The mechanism of acid-washed zero-valent iron/activated carbon as permeable reactive barrier enhanced electrokinetic remediation of uranium-contaminated soil

[Display omitted] •The EK technology coupled with ZVI/AC-PRB technology was first applied to the remediation of uranium-contaminated soil.•The effects of the type, location and quantity of PRB on the removal of uranium from soil were studied.•The effect of AC on ZVI activity and the removal mechanism of U(VI) on mixture ZVI/AC were investigated. Zero-valent iron/activated carbon (ZVI/AC) particles can promote the reduction of U(VI) by micro-electrolysis. Therefore, they can be used to develop materials for permeable reactive barrier (PRB). In this study, citric acid (CA) mixed with ferric chloride (FeCl3) was selected as composite electrolyte, and we investigated the feasibility of electrokinetic (EK) coupled with Fe/C-PRB on the remediation of red soil artificially contaminated with U(VI). Seven EK experiments were conducted to study the effect of the type, location, and amount of PRB media on the removal of U(VI) in soil by the EK-PRB system. The results showed that the ZVI/AC mixture is superior to the single ZVI or AC as the PRB medium. For the EK-PRB system, a moderate increase in the number of PRBs and decrease in the thickness of the PRB in soil chamber can enhanced the removal of U(VI) from the contaminated soil. Under optimized conditions, after the 120 h remediation experiment obtained the maximum removal efficiency (80.58 ± 0.99%) of U(VI). Scanning electron microscopy (SEM), Energy-Dispersive X-ray Spectroscopy (EDS), infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to study the surface properties of the ZVI/AC mixture before and after the reaction. The results demonstrated that the soluble U(VI) was reduced to the insoluble U(IV) in the ZVI/AC mixture, or adsorption of activated carbon or iron corrosion products regardless of the pH distribution. This work provides a green efficient technology for the recovery of U(VI) from contaminated soil, waste slag or solid waste.