Thermodynamics of arsenates,selenites, and sulfates in the oxidation zone of sulfide ores: I. Thermodynamic constants at ambient conditions

Understanding and deciphering processes proceeding near the surface are among the urgent tasks of contemporary mineralogy and geochemistry, which are especially important for resolving ecological challenges and developing principles of rational environmental management. The paper presents systematized data published on thermodynamics of minerals (arsenates, sulfates, selenites, and selenates), which are formed in the weathering zone of sulfide ores, and determines approaches to quantitative physicochemical modeling of their formation conditions. Diagrams of phase and chemical equilibria (Eh-pH, diagrams of solubility) of the subsystems of the model system Fe-Cu-Zn-Pb-Co-Ni-As-Se-S-H₂O (Fe²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Pb²⁺, Ni²⁺, Co²⁺, H⁺//SeO₃²⁻, SeO₄²⁻, AsO₄³⁻, SO₄²⁻, OH⁻-H₂O) are used as a thermodynamic basis for modeling mineral-forming processes in the weathering zone of ore deposits. Seventy-two arsenates, about 70 sulfates, and 7 selenites and selenates have been identified in the framework of this system. The available published values of standard thermodynamic functions of the formation of minerals and chemical compounds are given, as well as the Pitzer equation parameters to describe the sulfate systems, which are substantially specific due to the high solubility of their components.