Thermodynamics of arsenates, selenites and sulfates in theoxidation zone of sulfide ores

Clzarykova M. V., Krivovichev V. G.

Thermodynamics of arsenates, selenites and sulfates in theoxidation zone of sulfide ores. XIII. Calculation of the Gibbs energy of formation for syntheticanalogues of cobaltomenite, alpheldite and chalcomenite on the base of their solubility in water

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 5. P. 110-117

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Language: Russian

Abstract

Understanding mechanisms of selenium’s behavior in the near-surface conditions is an actual problem of the modern mineralogy and geochemistry, and it is very important for solving some environmental challenges. The aim of the present work is to define the Gibbs energy of formation (∆_fG⁰) for synthetic analogues of three minerals: cobaltomenite (CoSeO₃2H₂O), alpheldite (NiSeO₃2H₂O) and chalcomenite (CuSeO₃2H₂O) on the base of their solubility in water. Solubility was determined by the isothermal saturation method in ampoules at temperature 25 °C. Calculations of ions’ activities in the solution in equilibrium with solid phases were spent by means of the software package Geochemist’s Workbench (GMB 9.0). It has been revealed that dissolution of cobaltomenite, alpheldite and chalcomenite is the incongruent one and accompanied by formation of Co, Ni and hydroxides. Detected ∆_fG⁰ values are: CoSeO₃2H₂O = –937.5 kJ/mol, NiSeO₃2H₂O = –931.3 kJ/mol, and CuSeO₃2H₂O = –836.3 kJ/mol. These data are well corresponding to the ∆_fG⁰ values obtained by calorimetric investigations of thermodynamic characteristics of synthetic analogs of cobaltomenite, ahlfeldite and chalcomenite.

Key words: thermodynamics, selenites, alpheldite, cobaltomenite, chalcomenite, solubility products, incongruent dissolution.