals. Remediation time was also considerably reduced. Additionally, preliminary washing reduces energy consumption during EDR, since electric current is not wasted in the transport of soluble salts. Sequential extraction was performed in the untreated and treated samples to help identify how metals are bond to the fly ash. It was seen that at the end metals are mainly found in the strongly bonded and residual phases. This indicates that the combined treatment (washing + EDR) is successful in reducing the environmental risk posed by fly ash.

Electrodialytic remediation of suspended mine tailings

This work shows the laboratory results of nine electrodialytic remediation experiments on copper mine tailings. A newly designed remediation cell, where the solids were kept in suspension by airflow, was tested. The results show that electric current could remove copper from suspended tailings applying 40 mA during 7 days. The liquid-to-solid ratios used were 3, 6 and 9 mL g− 1. With addition of sulfuric acid, the process was enhanced because the pH decreased to either 2 or 4, and copper was therefore dissolved. The maximum copper removal was 80% with addition of sulfuric acid in 7-day experiment at 40 mA, with approximately 137.5 g mine tailings on dry basis. The removal for a static (baseline) experiment only amounted 15% when passing approximately the same amount of charge through 130 g of mine tailings. The use of air bubbling to keep the tailings suspended increased the removal efficiency from 1% to 80% compared to experiments with no stirring but with the same operational conditions. This showed the crucial importance of having the solids in suspension and not settled during the remediation.

Changes in chromium distribution during the electrodialytic remediation of a Cr (VI)-contaminated soil

A laboratory study has been carried out to determine the feasibility of in situ remediation of chromium (VI)-contaminated soil using electrodialysis in relation to its speciation in soil. This technique is best suited for low-permeability soils or sediments, which may be difficult to remediate by other means and implies the application of a low-intensity direct current to the soil, which is separated from the electrode compartments by ion-exchange membranes. A clayey soil was prepared for use in the experiments and was characterized before being mixed with a solution of potassium dichromate for several days to produce a final Cr content of 4,056 mg/kg of soil dry wt. Remediation tests were carried out under constant-voltage conditions for periods of 7-14 days and the evolution of applied current to the cell, pH, and conductivity of the electrolytes were recorded periodically. Fractionation of chromium was determined for soil samples before and after remediation using a standardized four-step sequential extraction procedure (SEP) with acetic acid, hydroxylamine, hydrogen peroxide, and aqua regia solutions. Results show that chromium is mobilized from the most labile phases (soluble/exchangeable/carbonate). In a 15 V test, SEP results show that the amount of chromium extracted in the first step drops from 80% to 9%, but also that changes in the total chromium distribution occur during the treatment with some transferred to other soil phases that are more difficult to mobilize.

Organic acid enhanced electrodialytic extraction of lead from contaminated soil fines in suspension

AbstractThe implementation of soil washing technology for the treatment of heavy metal contaminated soils is limited by the toxicity and unwieldiness of the remaining heavy metal contaminated sludge. In this work, the feasibility of combining electrodialytic remediation with heterotrophic leaching for decontamination of the sludge was investigated. The ability of 11 organic acids to extract Pb from the fine fraction of contaminated soil (grains < 63 µm) was investigated, and application of the acids as enhancing reagents during electrodialytic remediation (EDR) of Pb‐contaminated soil fines in suspension was tested. Five of the acids showed the ability to extract Pb from the soil fines in excess of the effect caused solely by pH changes. Addition of the acids, however, severely impeded EDR, hence promotion of EDR by combination with heterotrophic leaching was rejected. In contrast, enhancement of EDR with nitric acid gave promising results. Copyright © 2007 Society of Chemical Industry

Leaching Properties of Estuarine Harbor Sediment before and after Electrodialytic Remediation

Electrodialytic remediation (EDR) can be used to extract heavy metals from a variety of different media. In this work, contaminated harbor sediments from two locations in the United States and one in Norway were subjected to EDR, and were compared with batch extractions conducted with the sediment. pH-dependent leaching tests were used to evaluate changes in leaching properties of treated and control sediments. Significant fractions of total concentrations were removed during treatment (35–95% with an average of 75% for all sediments and elements investigated). The release of elements in pH-dependent leaching tests, however, demonstrated equal or greater leaching from treated sediments in the neutral pH range. Dissolved organic carbon appears to be a significant contributor to post-treatment increases in leaching, and dissolution of significant iron and aluminum sorption sites is hypothesized to also play a role. This research highlights the importance of understanding contaminant speciation and availability, as total metals concentrations, in this particular case, do not relate to estimates of the environmental availability of metals (total concentrations were typically two to three orders of magnitude greater than concentrations released during pH-dependent leaching).

The Effect of Soil Type on the Electrodialytic Remediation of Lead-Contaminated Soil

This work investigates the influence of soil type on electrodialytic remediation (EDR) of lead (Pb). In electrokinetic soil remediation, it is well known that pH is a key factor and that carbonate ...

Electrodialytic remediation of soil fines (

Current treatment of the remaining soil fines from soil wash is onerous and expensive, and therefore, in this work, we investigated the feasibility of electrodialytic remediation (EDR) as an alternative treatment. The study focuses on EDR efficiency as a function of current strength, liquid-to-solid-ratio (L/S), pH and time. We found out that during the experiments, Pb was easily dissolved by the acidification resulting from water splitting at the anion-exchange membrane. When higher currents and/or higher L/S ratios were applied, it was found that water splitting occurring at the cation-exchange membrane increased the pH, and this resulted in decreased remediation efficiency. It was shown that complete remediation of the soil-fines is possible, with the majority of the Pb being transported into the catholyte and precipitated at the cathode. Based on the results it is recommended that EDR is implemented using a number of reactors in series, where the initial reactor works at the highest possible removal rate, and the final reactor works at the target Pb-concentration.

Modeling of electrodialytic and dialytic removal of Cr, Cu and As from CCA-treated wood chips

A one-dimensional model is developed for simulating the electrodialytic and dialytic treatment of a saturated bed of wood chips containing chromium, copper and arsenic. The movement of Cr, Cu and As is mathematically modeled taking into account the diffusion transport resulting from the concentration gradients of their compounds and the electromigration of their ionic, simple and complex species during the operation. The model also includes the electromigration of the non-contaminant principal ionic species in the system, H + and OH −, proceeding from the electrolysis at the electrodes, Na + and NO 3 - used as electrolyte solutions in the electrode compartments, and oxalate ions and protons incorporated with the oxalic acid solution during wood chips incubation. The model simulation also takes into account that OH − generated on the cathode, during electrodialytic remediation, is periodically neutralized by addition of nitric acid in the cathode compartment. The anion and cation-exchange membranes are simply represented as ionic filters that preclude the transport of co-ions (the cations and anions respectively) with the exception of H +, which is retarded but considered to pass through the anion-exchange membrane.

Kinetics of electrodialytic extraction of Pb and soil cations from a slurry of contaminated soil fines

The objective of this work was to investigate the kinetics of Pb-removal from soil fines during electrodialytic remediation in suspension, and study the simultaneous dissolution of common soil cations (Al, Ca, Fe, Mg, Mn, Na and K). This was done to evaluate the possibilities within control of the remediation process to leave a final product suitable for reuse. The Pb-remediation process could be divided into four phases: (1) a “lag-phase”, (2) a period with a high removal rate (7.4 mg/day in average at 40 mA), (3) a period with a low removal rate, and (4) a period where no further Pb-removal was obtained. During the first phase, dissolution of carbonates was the prevailing process, resulting in a corresponding loss of soil mass. During this phase, the investigated ions accounted for the major current transfer, while, as remediation proceeded, hydrogen ions increasingly dominated the transfer. During phase (3) the high conductivity and low voltage suggested that removal may be accelerated by increasing the current density. Overall, 97% of the Pb could be extracted, reducing the final Pb-concentration to 25 mg/kg. The order of removal rates was: Ca > Pb > Mn > Mg > K > (Al and Fe).

Comparison of electrodialytic removal of Cu from spiked kaolinite, spiked soil and industrially polluted soil

Electrokinetic remediation methods for removal of heavy metals from polluted soils have been subjected for quite intense research during the past years since these methods are well suitable for fine-grained soils where other remediation methods fail. Electrodialytic remediation is an electrokinetic remediation method which is based on applying an electric dc field and the use of ion exchange membranes that ensures the main transport of heavy metals to be out of the pollutes soil. An experimental investigation was made with electrodialytic removal of Cu from spiked kaolinite, spiked soil and industrially polluted soil under the same operational conditions (constant current density 0.2mA/cm2 and duration 28 days). The results of the present paper show that caution must be taken when generalising results obtained in spiked kaolinite to remediation of industrially polluted soils, as it was shown that the removal rate was higher in kaolinite than in both spiked soil and industrial polluted soil. The duration of spiking was found to be an important factor too, when attempting to relate remediation of spiked soil or kaolinite to remediation of industrially polluted soils. Spiking for 2 days was too short. However, spiking for 30 days resulted in a pattern that was more similar to that of industrially polluted soils with similar compositions both regarding sequential extraction and electrodialytic remediation result, though the remediation still progressed slightly faster in the spiked soil. Generalisation of remediation results to a variety of soil types must on the other hand be done with caution since the remediation results of different industrially polluted soils were very different. In one soil a total of 76% Cu was removed and in another soil no Cu was removed only redistributed within the soil. The factor with the highest influence on removal success was soil pH, which must be low in order to mobilize Cu, and thus the buffering capacity against acidification was the key soil characteristics determining the Cu removal rate.

Electrodialytic remediation of CCA-treated waste wood in a 2 m 3 pilot plant

Waste wood that has been treated with chromated-copper-arsenate (CCA) poses a potential environmental problem due to the content of copper, chromium and arsenic. A pilot plant for electrodialytic remediation of up to 2 m 3 wood has been designed and tested and the results are presented here. Several process parameters were investigated, and it was found that the use of collecting units and soaking of the wood prior to the electrodialytic process had a positive influence on the remediation process. There was a tendency towards higher removal of CCA from wood chips < 2 cm, compared to larger wood size fractions. The best remediation efficiency was obtained in an experiment with an electrode distance of 60 cm, and 100 kg wood chips. In this experiment 87% copper, 81% chromium and > 95% arsenic were removed. One other experiment was also analysed for arsenic. In this experiment the distance between the working electrodes was 1.5 m and here 95% As was removed. The results showed that arsenic may be the easiest removable of the copper, chromium and arsenic investigated here. This is very encouraging since arsenic is the CCA components of most environmental concern.

Electrodialytic remediation of copper mine tailings: Comparing different operational conditions

This work compares and evaluates sixteen electrodialytic laboratory remediation experiments on copper mine tailings. Different parameters were analyzed, such as remediation time, voltage drop, addition of desorbing agents, and the use of pulsed electrical fields. The results show that electric current could remove copper from watery tailings slowly. With addition of sulphuric acid, the process was improved due to a pH decrease from 6.7 to around 4, and the copper by this reason was released in the solution. Moreover, with citric acid addition the process was further improved due to a formation of copper citrate complexes. Using pulsed electric fields the remediation process with sulphuric acid addition was also improved by a decrease in the polarization cell. Main results: considering remediation with watery tailing as the base line, for three weeks experiments no copper removal was observed, adding sulphuric acid total copper removal reached 39%. Adding citric acid, total copper removal was improved in terms of remediation time: after 5 h experiment copper removal was 16% instead of 9% obtained after 72 h with sulphuric acid addition. Using pulsed electric fields total copper removal was also improved: for 72 h experiment the total copper removal was doubled (from 9% to 19%) compared to DC electric fields.

Acidification of Harbor Sediment and Removal of Heavy Metals Induced by Water Splitting in Electrodialytic Remediation

Harbor sediments are often contaminated with heavy metals, which can be removed by electrodialytic remediation. Water splitting at the anion exchange membrane in contact with the contaminated material in electrodialytic remediation is highly important for the removal of heavy metals. Here it was investigated how acidification caused by water splitting at the anion exchange membrane during electrodialytic remediation of contaminated harbor sediment and hence the metal removal, was influenced by different experimental conditions. Two different experimental cells were tested, where the number of compartments and ion exchange membranes differed. Totally, 14 electrodialytic experiments were made, with varying remediation time, current densities, and liquid to solid ratio (L/S). pH in the sediment decreased slightly after 1 day of remediation, even if the sediment had a high buffering capacity, suggesting that water splitting at the anion exchange membrane started early in the remediation process. An increase in the voltage over the cell and a decrease in the electrical conductivity in the sediment suspension also indicated that the water splitting started within 1 day of remediation. When the sediment was acidified, the voltage decreased and electrical conductivity increased. After 5 days of remediation the sediment was acidified at the chosen current density (1 mA/cm2) and the main metal removal was observed shortly after. Thus it was crucial for the metal removal that the sediment was fully acidified. Lower metal removal was seen in an experimental cell with three compartments compared to five compartments, due to increased sensitivity of pH changes in the cell.

Electrodialytic Remediation of Copper Mine Tailings: Sulphuric and Citric Acid Addition

Decades of mining activities in Chile have generated large amounts of solid waste, which have been deposited in mine tailing impoundments. These impoundments cause concern due to dam failures or natural leaching to groundwater and rivers. This work shows the laboratory results of 11 electrodialytic remediation experiments on copper mine tailings with the addition of sulphuric and citric acid. Comparing this to electrodialytic remediation with watery tailing, both acids enhanced the process. However, with citric acid addition the process was further enhanced because besides the pH decrease a formation of copper citrate complexes occurred. The maximum copper removal reached in the anode side of the remediation cell was 53% with sulphuric acid in 504 h and 35% with citric acid in only 40 h, both experiments at 20 V treating approximately 1.7 kg mine tailing on dry basis.

Effect of Major Constituents of MSW Fly Ash During Electrodialytic Remediation of Heavy Metals

Electrodialytic remediation (EDR) is a technique in which contaminants are removed from waste material by applying an electric field which forces their movement into concentration chambers through ion‐exchange membranes. In the current work EDR is used for the treatment of heavy metal–contaminated fly ash. The objective is to study the impact of major constituents of fly ash on remediation times, on efficiency, and on the performance of membranes. The results show that major constituents foul the ion‐exchange membranes, decreasing their ability to transport metal ions out of the waste compartment.

The use of desorbing agents in electrodialytic remediation of harbour sediment

Electrodialytic removal of Cu, Zn, Pb and Cd from contaminated harbour sediment was made with the emphasis of testing the effectiveness of different desorbing agents: HCl, NaCl, citric acid, lactic acid, ammonium citrate and distilled water. Extraction experiments with the desorbing agents were made prior to the electrodialytic experiments. The extractions showed that HCl was most efficient for metal desorption, probably due to the low pH and complexation with chloride. The metals were not extracted by distilled water. However, in the electrodialytic experiments, the removal was high when using distilled water and the desorbing agents did generally not enhance the heavy metal removal compared to distilled water. The only exception was with lactic acid, where the Cu removal was 20% higher compared to the other desorbing agents. The removal was 48% Cu, 80% Zn, 96% Pb and 98% Cd, when using distilled water. Metal speciation with the different desorbing agents was simulated with the geochemical model Visual MINTEQ version 2.15. Variations in the Cl concentration were found to be of crucial importance since it influences the formation of metal chlorocomplexes, especially uncharged species. All the acidic desorbing agents were predicted to form mostly cationic species, which was in agreement with the removal direction in the electrodialytic remediation experiments.

Electrodialytic removal of heavy metals from municipal solid waste incineration fly ash using ammonium citrate as assisting agent

Electrodialytic remediation, an electrochemically assisted separation method, has previously shown potential for removal of heavy metals from municipal solid waste incineration (MSWI) fly ashes. In this work electrodialytic remediation of MSWI fly ash using ammonium citrate as assisting agent was studied, and the results were compared with traditional batch extraction experiments. The application of electric current was found to increase the heavy metal release significantly compared to batch extraction experiments at comparable conditions (same liquid-to-solid ratio, same assisting agent, and same extraction time). Up to 86% Cd, 20% Pb, 62% Zn, 81% Cu and 44% Cr was removed from 75 g of MSWI fly ash in electrodialytic remediation experiments using ammonium citrate as assisting agent. The time range for the experiments varied between 5 and 70 days.