• Journal of Soil and Groundwater Environment
• /
• v.28 no.1
• /
• pp.1-14
• /
• 2023

In this study, column tests using relatively uniform Jumunjin sand media were conducted to evaluate the feasibility of calcium polysulfide (CaS_x, CPS) in removing high concentration of Zn²⁺ in groundwater. The injected CPS solution reacted rapidly with Zn²⁺ in artificial groundwater and effectively reduced Zn²⁺ by more than 99% through metal sulfide precipitation. Since the density (d = 1.27 g/cm³ ) of CPS solution was greater than that of water, CPS solution settled down rapidly while capturing Zn²⁺ and formed stable CPS layer similar to dense nonaqueous phase liquid. Mass balance analysis on Zn²⁺ in CPS solution suggested that CPS solution effectively reacted with Zn²⁺ to form metal sulfide precipitates except for high groundwater seepage velocity of 400 cm/d. With greater groundwater seepage velocity, injected CPS did not completely dissolve at the CPS-water interface, but a partially-misible CPS layer continuously moved and reacted with Zn²⁺+ in the direction of groundwater flow. Since hydraulic conductivity (K_h) decreased slightly due to the generated metal precipitates in the inter-pores of media, injection of CPS solution should be optimized to prevent clogging. As evidenced by both XRF and SEM/EDS results, ZnS precipitates were clearly observed through the reaction between the CPS solution and Zn²⁺. Further study is warranted to evaluate the feasibility of CPS to remove high-concentration heavy metalcontaminated groundwater in complex and heterogeneous media.

• Journal of Soil and Groundwater Environment
• /
• v.29 no.5
• /
• pp.14-26
• /
• 2024

This study investigated the effectiveness of calcium polysulfide (CPS; CaS_x) injection for the in-situ immobilization of cadmium and zinc-contaminated groundwater. The research focused on the impact of CPS injection on groundwater quality parameters, such as dissolved oxygen (DO), oxidation-reduction potential (ORP), and pH, as well as heavy metal precipitate formation and aquifer's microbial community dynamics on a field scale. The results demonstrated that the injected CPS formed a reactive zone, effectively reducing cadmium and zinc concentrations for a limited period. However, contaminant rebound occurred over time, necessitating repeated CPS injections. A single injection of CPS achieved a removal efficiency of 70~99%, lasting approximately 20 days. In contrast, repeated injections sustained the removal effects up to 37 days. Chemical analyses confirmed the precipitation of cadmium and zinc sulfide (CdS and ZnS), which remained stable in the aquifer even 86 days post-injection. Elemental sulfur (S) was detected in a significant quantity, contributing to the observed low DO levels. Microbial community exhibited a shift from an initial prevalence of sulfur-oxidizing and iron-oxidizing bacteria to a later dominance of sulfate-reducing bacteria following the cessation of high DO recycled water inflow, potentially enhancing the formation of CdS and ZnS.