Thermodynamics of arsenates, selenites and sulfates in the oxidation zone of sulfide ores: XII. Mineral equilibria in the Cd-Se-H₂O system at 25 °C

Charykova M. V., Vishnevskiy A. V., Krivovichev V. G., Fokina E. L., Ivanova N. M., Platonova N. V., Semenova V. V.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2015. V. 144. N 5. P. 33-47

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Language: Russian

Abstract

Understanding of mechanisms of the cadmium and selenium behavior in the near-surface conditions is very important for the solving of some environmental problems. The principal aim of this study was to carry out the physico-chemical analysis of formation conditions of the synthetic cadmium selenite CdSeO3 H2O, and an experimental investigation of its thermal stability, mechanisms of dehydration and dissociation. The synthesis was realized by boiling-dry of aqueous solutions of cadmium nitrate. Obtained specimens were studied by microprobe analysis and X-ray powder diffraction method. Complex thermal analysis (thermogravimetry and differential scanning calorimetry) have shown that dehydration of CdSeO₃ · H₂O takes place at 177—241 °С in two stages corresponding, seemingly, to formation of CdSeO₃ · 2/3H₂O. Calculation and plotting of Eh-pH diagrams were realized with software GMB 9.0. Eh-pH diagrams for Cd—Se—H₂O and Cd—Se—CO₂—H₂O systems have been compiled for the average content of these elements in underground waters. Formation of the cadmium selenite (CdSeO₃ · H₂O) in oxidation media of natural conditions may be quite possible. Existence of CdSeO₃ is possible in high temperature conditions.

Key words: selenites, cadmium selenite, Eh-pH diagrams, thermogravimetry, differential scanning calorimetry.