생태융합환경공학연구실

논문 초록 (Abstract)

A concentration-dependent dosing framework was developed for calcium polysulfide (CPS)-mediated immobi lization of cadmium (Cd) and zinc (Zn) in acidic, smelting-impacted groundwater. Batch experiments were conducted using three groundwater samples representing low, intermediate, and high Cd and Zn concentrations. The effects of initial metal loading on CPS demand, sulfide supersaturation, metal removal, precipitate forma tion, and immobilization stability were evaluated using geochemical interpretation, mass balance, and extraction analysis. Dosing with CPS rapidly transitioned aqueous chemistry from oxidizing to reducing, sulfide-favorable conditions. However, substantial Cd and Zn precipitation occurred only after the metal-sulfide ion activity product exceeded the solubility threshold, defining a critical CPS dosage threshold (C optimal CPS dosage (C CPS,Opt CPS,Cri ). A slightly greater ) promoted sustained precipitation and reduced metal extractability. As the initial metal concentration increased, the optimal CPS-to-metal mass ratio decreased markedly from 15.9 to 1.46 for Cd and from 5.33 to 2.47 for Zn, indicating greater CPS utilization efficiency at higher metal loadings. Solid-phase characterization by SEM-EDS, TEM-EDS, XRD, and XPS identified crystalline ZnS (s) , elemental sulfur, and Ca- bearing gypsum. Although crystalline CdS (s) was not resolved by XRD, Cd immobilization was evidenced by up to 99.7% aqueous Cd removal. Overall, the extractable metal fraction decreased with increasing initial metal concentration, indicating that immobilization stability depended on both CPS stoichiometry and supersaturation- controlled nucleation and precipitate growth. These findings demonstrate that CPS dosage should be based on both metal loading and site-specific geochemical demand rather than only stoichiometric sulfide requirements.