Performance Evaluation of Two-Stage Electrokinetic Washing as Soil Remediation Method for Lead Removal using Different Wash Solutions

Potential mechanisms contributing to the high cadmium removal efficiency from contaminated soil by using effective microorganisms as novel electrolyte in electrokinetic remediation applications

In this study, we tested the ability of a solution of effective microorganisms (EM) to remove cadmium from soil. Experimental results revealed that EM had an overall cadmium removal efficiency of 90.5% after 7 days of electrokinetic (EK) treatment. During EK treatment, EM exhibited a low initial pH of 3.6 and a high conductivity of 7.0 mS/m; therefore, they reduced the pH of the anode after an electric field was applied. EM had a surface tension of 50.3 dyne/cm and exhibited biosurfactant property in the EK experiments. The cadmium removal efficiency of EM in soil was compared with that of tap water, citric acid, and ethylenediaminetetraacetic acid (EDTA). The results revealed that after 7 days of EK treatment, EM had a higher cadmium removal efficiency than did citric acid (72.3%), EDTA (75.4%), and tap water (21.7%). This result can be partly attributed to the biosurfactant property of EM, which enables them to penetrate deeply into the soil matrix and thus dissolve a high quantity of pollutants. Overall, the results of this study indicate that EM can serve as an economic and efficient biosurfactant for removing cadmium from soil in EK applications.

Mechanistic insights into soil heavy metals desorption by biodegradable polyelectrolyte under electric field

In this study, we firstly used alginate to enhance an electrokinetic technology to remediate soil contaminated with divalent heavy metals (Pb²⁺, Cu²⁺, Zn²⁺). The mechanisms of alginate-associated migration of metal ions in electric field were confirmed. Alginate resulted in a high electrical current during electrokinetic process, and soil conductivity also increased after remediation. Obvious changes in both electroosmotic flow and soil pH were observed. Moreover, these factors were affected by increasing alginate dosage. The highest Cu (95.82%) and Zn (97.33%) removal efficiencies were obtained by introducing 1 wt% alginate. Alginate can desorb Cu²⁺ and Zn²⁺ ions from soil by forming unstable gels, which could be dissociated through electrolysis. However, Pb²⁺ ions did not easily migrate out of the contaminated soil. The density functional theory (DFT) calculations show Pb²⁺ ions could form a more stable coordination sphere in metal complexes than Cu²⁺ and Zn²⁺ ions. The metal removal efficiency was decreased by increasing alginate dosage at a high level. More alginate could provide more carboxyl ligands for divalent metal ions to stabilize gels, which were difficult to dissociate by electrolysis. In summary, the results indicate it is potential for introducing alginate into an electrokinetic system to remediate Cu- and Zn- contaminated soil.

Remediation of heavy metal-contaminated soils by electrokinetic technology: Mechanisms and applicability

Electrokinetic remediation is a widely admitted technology forrectifying heavy metal-contaminated soil. Various technologies have been effectively developed to improve the metal removal efficiency of contaminated soil by electrochemical treatment alone or in combination with other remediation technologies. The working components for electrokinetic system, such as supplying power for electric fields, installing electrodes to generate electric fields, introducing electrolytes and other potential materials as a reactive medium are crucial. This review focuses on the specific functions of the working components in electrokinetic systems and their effects on the efficiency of heavy metal removal using electrochemical process. The advancements in working components were systematically summarized, such as power for electric fields, electrodes, electrolytes and ion exchange membrane, which have various impacts on the effectiveness of electrokinetic remediation. Additionally, this study introduces the application of dominating technologies at present coupled with electrokinetics. Overall, a judicious design and reasonable operation in the application of electrokinetic-coupled remediation should be implemented to enhance the removal process of heavy metals from contaminated soil.

Pb2+ ions mobility perturbation by iron particles during electrokinetic remediation of contaminated soil

Electrokinetic (EK) remediation is one of the most useful approaches for de-contamination of soils. However, it is unclear that how and when the electrokinetic remediation gives advantages over other remediation techniques in soil. This study was designed to find the influence of Fe²⁺ particles on the mobility of Pb²⁺ ions, during electrokinetic remediation, in soil contaminated purposely by lead nitrate Pb(NO₃)₂. Two types of electrokinetic experiments were performed, by using iron and graphite electrodes. The Fe²⁺ ions from the iron electrodes, produced due to acidic environment in anode compartment, affected the mobility of lead particles by precipitating as Fe(OH)₂. Fe²⁺ ions enhance the adsorption of lead ions in soil. The results show Fe²⁺ ions of lower ionic conductivity decreased mobility of other particles in soil. Electrokinetic remediation for up to 120 h with iron electrodes is shown to be less effective for removal of lead. In contrast, graphite electrodes were 15 times more effective in lead removal from soil.

Conceptual design and experiments of electrochemistry-flushing technology for the remediation of historically Cr(Ⅵ)-contaminated soil

A conceptual design and experiments, electrochemistry-flushing (E-flushing), using electrochemistry to enhance flushing efficiency for the remediation of Cr(Ⅵ)-contaminated soil is presented. The rector contained three compartments vertically superposed. The upper was airtight cathode compartment containing an iron-cathode. The middle was soil layer. The bottom was anode compartment containing an iron-anode and connected to a container by circulation pumps. H2 and OH(-) ions were produced at cathode. H2 increased the gas pressure in cathode compartment and drove flushing solution into soil layer forming flushing process. OH(-) ions entered into soil layer by eletromigration and hydraulic flow to enhance the desorption of Cr(Ⅵ). High potential gradient was applied to accelerate the electromigration of desorbed Cr(Ⅵ) ions and produced joule heat to increase soil temperature to enhance Cr(Ⅵ) desorption. In anode compartment, Fe(2+) ions produced at iron-anode reduced the desorbed Cr(Ⅵ) into Cr(3+) ions, which reacted with OH(-) ions forming Cr(OH)3. Experimental results show that Cr(Ⅵ) removal efficiency of E-flushing experiments was more than double of flushing experiments and reached the maximum of removal efficiency determined by desorption kinetics. All electrochemistry processes were positively used in E-flushing technology.