Removal of cadmium and zinc by calcium polysulfide in acidic groundwater: Injection ratio and precipitation mechanism

• Published in: Chemosphere (Oxford) Vol. 364; p. 143219
• Main Authors: Yoon, Sunghee, Jeong, Seulki, Moon, Changyu, Nam, Kyoungphile
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.09.2024
• Subjects: Calcium polysulfide; Groundwater; Heavy metal; In-situ remediation; Precipitation; Sulfide; Sulfide; Precipitation; Groundwater; In-situ remediation; Calcium polysulfide; Heavy metal; Heavy Metal; In-Situ Remediation; Calcium Polysulfide
• ISSN: 0045-6535; 1879-1298; 1879-1298
• DOI: 10.1016/j.chemosphere.2024.143219

In this study, we conducted lab-scale experiments to assess the applicability of calcium polysulfide (CPS) for the removal of cadmium (Cd2+) and zinc (Zn2+) from acidic groundwater, with an emphasis on the injection ratio and removal mechanism. For the experiments, CPS was used to treat Cd2⁺ and Zn2⁺ contaminated solution. Solutions were purged with nitrogen gas, and CPS was injected in an anaerobic chamber. After 18 h, solutions were filtered, and heavy metal concentrations were measured using ICP-MS and ICP-OES. Total polysulfide (Sx2⁻) concentration in CPS was determined by converting it to bisulfide (HS⁻) at pH 8.20 and quantifying via UV–Vis spectrophotometry. Precipitates were analyzed using XRD and SEM-EDS after centrifugation. The findings revealed that more than 99.5% of the heavy metals were removed when CPS/Cd2+ (w/w) = 1.45 and CPS/Zn2+ (w/w) = 2.50, determined as the injection ratios for maximum efficiency. These ratios were applicable when Cd2+ and Zn2+ coexisted. From the XRD and SEM-EDS analyses, it was clarified that Cd2+ and Zn2+ precipitated in sulfide forms, consistently showing the preferential precipitation of Cd2+ because of the lower solubility of cadmium sulfide compared to zinc sulfide. In addition, the concentration of Sx2− in the 29% CPS solution was determined to be approximately 2.442 M. Finally, by comparing the injected Sx2− concentration with the concentration of heavy metals removed accordingly, it was concluded that CPS and heavy metals react with a 1:1 M ratio. Based on the above results and precise quantification method, our study suggests that CPS can be effectively utilized to address heavy metal contamination issues and may serve as a valuable tool for the remediation and management of contaminated groundwater globally. Abbreviations: CPS, Calcium Polysulfide. [Display omitted] •Lab-scale CPS injection on the solution contaminated with Cd and Zn.•99.5% of the heavy metals were removed at the maximum efficiency injection ratio.•Cd and Zn were precipitated as sulfide by CPS in a 1:1 M ratio.•Sx2− was converted to HS− and quantified using a UV–Vis spectrophotometer.