Specific Energy Requirements in Electrokinetic Remediation

Experimental and Numerical studies on remediation of mixed metal-contaminated sediments by electrokinetics focusing on fractionation changes

Electrokinetic remediation technique is widely applied for the removal of heavy metal from contaminated soil, but the soil buffering capacity and fractionation of heavy metals mainly affect the cost and duration of the treatment. This study aims to treat heavy metal-contaminated sediments by electrokinetic remediation (EKR) technique by using various enhancing agents such as EDTA, [Formula: see text], HCI, [Formula: see text], acetic acid and citric acid for optimizing the cost and treatment duration. The optimum molar concentration of enhancing agent for treatment was estimated by batch experiments to maximize the dissolution of target heavy metals and reduce the dissolution of earth metals (Fe, Al and Ca) to maintain soil health. The EKR experiments were performed up to 15 days with the above enhancing agents to reduce the risk associated with heavy metals and the selection of enhancing agents based on removal efficiency was found to be in an order of EDTA > citric acid > acetic acid > [Formula: see text] > HCl [Formula: see text] [Formula: see text]. Also, a numerical model has been developed by incorporating main electrokinetic transport phenomena (electromigration and electroosmosis) and geochemical processes for the prediction of treatment duration and to scale up the EKR process. The model predicts well with experimental heavy metal removal with a MAPD of [Formula: see text] 2-18 %. The parametric study on electrode distance for full-scale EKR treatment was found in this study as [Formula: see text] 0.5 m.

Comparison of different extracting agents for the recovery of Pb and Zn through electrokinetic remediation of mine tailings

This study was conducted to investigate the feasibility of Electrokinetic Remediation to remove lead and zinc from real mine tailings, collected from the Lacan's lead and zinc Mineralized Flotation Processing Plant (Markazi province, Iran). High buffering capacity, high organic matter, and heavy metal contamination were the unique characteristics of this mine tailing. Electrokinetic remediation of the mine tailings was carried out in 11 separate experiments under constant voltage gradient of 2 V/cm for 9 days. Various enhancement techniques were tested, such as 1) electrolyte conditioning using chelating agents including ethylenediaminetetraacetic acid, citric acid, acetic acid, and hydrochloric acid; 2) increasing the concentration of the catholyte solution, and 3) adding chelating agents to the soil as a pre-treatment of the tailings and the electrolyte condoning simultaneously. The concentration of each electrolyte solution was selected based on the different extraction tests that resulted in the optimal or highest extraction percentage of lead and zinc. Electrolyte conditioning, in the case of using citric acid 1 M enhanced the removal of Pb and Zn dramatically. Catholyte conditioning, using citric acid 1 M, was the most effective enhancement technique for removing Zn (38.34%); also, the best removal efficiency of Pb (51.31%) was achieved using the same electrolyte solution in both electrode chambers. Increasing the acetic acid concentration was favorable for removal of both heavy metals. Compared to catholyte conditioning, pre-treatment coupled with catholyte conditioning could not improve the removal efficiency considerably.

Aging effects on the mobility of Pb in soil: Influence on the energy requirements in electroremediation

This paper studies the possible differences in the behavior of lead as a contaminant in soil samples when it is present as "naturally-aged" for decades after the contamination, and when it has been spiked in the laboratory. This behavior differences are stablished mainly in two ways: as changes in the fractionation analysis obtained after a sequential extraction procedure (SEP) and as changes in the efficiency of the acid-enhanced electroremediation (EKR) technique. Additionally, aging effects have been studied for almost five years. In the case of the lead-spiked soil the influence of storage conditions on contaminant behavior have also been explored: 1) samples stored in capped containers at constant moisture conditions, and 2) samples in containers open to the atmosphere, with periods of water flooding and drying. Lab-spiked and the "naturally-aged" contaminants show very different behavior with respect not only to SEP analysis but also to EKR experiments. The soil spiked with a soluble lead salt presents a higher percent in the more mobile fractions. Regarding storage conditions, some changes were observed in the lead distribution along the vertical soil profile for samples stored in uncapped containers. The EKR results were also in agreement with those from fractionation analysis. Energy requirements for the remediation were estimated by a mathematical model with important differences obtained for the different soil samples. Results are indicating that it will be very unreliable to draw estimations for the "naturally-aged" soils from contaminant-spiked samples.