Thermodynamics of arsenates, selenites, and sulfates in the oxidation zone of sulfide ores: VI. Solubility of synthetic analogs of ahlfeldite and cobaltomenite at 25°C

Abstract

The understanding of the mechanisms of the selenium behavior under near-surface conditions is an urgent problem of modern mineralogy and geochemistry, and is very important for solving environmental problems. The objective of this study is to synthesize analogs of ahlfeldite and cobaltomenite and to estimate their solubility in water. These analogs have been synthesized by mixing aqueous solutions of cobalt and nickel nitrates, respectively, and sodium selenite acidified with a solution of nitric acid. The obtained samples have been identified by X-ray diffraction and IR spectroscopy. The solubility has been determined by the isothermal saturation method in ampoules at 25°C, while the solubility products have been calculated using the Geochemist’s Workbench (GMB 7.0) software package. The solubility products of ahlfeldite and cobaltomenite are 10−9.20 and 10−9.44, respectively. The Eh-pH diagrams were calculated and plotted with the GMB 7.0 software package. The Eh-pH diagrams of the Ni-Se-H2O and Co-Se-H2O systems have been calculated for the average contents of these elements in underground water and their contents in acidic water of the oxidation zone of sulfide deposits. The formation of ahlfeldite and cobaltomenite under near-surface conditions is discussed.