In situ removal of copper from sediments by a galvanic cell

This study dealt with in situ removal of copper from sediments through an electrokinetic (EK) process driven by a galvanic cell. Iron (Fe) and carbon (C) were placed separately and connected with a conductive wire. Polluted sediments were put between them and water was filled above the sediments. The galvanic cell was thus formed due to the different electrode potentials of Fe and C. The cell could remove the pollutants in the sediments by electromigration and/or electroosmosis. Results showed that a weak voltage less than 1V was formed by the galvanic cell. The voltage decreased with the increase of time. A slight increase of sediment pH from the anode (Fe) to the cathode (C) was observed. The presence of supernatant water inhibited the variation of sediment pH because H(+) and OH(-) could diffuse into the water. The removal of copper was affected by the sediment pH and the distribution of electrolyte in sediment and supernatant water. Lower pH led to higher removal efficiency. More electrolyte in the sediment and/or less electrolyte in the supernatant water favored the removal of copper. The major removal mechanism was proposed on the basis of the desorption of copper from sediment to pore solution and the subsequent electromigration of copper from the anode to the cathode. The diffusion of copper from sediment to supernatant water was negligible.     

场地环境污染的电动修复技术研究现状与趋势

在综述国内外场地污染土壤电动修复技术的研究现状和趋势的基础上,针对场地土壤电动修复中常见问题,包括电极设置方式、化学增强试剂的选择、土壤类型和污染程度等影响去除效率的因素及处理效果和能耗等进行阐述,探讨当前我国场地土壤电动修复技术研发的重点,以促进场地污染土壤修复技术的发展和应用.     

动电技术去除城市污泥中重金属的可行性探讨

本文简要介绍了我国城市污泥的处理处置和利用现状及动电技术去除重金属的基本原理,分析动电技术处理土壤中重金属的国内外的试验研究和应用情况,对动电技术处理城市污泥中重金属的可行性进行探讨,认为动电技术去除城市污泥中的重金属具有可行性,并提出了今后研究的方向.     

Electrokinetic-enhanced phytoremediation of soils: Status and opportunities

Phytoremediation is a sustainable process in which green plants are used for the removal or elimination of contaminants in soils. Both organic and inorganic contaminants can be removed or degraded by growing plants by several mechanisms, namely phytoaccumulation, phytostabilization, phytodegradation, rhizofiltration and rhizodegradation. Phytoremediation has several advantages: it can be applied in situ over large areas, the cost is low, and the soil does not undergo significant damages. However, the restoration of a contaminated site by phytoremediation requires a long treatment time since the remediation depends on the growth and the biological cycles of the plant. It is only applicable for shallow depths within the reach of the roots, and the remediation efficiency largely depends on the physico-chemical properties of the soil and the bioavailability of the contaminants. The combination of phytoremediation and electrokinetics has been proposed in an attempt to avoid, in part, the limitations of phytoremediation. Basically, the coupled phytoremediation–electrokinetic technology consists of the application of a low intensity electric field to the contaminated soil in the vicinity of growing plants. The electric field may enhance the removal of the contaminants by increasing the bioavailability of the contaminants. Variables that affect the coupled technology are: the use of AC or DC current, voltage level and mode of voltage application (continuous or periodic), soil pH evolution, and the addition of facilitating agents to enhance the mobility and bioavailability of the contaminants. Several technical and practical challenges still remain that must be overcome through future research for successful application of this coupled technology at actual field sites.     

Chelating agent-assisted electrokinetic removal of cadmium, lead and copper from contaminated soils

An integrated experimental program was conducted to remove Cd, Pb and Cu from contaminated soil. The chelate agents nitrilotriacetic acid (NTA), diethylenetriamine pentaacetic acid (DTPA) and ethyleneglycol tetraacetic acid (EGTA) were used as washing solutions under different pH conditions and concentrations. Results showed that the extraction efficiency for Cd in decreasing order was NTA > EGTA > DTPA, while for Pb and Cu it was DTPA > NTA > EGTA. The use of higher chelate concentrations did not necessarily result in greater extraction efficiency. Electrokinetic remediation was applied by conditioning anolyte-catholyte pH to neutral values in order to avoid any potential alterations to the physicochemical soil properties. The removal efficiency for Cd was 65-95%, for Cu 15-60%, but for Pb was less than 20%. The phytotoxicity of the treated soil showed that the soil samples from the anode section were less phytotoxic than the untreated soil, but the phytotoxicity was increased in the samples from the cathode section.     

An assessment of the effectiveness and impact of electrokinetic remediation for pyrene-contaminated soil

The effectiveness of electrokinetic remediation for pyrene-contaminated soil was investigated by an anode-cathode separated system using a salt bridge. The applied constant voltage was 24 V and the electrode gap was 24 cm. Two types of soil （sandy soil and loam soil） were selected because of their different conductive capabilities. The initial concentrations of pyrene in these soil samples were 261.3 mg/kg sandy soil and 259.8 mg/kg loam soil After treatment of the sandy soil and loam soil for seven days, 56.8% and 20.1% of the pyrene had been removed respectively. Under the same power supply voltage, the removal of the pollutant from the sandy soil was greater than that from the loam soil, due to the higher current and lower pH. Further analysis revealed that the effectiveness of electrokinetic remediation was affected by the energy expenditure, and was associated with changes in soil properties.     

Electrochemical remediation of phenanthrene from contaminated kaolinite

In this work a two-stage process combining soil electrokinetic remediation and liquid electrochemical oxidation for the remediation of polluted soil with organic compounds has been developed and evaluated using phenanthrene-spiked kaolinite. Application of an unenhanced electrokinetic process resulted in negligible removal of phenanthrene from the kaolinite sample. Addition of co-solvents and electrolyte to the processing fluid used in the electrode chambers enhanced phenanthrene desorption from the kaolinite matrix and favoured electro-osmotic flow. Near-complete removal of phenanthrene was achieved using Na₂SO₄ and ethanol in the processing fluid. Phenanthrene was transported towards the cathode chamber where it was collected. The cathodic solution containing the pollutant was treated by electrochemical oxidation; complete degradation of phenanthrene occurred after 9 h using Na₂SO₄ as electrolyte.     

Combined use of a transformed red mud reactive barrier and electrokinetics for remediation of Cr/As contaminated soil

A reactive barrier (RB) of transformed red mud (TRM), a by-product of the refinement of bauxite in alumina production, was placed adjacent to the anode of an electrokinetic (EK) system with the aim of enhancing removal of chromium or arsenic, added singly to a low permeability clayey soil, and favouring entrapment. The innovative study focused on evaluation of the synergic interaction between the EK system and the RB, and of the efficiency when compared to traditional EK remediation (control tests). The results obtained underlined the successful outcome of treatment of the Cr(VI)-contaminated soil. In presence of the TRM RB, 19.4% wt. of total Cr content was detected in the anolyte and 20.6% wt. trapped in the anodic RB after 6 d, versus 6.6% wt. in the anolyte and 8.8% wt. in the soil adjacent to the anode following the control run without RB. On increasing duration of treatment up to 12 d, 60.8% wt. of total initial Cr was found in the anolyte and 25.5% wt. trapped in the RB, versus 9.1% wt. and 5.3% wt., respectively, after a control run of the same duration. Finally, on increasing the mass of TRM in the RB, 60.6% wt. of initial Cr content was found to have accumulated in the RB, with Cr being completely absent from the anodic chamber. Conversely, combined treatment was much less effective on As contaminated soil, at least under the operative conditions applied. Low initial As concentration and interference with iron oxides in the soil were likely the reasons underlying low efficiency while attempting As decontamination.     

Influence of electrical fields (AC and DC) on phytoremediation of metal polluted soils with rapeseed (Brassica napus) and tobacco (Nicotiana tabacum)

The combined use of electrokinetic remediation and phytoremediation to decontaminate soil polluted with heavy metals has been demonstrated in a laboratory-scale experiment. The plants species selected were rapeseed and tobacco. Three kinds of soil were used: un-contaminated soil from forest area (S1), artificially contaminated soil with 15 mg kg⁻¹ Cd (S2) and multi-contaminated soil with Cd, Zn and Pb from an industrial area (S3). Three treatment conditions were applied to the plants growing in the experimental vessels: control (no electrical field), alternating current electrical field (AC, 1 V cm⁻¹) and direct current electrical field (DC, 1 V cm⁻¹) with switching polarity every 3 h. The electrical fields were applied for 30 d for rapeseed and 90 d for tobacco, each experiment had three replicates. After a total of 90 d growth for rapeseed and of 180 d for tobacco, the plants were harvested. The pH variation from anode to cathode was eliminated by switching the polarity of the DC field. The plants reacted differently under the applied electrical field. Rapeseed biomass was enhanced under the AC field and no negative effect was found under DC field. However, no enhancement of the tobacco biomass under the AC treatment was found. The DC field had a negative influence on biomass production on tobacco plants. In general, Cd content was higher in both species growing in S2 treated with AC field compared to the control. Metal uptake (Cd, Cu, Zn and Pb) per rapeseed plant shoot was enhanced by the application of AC field in all soils.     

The feasibility of decontamination of reduced saline sediments from copper using the electrokinetic process

The remediation of metal contamination in estuarine and reduced sediments is another challenge for the electrokinetic process. Problems result from the complex chemical composition of saline reduced sediments. In the experiments described here copper was added into saline reduced sediments to simulate the natural situation. Two constant voltages were applied across the electrokinetic cell to investigate the effect of an increase in potential difference on the electrokinetic process. Acetic acid at pH 6 and 4 was also added to the cathode in separate experiments to enhance copper removal. The results from this study showed that in the unenhanced experiments most of copper remained in the soil and was unaffected by the electrokinetic process. At the end of unenhanced electrokinetic experiments, the copper concentration was found only to be slightly changed in the anode region. Up to 21% of the copper was found precipitated near the anode when the applied voltage was 10V and this increased to 25% when the applied voltage was 7V. In the enhanced electrokinetic experiments up to 98% of copper was removed from section 1 and precipitated again in sections 2 and 3. This indicates that a significant amount copper removal from the saline sediments may be achieved by the enhanced electrokinetic process.