Diverse effects of concomitant ions on copper and arsenic separation from copper electrolyte purification solutions by sulfide precipitation: thermodynamic, kinetic and mechanistic investigations

Targeted recovery of copper (Cu) from arsenic(As)-containing wastewater has been a long-standing challenge in the Cu smelting industry. Multi-stage sulfide precipitation can selectively separate Cu from Cu electrolyte purification solutions. However, the effects of concomitant ions on the separation have not been well-understood. Against this background, the sulfide precipitation behaviors of various heavy metals under acidic conditions were studied. The solubility product constant (Ksp) value of metal sulfides (Me_nS_m) and acidity significantly affect the precipitation. In the presence of Cl^-/F^-, the formation of metal–ligand complexation exhibits divergent effects on metal precipitation. Specifically, Cl^- markedly decreases the precipitation of most metals (except Cu²⁺ and As species). Conversely, F^- increases the precipitation of Bi³⁺, Cd²⁺, Fe²⁺, Ni²⁺, Co²⁺, and In³⁺, but decreases that of Sb³⁺, Sn²⁺, Cu²⁺ and As species. Thermodynamically, the formation of stable ${\text{MeCl}}_i^{n-i}$/${\text{MeF}}_i^{n-i}$ promotes the Me_nS_m dissolution and elevates the critical pH for metal precipitation. Furthermore, the competitive ability of concomitant heavy metals for H₂S follows the order: Bi³⁺ >Sb³⁺ >Cu²⁺ >As(III) > Cd²⁺ >Sn²⁺ >As(V) > In³⁺ >Zn²⁺ >Ni²⁺ >Co²⁺ >Fe²⁺. Significantly, the concomitant heavy metals in actual solutions reduce the As precipitation into Cu slags and enhance the Cu-As(V) separation. At a Cu-As(V)-Meⁿ⁺ concentration of 5–5–1 g/L, Cd²⁺ and Zn²⁺ decrease As(V) precipitation by 2.75 % and 1.47 %, respectively. Kinetically, precisely regulating the reaction time can effectively minimize the co-precipitation of As with Cu and reduce the consumption of sulfide agent. These findings have significant implications for aqueous Cu-As(V) separation and valuable metals recycling from wastewater.