THERMODYNAMICS OF ARSENATES, SELENITES AND SULFATES IN THE OXIDATION ZONE OF SULFIDE ORES. IX. PHYSICAL-CHEMICAL CONDITIONS OF FORMATION AND THE THERMAL STABILITY OF ZINC SELENITES
Purpose of the paper is the physical-chemical analysis of formation conditions of the synthetic zinc selenite, ZnSeO <sub>3</sub> · 2H <sub>2</sub>O, and the experimental study of its thermal stability and peculiarities of its dehydration and dissociation. The study was carried out with the help of simultaneous application of the thermo-gravimetry (TG) and differential scanning calorimetry (DSC) in the range of temperatures from 25 to 600 °C. It has been revealed that dehydration of the ZnSeO <sub>3</sub> · 2H <sub>2</sub>O compound occurs at 81—222 °C, and proceeds in four stages corresponding, seemingly, to formation of following intermediate hydrous compounds: ZnSeO <sub>3</sub> · 5/3H <sub>2</sub>O, ZnSeO <sub>3</sub> · H <sub>2</sub>O and ZnSeO <sub>3</sub> · 1/3H <sub>2</sub>O. Formation of the zinc selenite in oxidation media in natural conditions seems to be possible in the stable (ZnSeO <sub>3</sub> · 2H <sub>2</sub>O) or meta-stable (ZnSeO <sub>3</sub> · H <sub>2</sub>O) forms. At the high temperatures (up to 479 °C) the anhydrous ZnSeO <sub>3</sub> compound might exist, within the range 479—597 °C it decomposes in ZnO and SeO2.