Effect of EK-PRB application on Cd ‘Focusing’ effect in soil: PRB applications, replacement of activated carbon and polarity exchange

The ‘focusing’ effect has emerged as a pivotal factor in the elimination of heavy metals from soils by electrokinetic (EK) remediation. The objective of this study was to investigate the effect of activated carbon-filled permeable reactive barrier (PRB) in combination with the EK technique on the ‘focusing’ effect in Cd-contaminated soil. To this end, five EK experiments were designed for a period of nine days by optimising the layout of PRB, periodic replacement of activated carbon and polarity exchange strategy. The results demonstrated that following a nine-day period of EK remediation, the EK3 experiment, in which the PRB was situated in front of the Cd accumulation section and the activated carbon was replaced at 4.5 days, proved effective in both mitigating and shifting the ‘focusing’ effect of Cd. Furthermore, the highest average Cd removal efficiency was observed to be 31.66%. Cd was concentrated in S3 and S5, is mainly the more hazardous exchangeable and reducible fractions. In contrast, the Cd removal rate in the areas of S1, S2, and S4 reached 70.72% to 77.07%, with the residual Cd predominantly present in the less hazardous oxidizable and residual fractions. Additionally, the EK3 demonstrated a potential for energy savings of approximately 31.88% compared to EK0. This study offers novel scientific insights into the ‘focusing’ effect of Cd during soil remediation and provides practical guidance for optimising remediation strategies for heavy metal-contaminated soils.