Polyacrylamide-Modified Sulfidated Nanoscale Zerovalent Iron for Arsenic-Contaminated Groundwater Remediation: Enhanced Surface Reactivity and Mobility

Modification of sulfidated nanoscale zerovalent iron (S-nZVI) with polyelectrolytes can enhance its stability, dispersibility, and mobility. In this study, anionic polyacrylamide (APAM) was used to modify S-nZVI, forming APAM-S-nZVI. The adsorbed APAM reduced nanoparticle aggregation and improved mobility in the sand columns. APAM modification altered surface sulfur species from S22– and S2– to SO42– and S2–, influencing the reactivity and fate of S-nZVI. APAM-S-nZVI removed 95% of arsenic (As) from anoxic water within 30 min, outperforming unmodified S-nZVI (84%) in batch experiments. The iron oxides on the shell of APAM-S-nZVI facilitated both the outersphere surface complexation of As(III) and its oxidation to As(V). Cleavage of long-chain APAM occurred upon its interaction with As, which was potentially driven by an oxidative scission. Column experiments revealed a higher breakthrough curve for APAM-S-nZVI (C/C0 = 90–100%) than for S-nZVI (C/C0 = 80–90%), confirming that the APAM modification improved its transport capacity in porous media. Under a continuous inflow of the 1 mg/L arsenic solution, the removal efficiency of As was greater than 80% for APAM-S-nZVI over 26 pore volumes. Consequently, polyelectrolyte modification of S-nZVI provides an effective approach for the remediation of As-contaminated groundwater.