Abstract
The passivation and clogging of reactive media critically limit the long-term efficacy of zero-valent iron (ZVI)-based permeable reactive barriers (PRBs) for in-situ groundwater remediation. To overcome this limitation, this study proposes a novel in-situ regeneration method employing a citric acid (CA) and ascorbic acid (AA) to restore the Cr(VI) removal capacity of a deactivated biochar-supported nanoscale ZVI (BC-nZVI) PRB. Results show that the optimal regeneration efficiency was achieved with a 2.5 g/L regenerant concentration for 1 h, yielding regeneration rates of 101.7% for citric acid (CA) and 79.7% for ascorbic acid (AA), respectively. After regeneration, the BC-nZVI exhibits enhanced pH tolerance for Cr(VI) removal compared to the pristine BC-nZVI. Notably, AA-treated systems demonstrate superior recyclability, maintaining high removal efficiency over multiple cycles, whereas CA-treated systems show only moderate regeneration performance. Mechanistically, CA provides rapid initial kinetics by promoting the dissolution of the iron passivation layer through complexation, while AA favors a solid-surface reduction pathway that better preserves material stability. Moreover, the regeneration process can effectively control the mobility of chromium, and through the combined actions of reduction, complexation, and co-precipitation, Cr(III) in the aqueous phase can be ultimately restored to baseline levels.This work provides a viable, low-cost, and environmentally friendly strategy to drastically prolong PRB lifespan, circumventing the need for expensive media replacement and offering a sustainable solution for long-term site remediation.
[Display omitted]
•A chemical regeneration strategy was developed for deactivated BC-nZVI.•Reactivity recovery was governed by three synergistic mechanisms.•Citric acid exposed reactive iron cores via ligand-mediated crust dissolution.•Ascorbic acid sustained long-term reactivity through surface-mediated reduction.