Mineralogical insights into anion and cation dissolution behavior in calcium arsenic residue from copper smelting: Implications for safe disposal.

This study investigates the dissolution behavior of calcium-arsenic residue (CAR) sourced from a copper smelter in China, crucial for its safe disposal. Using mineralogical analysis, we identified fine powders, medium particles, and varying crystallinity in lumps, with calcium arsenate oxides comprising 56.03 % of the total weight. Arsenic dissolution is predominantly influenced by arsenic-containing mineral phases, with calcium arsenate oxides serving as the primary controlling phase. Other cations, including copper, zinc, calcium, and lead, behave according to their respective mineral phases. At a leaching pH of 3, concentrations of heavy metal ions such as As, Zn, Cu, and Pb exceed permissible limits set by the United States Environmental Protection Agency (USEPA), reaching approximately 3500, 155, 30, and 7.5 mg/L, respectively. The release of fluoride and chloride anions remains consistent throughout the system, largely unaffected by pH variations, at approximately 10 and 200 mg/L, respectively. Additionally, the competitive interaction between SO 4 ^2- and AsO 4 ^3- for Ca²⁺ ions promote SO 4 ^2- dissolution, leading to morphological changes in gypsum (CaSO 4 ·2 H 2 O). Under acidic conditions (pH=3), there's an increase in gypsum volume, with SO 4 ^2- leaching concentration around 1100 mg/L, while under alkaline conditions (pH=12), the SO 4 ^2- leaching concentration increases to around 4400 mg/L due to the dominance of AsO 4 ^3-. Kinetic analysis suggests that arsenic release involves a combination of diffusion and interfacial mass transfer. Overall, this study provides valuable insights into the characterization and dissolution behavior of CAR-related minerals, offering comprehensive data support for their safe disposal and landfilling. [Display omitted] • CAR is formed by intersecting and mixing multiple arsenic-bearing minerals. • Lower pH promotes cation leaching and SO 4 ^2- leaching is inhibited. • Competitive precipitation of SO 4 ^2- and AsO 4 ^3- occurred during the leaching of CAR. • Mixed diffusion and interfacial mass transfer to control As leaching. [ABSTRACT FROM AUTHOR]