Remediating zinc-contaminated groundwater with calcium polysulfide using model porous media and simulated groundwater

This study demonstrates the feasibility of using calcium polysulfide (CPS) for in-situ redox manipulation (CPS-ISRM) to remediate Zn-contaminated groundwater, focusing on concentrations exceeding 10,000 mg/L at a zinc smelting site in South Korea. Experiments with sand-only and sand-clay columns revealed that subsurface heterogeneity significantly impacts CPS transport, reactivity, and removal efficiency. Homogeneous sand conditions allowed rapid CPS migration and over 99 % Zn removal, albeit within a shorter reactive time frame. In contrast, heterogeneous sand-clay media enabled prolonged localized reactions due to CPS retention, although with less than 50 % Zn removal due to restricted distribution. CPS interactions with groundwater and geochemical constituents varied based on subsurface conditions, influencing permeability and chemical evolution. Precipitation including the formation of ZnS_(s) and CaSO_4(s) drove localized clogging and changes in hydraulic conductivity, particularly in confined zones of the sand-clay column. These findings highlight the importance of subsurface characterization and tailored CPS injection protocols, considering site-specific factors such as subsurface heterogeneity, groundwater chemistry, and interactions between CPS, groundwater constituents, and the targeted contaminants. Understanding these system dynamics is imperative for optimizing CPS-ISRM technology for field-scale groundwater remediation.