Thermodynamics of Arsenates, Selenites, and Sulfates in the Oxidation Zone of Sulfide Ores: Part VII. Solubility of Synthetic Analogs of Erythrite and Annabergite at 25°C

摘要

Understanding the mechanisms of arsenic's behavior under near-surface conditions is one of the actual problems of contemporary mineralogy and geochemistry and is important for solving environmental problems. The aim of this study is to synthesize analogs of erythrite and annabergite and to investigate their solubility in water. These phases have been synthesized by the boiling-dry of aqueous solutions of cobalt and nickel nitrates mixed with sodium hydroarsenate alkalized with NaOH. The samples obtained have been identified with electron microprobe, X-ray diffraction, and IR spectroscopy. Solubility has been determined by the isothermal saturation method in ampoules at 25°C. The solubility has been calculated using the Geochemist's Workbench (GMB 7.0) software package. The measured solubilities of erythrite and annabergite are 10~(-35.76) and 10~(36.43), respectively. Eh—pH diagrams were calculated and plotted using the GMB 7.0 software package. The database comprises the thermodynamic parameters of 46 elements, 47 main particles, 48 redox pairs, 552 particles in solution, 624 solid phases, and 10 gases. The Eh—pH diagrams of the Ni—As— H2O and Co—As—H2O systems were plotted for the average contents of these elements in the acidic waters in the oxidation zones of sulfide deposits. The formation of erythrite and annabergite under near-surface conditions is discussed.