Electrokinetic Decontamination Research Articles

Empirical Mathematical Analysis of Electrokinetic Decontamination of Soils Polluted With Heavy Metals

Empirical Mathematical Analysis of Electrokinetic Decontamination of Soils Polluted With Heavy Metals

Molecular dynamics study on the zeta potential and shear plane of montmorillonite in NaCl solutions

Zeta potential and the position of the shear plane are key physical properties characterizing the behavior of clay minerals in the colloidal system, and have been applied in many fields such as electroosmotic consolidation and electro-kinetic decontamination. In the past decades, numerous studies have been conducted on measuring and calculating the zeta potential. Nevertheless, few researchers have been reported to achieve a systematic understanding and predicting the zeta potential and the shear plane's position, especially for clay particles. This paper provided a molecular dynamics (MD)-based method to determine the zeta potential and shear layer thickness simultaneously to fill the gap. In the paper, the structure of the electrical double layer (EDL) was investigated for montmorillonite mesopore containing NaCl electrolyte in the concentration of 0.20–1.30 mol/L. The density profiles of ion species were well predicted by the Stern model, combining the Stern potential's determination. The calculated zeta potential based on the electroosmotic velocity profile in nonequilibrium molecular dynamics (NEMD) simulation was improved by introducing the slip length and was found to be closely comparable to the experimental values. Furthermore, the results confirmed that the shear plane cannot be observed from the electroosmotic velocity profile and self-diffusion coefficient of species in the MD simulation. The position of the zeta potential was determined by the Stern model and triple-layer model (TLM), showing a certain distance from the Stern plane. The zeta position was found that has a linear relationship with the Debye length and linearly depends on the ionic strength in the log scale, in agreement with previous investigations. The findings provided a systematic insight into the electrical double layer structure, zeta potential and shear plane for montmorillonite.

Effect of different treatments on electrokinetic remediation of Zn, Pb and Cd from a contaminated calcareous soil

Electrokinetic remediation is a promising method to decontamination of the heavy metals from soils. In this paper, the remediation of a contaminated calcareous soil with Zn, Cd and Pb sampled from around Zanjan province of Iran, was investigated using electrokinetic method. In this paper, the soil contain a high concentration of Zn (1400 mg·kg−1), Cd (15 mg·kg−1) and Pb (250 mg·kg−1). Electrokinetic decontamination consists of two series of experiments as follows: (1) the effect of five treatments including the use of distilled water, acetic acid and EDTA electrolyte solutions, and approaching anodes systems, and the circulation flow of electrolyte at two different voltage gradient (i.e. 1.33 and 2.66 V·cm−1), and (2) the effect of moisture content (saturated, FC and 0.7FC, FC indicated soil moisture at “Field Capacity”) with a voltage gradient of 1.33 V·cm−1. After applying electric current for 5 days, the results of experiments indicated that the removal efficiency of heavy metals can be increased by raising the voltage gradient. In this matter, the highest remediation can be observed among different treatments in EDTA (Ethylene diamine tetra acetic acid) treatment (40.11%, 43.10% and 24.7% for Zn, Cd and Pb, respectively). Moreover, the heavy metals removal at the saturated moisture was at the highest level so that 32.62% cadmium, 31.33% zinc and 18.82% lead being removed after 120 h of electric current application. By decreasing moisture to 0.7FC, the removal percentage for the three heavy metals obtained 20.97%, 18.44% and 12.25%, respectively. Furthermore, Cd had the highest removal, and Zn and Pb were next among the three heavy metals in question.

Innovative thermal and physico-chemical treatments for the clean-up of marine sediments dredged from the Augusta Bay (Southern Italy)

The main objective of this study was to compare the energy cost-effectiveness of two innovative techniques, namely microwave (MW) heating and electrokinetic (EK) decontamination for the successful remediation of highly Hg-contaminated marine sediments from Augusta Bay (Sicily, Italy).Bench-scale experiments were conducted and obtained results were used to elaborate energy and economic considerations aimed at selecting the most effective and economic approach.Results revealed that without any appropriate conditioning agents, very poor contaminant mobilization can be achieved by EK due to the high percentage of carbonates, as sediment mineral, and high organic matter and sulphides. The best Hg-removal (∼71% in 400 h) was achieved using both methylglycinediacetic acid (MGDA) and polyoxyethylene (20) sorbitan monooleate (Tween 80) as processing agents. Related Hg residual concentrations exceed the desired regulatory limit of 1 mg kg−1 for Augusta Bay. Simulated MW heating showed the achievement of a very rapid sediment temperature increase (∼64 °C min−1, maximum ∼450 °C), mainly due to the mineral composition of the sediments and their high salinity. This jointly with the addition of both MGDA and Tween 80, led to a very low residual Hg concentration of 0.56 mg kg−1 (R = ∼99%) after 7-min treatment.Calculations from energy and economic analysis revealed that a specific energy consumption of 6.73 kWh ton−1, which corresponds to an energy cost of 0.81 € ton−1, is required for the EK, whereas slightly higher values (32.97 kWh ton−1 and 3.96 € ton−1) were assessed for MW heating. Therefore, the higher Hg-removal obtainable in such a short remediation time by MW heating along with its with other advantages offset a low specific energy cost increase, making this technique a preferable choice for the remediation of Hg-contaminated marine sediments such as those present in Augusta Bay.

Editors' Choice—Review—Electro-Kinetic Decontamination of Radioactive Concrete Waste from Nuclear Power Plants

Electro-kinetic decontamination has been studied for radioactive concrete of nuclear power plants because of its effective removal of contaminants from deep inside concrete. Although many experiments have been conducted, a systematic comparison has been scarcely conducted. By a thorough review, this study reveals how different conditions of electro-kinetic decontamination changes the decontamination ratio and rate of Cs and Co. The tested conditions include cell configurations (i.e., geometry of concrete waste, electrode materials, and volume of solutions) and operating conditions (i.e., types and concentrations of solutions, electric field, and test duration). The careful analysis suggests the important roles of pH in electrolytic solution, electric field, and pre-treatment. We also discuss the chemical conditions under which the decontamination of Cs and Co was optimized in the presence of an applied voltage. In addition, we critically review the conditions of simulated concrete samples in the previous experiments in comparison with actual nuclear plant data.

Removal of heavy metal from sludge by the combined application of a biodegradable biosurfactant and complexing agent in enhanced electrokinetic treatment

In this work, the heavy metal removal potentiality of an electrokinetic (EK) decontamination treatment enhanced by a biodegradable complexing agent Tetrasodium of N, N-bis (carboxymethyl) glutamic acid (GLDA) also in combination with a biodegradable biosurfactant (rhamnolipid) was investigated to decontaminate heavy metals from the sludge. The main results explored that the nature of sludge and their interactions with different improving agents significantly influenced the electrokinetic removal processes. A general increase of pH values from anode to cathode in the sludge-cell was observed due to the strong buffering capacity of carbonates. Compared with the deionized water, the use of GLDA as an electrolyte, Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 53.2 ± 3.12%, 67.4 ± 3.45%, 59.2 ± 4.78%, 45.4 ± 4.15%, 72.8 ± 3.68% and 45.0 ± 4.85%, respectively, whereas a further improvement heavy metals removal efficiencies (Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 64.8 ± 2.34%, 56.8 ± 4.12%, 49.4 ± 4.45%, 46.6 ± 2.35%, 60.4 ± 3.45% and 69.6 ± 3.54%, respectively) were achieved by repalcing rhamnolipid as the electrolyte. Significantly higher removal efficiencies (Cu, Zn, Cr, Pb, Ni and Mn removal efficiencies were 70.6 ± 3.41%, 82.2 ± 5.21%, 89.0 ± 3.34%, 60.0 ± 4.67%, 88.4 ± 4.43% and 70.0 ± 3.51%, respectively) were obtained by the simultaneous use of GLDA and rhamnolipid due to their synergic action in electrokinetic process.

Removal of mercury from marine sediments by the combined application of a biodegradable non-ionic surfactant and complexing agent in enhanced-electrokinetic treatment

In this work, the Hg removal potentiality of an electrokinetic (EK) decontamination treatment enhanced by a biodegradable complexing agent (MGDA) also in combination with a biodegradable surfactant (Tween® 80) was investigated to decontaminate heavily contaminated marine sediments. The main results revealed that the nature of sediments and their interactions with different enhancing agents significantly influenced the remediation processes. A general increase of pH values along the sediment specimen was observed due to the strong buffering capacity of the carbonates, which are the main constituent minerals. This, in combination with the high organic matter and sulphide sediment content, resulted in very poor contaminant mobilization without any appropriate conditioning agents. The use of EDTA as a processing fluid resulted in a modest increase in Hg removal of ∼15%, whereas a further improvement in the Hg removal rate (∼39%) was achieved by replacing EDTA with MGDA as the anodic solution in response to its ability to form stable negative complexes with mercury, which can be moved towards the anode. A significantly higher Hg-removal of ∼71% was obtained by the simultaneous use of MGDA and Tween® 80 due to their synergic action in remedial processes and, especially, due to the improved selective action of the non-ionic surfactant adopted in favour of organo-Hg-complex removal. Compared with other Hg-removal technologies, the investigated enhanced-EK treatment allows the achievement of remediation targets, which can hardly met by one-stage processes. The data can be useful for predicting the remediation activity responses, as well as for guiding the design and scaling-up of EK treatment of Hg-contaminated sediments. In addition, the knowledge of the investigated Hg-removal mechanism can provide basic information, which is helpful for improving the development of further novel enhanced-EK technologies.

Surfactant and MGDA enhanced – Electrokinetic treatment for the simultaneous removal of mercury and PAHs from marine sediments

Abstract Mercury (Hg) and Hg-PAH removal effectiveness of several electrokinetic (EK) decontamination treatments, including the combined use of eco-friendly enhancing agents, was investigated in this work as a potential remedial treatment of heavily contaminated marine sediments. After a 400-h EK treatment, main results revealed a very poor Hg mobilization without the use of an appropriate conditioning agent, mainly due to the strong Hg-bounds with carbonates, organic matter and sulphides, which were present at high concentrations. The use of EDTA as processing fluid resulted in a slight improvement of Hg removal (∼15%). A further increase in Hg removal rate of ∼39% can be achieved with methylglycinediacetic acid (MGDA) as anodic solution. The best Hg-removal of ∼71% was obtained by means of the simultaneous use of MGDA and Tween® 80 due to their synergistic action in remedial processes. The same type of treatment led to a slightly lower total Hg-removal of ∼67% when a shorter time of 240 h was considered. In the case Hg and PAHs as sediment co-contaminants, results revealed a total PAH-removal of 59.45%. The co-presence of PAHs significantly affected the electric current circulating in the system and the electrosmotic values, leading to a reduction of about 5% in Hg removal respect to the case where PAHs were not present in the sediments. Nevertheless, the combined application of Tween® 80 and MGDA in enhanced-EK treatment allows the possibility to successfully remove both highly persistent Hg and PAHs from marine sediments with high removal percentages. Obtained data can be useful for further enhanced EK treatments of sediments contaminated with Hg and PAHs, as well as providing basic information for future cost analysis.

Characteristics of Cement Solidification of Metal Hydroxide Waste

To perform the permanent disposal of metal hydroxide waste from electro-kinetic decontamination, it is necessary to secure the technology for its solidification. The integrity tests on the fabricated solidification should also meet the criteria of the Korea Radioactive Waste Agency. We carried out the solidification of metal hydroxide waste using cement solidification. The integrity tests such as the compressive strength, immersion, leach, and irradiation tests on the fabricated cement solidifications were performed. It was also confirmed that these requirements of the criteria of Korea Radioactive Waste Agency on these cement solidifications were met. The microstructures of all the cement solidifications were analyzed and discussed.

Электрокинетическая очистка тонкодисперсных глинистых почв, загрязненных хлорорганическими соединениями

Электрокинетическая очистка тонкодисперсных глинистых почв, загрязненных хлорорганическими соединениями

Removal of uranium from contaminated soil using indoor electrokinetic decontamination

Indoor electrokinetic decontamination equipment was manufactured to treat 1.2 tons of uranium-contaminated soil. For a reduction of waste electrolyte and metal oxide, waste electrolyte was reused and the optimum pH was adjusted to minimize metal oxide volume in the cathode chamber. It was found that the optimum pH of the waste electrolyte in a cathode chamber was below 2.35 at 25 °C. When the initial uranium concentrations in the soils were 7.0–27.0 Bq/g, the reuse periods of waste electrolyte required for uranium concentrations in the soils to reach below 5.0 Bq/g were 5–25 days. In addition, when the initial concentrations in the soils were 7.0–20.0 Bq/g, the periods required to reach below the clearance concentration level were 25–40 days.

Decontamination of Soil Contaminated with Cesium using Electrokinetic-electrodialytic Method

The soil contaminated with cesium was sampled at an area near a nuclear facility in Korea. Electrokinetic decontamination equipment and electrokinetic-elctrodialytic decontamination equipment were manufactured to decontaminate the contaminated soil. The removal efficiency according to the lapsed time by the electrokinetic decontamination equipment and the electrokinetic-elctrodialytic decontamination equipment was investigated through several experiments. The difference between the removal efficiency of the electrokinetic-elctrodialytic equipment without an anion exchange membrane and that with an anion exchange membrane was investigated through several experiments. The removal efficiency of 137Cs+ from soil by electrokinetic-electrodialytic decontamination technology was higher than that of 137Cs+ from soil by electrokinetic decontamination technology. The removal efficiency of 137Cs+ was sharply reduced after 7 days on using electrokinetic decontamination, because the 137Cs+ on the surface of the soil particles had almost been removed for 7 days. The removal efficiency of 137Cs+ was increased after 7 days on using electrokinetic-electrodialytic decontamination with soil stirring. The soil stirring accelerated the desorption of cesium ions from soil and an anion exchange membrane shortened the period for removing cesium from the soil cell by preventing the influx of cesium ions into the anode room. The more the initial radioactivity concentration of soil increased, the more the removal efficiency of 137Cs+ from soil increased. When the electrokinetic-electrodialytic decontamination period of 0.3–7.0 days elapsed, 137Cs+ in the soil was removed by about 12–83%. When the electrokinetic-electrodialytic decontamination period of 10–21 days elapsed, the 137Cs+ in soil was removed by about 91–97%.

Precipitation-filtering technology for uranium waste solution generated on washing-electrokinetic decontamination

Large volumes of uranium waste solution are generated during the operation of washing-electrokinetic decontamination equipment used to remove uranium from radioactive soil. A treatment technology for uranium waste solution generated upon washing-electrokinetic decontamination for soil contaminated with uranium has been developed. The results of laboratory-size precipitation experiments were as follows. The total amount of metal precipitation by NaOH for waste solution was highest at pH 11. Ca(II), K(I), and Al(III) ions in the supernatant partially remained after precipitation, whereas the concentration of uranium in the supernatant was below 0.2ppm. Also, when NaOH was used as a precipitant, the majority of the K(I) ions in the treated solution remained. The problem of CaO is to need a long dissolution time in the precipitation tank, while Ca(OH)2 can save a dissolution time. However, the volume of the waste solution generated when using Ca(OH)2 increased by 8mL/100mL (waste solution) compared to that generated when using CaO. NaOH precipitant required lower an injection volume lower than that required for Ca(OH)2 or CaO. When CaO was used as a precipitant, the uranium radioactivity in the treated solution at pH 11 reached its lowest value, compared to values of uranium radioactivity at pH 9 and pH 5. Also, the uranium radioactivity in the treated solution upon injection of 0.2g of alum with CaO or Ca(OH)2 was lower than that upon injection of 0.4g of alum. The results of industrial scale precipitation experiments were as follows. When NaOH was injected as a precipitant, the uranium radioactivity in the treated solution was the lowest of the three precipitants, and the dried sludge volume was the smallest. However, when the treated solution was recycled as a washing solution or electrolyte, K(I) ions can be accumulated in the treated solution. When Ca(OH)2 was injected as a precipitant, the volume of the generated waste solution was found to increase. After drying for 24h, the volume of sludge was reduced to 35% of the initial sludge volume. Meanwhile, a recycling process diagram for the volume reduction of waste solution generated from soil washing and electrokinetic decontamination was developed through experiments.

Electrokinetics and soil decontamination: concepts and overview (Review)

Electrokinetic decontamination and extraction have been proven to be one of the most viable, cost effective and emerging techniques in removing contaminants, especially heavy metals from soils for about last five decades. Basic concepts and an overview of the electrokinetic extraction processes and their potential applications in geotechnical and geoenvironmental engineering have been reviewed based on the literature and presented in this paper. Primarily, theoretical and laboratory experimental studies related to electroreclamation of soils are summarised in brief with basic concepts of electrokinetic processes. The paper has been divided into different sections that include history of electrokinetics, background and concepts, modelling, parameter effects, instrumentation, contaminant extraction, field applications, and summary and recommendation. Based on the review it is obvious that the field application of electrokinetic technology to remediate heavy metal contaminated soils /sediments is very limited and site specific. Additional laboratory studies and more pilot- and full-scale information from field applications are critical to the further understanding of the technology and to customize the process in different field conditions.

Decontamination of gravels contaminated with uranium

Gravel washing equipment and electrokinetic–electrodialytic decontamination equipment were manufactured to decontaminate gravel contaminated with uranium. The removal efficiency according to the gravel size and weight and the removal efficiency according to the lapsed time using the manufactured equipment were investigated through several experiments. The volume of gravel in the high uranium concentration group was about 10%, the rock types of which were quartz, lamprophyre, and schist. The larger the gravel size, the higher the contaminated concentration of gravel. The average uranium (238U) concentration of gravel after the first washing was about 1.45Bq/g, and the average removal efficiency of gravel after the third washing was about 37%. In addition, the removal efficiency of the contaminated gravel was not related to its size. The contaminated concentration of the gravel decreased with an increasing gravel weight. In addition, the removal efficiency of contaminated gravel was not related to its weight. When the electrokinetic–electrodialytic decontamination period of 5days, 10days, 15days, and 20days elapsed, the 238U in the gravel was removed by about 40%, 65%, 72%, and 81%. The more the electrokinetic–electrodialytic decontamination time elapsed, the more the removal efficiency ratio of 238U decreased. Finally, the gravel with a size of less than 10cm was treated by soil washing and electrokinetic decontamination methods with soil, and gravel with size of more than 10cm but less than 20cm was treated by gravel washing and electrokinetic–electrodialytic decontamination methods. Gravel with a size of more than 20cm is treated by a gravel washing method, and gravel contaminated with a high concentration of uranium was treated by crushing and ball mill washing methods.

동전기제염장치에서 발생한 폐액의 재사용을 위한 개선된 처리기술

우라늄으로 오염된 토양을 복원하기 위해 실규모의 동전기제염장치로 제염하는 과정에서 많은 산폐액이 발생한다. 발생한 산폐액에 CaO를 가해 우라늄수산화물을 침전시켜 여과한 다음, 방사성 폐액을 줄이기 위하여 이 용액을 재사용하였다. 그러나 이 용액을 동전기에 재사용할 경우, 높은 농도의 칼슘 때문에 양극실에서 음극실로 용액이동 속도가 감소하여 여과포의 약화, 전선 부식, 음극면에 산화물 부착 등의 문제점이 발생하였다. 이 문제들을 해결하기 위하여 재생액에 황산을 넣어 <TEX>$CaSO_4$</TEX>로 침전시켜 칼슘을 제거하였다. 칼슘이 제거된 재생액을 사용하여 소형 동전기 장치에서 20 일간 토양제염 실험을 수행한 결과는 세척후 토양내 우라늄 잔류 농도가 0.35 Bq/g로 감소하였으며, 이는 증류수 제염한 결과와 유사하게 나타났다. A large amount of acidic waste solution is generated from the practical electrokinetic decontamination equipments for the remediation of soil contaminated with uranium. After filtration of uranium hydroxides formed by adding CaO into the waste solution, the filtrate was recycled in order to reduce the volume of waste solution. However, when the filtrate was used in an electrokinetic equipment, the low permeability of the filtrate from anode cell to cathode cell due to a high concentration of calcium made several problems such as the weakening of a fabric tamis, the corrosion of electric wire and the adhension of metallic oxides to the surface of cathode electrode. To solve these problems, sulfuric acid was added into the filtrate and calcium in the solution was removed as <TEX>$CaSO_4$</TEX> precipitate. A decontamination test using a small electrokinetic equipment for 20 days indicated that Ca-removed waste solution decreased uranium concentration of the waste soil to 0.35 Bq/g, which is a similar to a decontamination result obtained by distilled water.

A radioanalytical phantom for assessing the efficacy of electrokinetic decontamination of entrained radioactivity within concrete media

A phantom for the evaluation of electrokinetic remediation of radioactive species from water saturated concrete is described. The phantom has been designed to be a general analogue for environments where structural concrete is saturated by radioactive aqueous solutions and where electrokinetic remediation may be deployed. It is also a specific analogue for the walls of storage ponds for legacy spend nuclear fuel pins where the pond water comprises a large volume of hazardous active waste that may penetrate the pond wall. The fabricated phantom was evaluated using a fixed electrical potential to monitor the rate of cationic transport of K+ through concrete samples of different thickness (20 and 35 mm respectively). Results of the evaluation show K+ diffusion coefficients of 5.20 × 10−13 and 7.61 × 10−13 m2 s−1 for the 20 mm and 35 mm samples, consistent with those seen in literature for the transport of caesium through concrete of similar thickness. The phantom offers a means of experimental validation of computational electrokinetic models as well as providing a basis to test the effects of electrode material on ionic transport rates, to interrogate the effects of pH on all components of the system, and as a basis for instruction, education and training in nuclear decommissioning and waste treatment.

土壌pHを中性領域に保った条件下におけるカチオン系金属汚染土壌の動電学的浄化処理

土壌pHを中性領域に保った条件下におけるカチオン系金属汚染土壌の動電学的浄化処理

Cs-137 and Cs-134 removal from radioactive ash using washing–electrokinetic equipment

To remove more than 85% of 137Cs and 134Cs from radioactive ash through a washing–electrokinetic technology, many washing and electrokinetic experiments at a laboratory scale were carried out to obtain the optimum reagent type, its concentration, and the decontamination time. Pilot-sized washing–electrokinetic equipment suitable to the radioactive ash generated in Fukushima Japan was manufactured. In addition, to remove more than 93% of 137Cs and 134Cs from the washed ash, electrokinetic decontamination experiments using 50L pilot-sized electrokinetic equipment were carried out. When the initial 137Cs concentration of radioactive ash was 41.8Bq/g, the removal efficiency of 137Cs in the radioactive ash after three washings was 89.1%. Additionally, the required electrokinetic decontamination time to decontaminate the 137Cs concentration below 2.0Bq/g was 10days, and at that time, the removal efficiency of the 137Cs was 95.3%. Also, when the initial 134Cs concentration of radioactive ash was 31.5Bq/g, the removal efficiency of 134Cs in the radioactive ash after three washings was 89.0%. In addition, the required electrokinetic decontamination time to decontaminate the 134Cs concentration below 2.0Bq/g was 8days, and at that time, the removal efficiency of 137Cs was 94.4%. It was conclusively found that 87–89% of the 134Cs and 137Cs in the radioactive ash was removed by three washings, and the radioactive ash contaminated with 30–40Bq/g of 134Cs and 137Cs needs to be decontaminated with electrokinetic equipment for 8–10days after three washings to reach below 2.0Bq/g.

Enhancement of electrokinetic decontamination with EDTA

The effect of ethylenediaminetetraacetic acid (EDTA) during electrokinetic decontamination (EKD) was investigated in this research. EDTA is a ligand that can form soluble complexes with precipitated heavy metals inside soil pores. Millpond sludge, primarily contaminated with lead (Pb) and zinc (Zn), was subjected to EKD with and without the presence of EDTA. Dilute EDTA solutions with strengths of 0.05 M and 0.125 M were injected into the millpond sludge by electroosmosis. Several beneficial effects of using EDTA were observed in this research. One was that the presence of EDTA substantially increased the electroosmotic (EO) flow in the millpond sludge indicating that it could significantly reduce the duration of EKD. Another advantage was that a significantly higher percentage of Pb and Zn removal was achieved from the solid phase due to the complexation of EDTA with these heavy metals. Also, EDTA was able to prevent the precipitation of metals at the cathode electrode, typically observed in EKD process.