Assessment of sulfidated nanoscale zerovalent iron for in-situ remediation of Cd-contaminated acidic groundwater near zinc smelter

Abstract

High concentrations of Cd, Zn, Ni, and Al have been detected in the soil and groundwater near Yeongpoong zinc smelter in Seokpo, South Korea. The level of groundwater pollution was significant with pH 2.6, 315.5 mg/L of Cd, 1476.0 mg/L of Zn, 249.8 mg/L of Al, and 3.2 mg/L of Ni by a long-term unauthorized discharge of wastewater. Nanoscale zerovalent iron (nZVI) has been widely used to remediate various heavy metals in groundwater, but the sulfidation of nZVI can greatly improvea the reactivity toward Cd. In this study, a sulfidated nZVI (S-nZVI) was applied to remediate groundwater near the Yeongpoong zinc smelter. The batch tests confirmed the efficient removal of Ni and Al by the S-nZVI, but especially the sulfidation greatly enhanced the selective removal of Cd (99.8%) compared to that of nZVI (7.2%). The fate of heavy metals before and after treatments was predicted by MINEQL+ modeling and particle characterization indicated that Fe in FeS on S-nZVI simultaneously displaced with Cd and Zn and formed more stable CdS and ZnS. The additional NaHCO3 injection removed the remaining Zn and Fe after the S-nZVI treatment. The sequential S-nZVI and NaHCO3 treatments in column setup with Microtox toxicity test demonstrated the applicability of S-nZVI for the remediation of real acidic groundwater contaminated by high concentrations of heavy metals.