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 3 · 2H 2O, 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 3 · 2H 2O compound occurs at 81—222 °C, and proceeds in four stages corresponding, seemingly, to formation of following intermediate hydrous compounds: ZnSeO 3 · 5/3H 2O, ZnSeO 3 · H 2O and ZnSeO 3 · 1/3H 2O. Formation of the zinc selenite in oxidation media in natural conditions seems to be possible in the stable (ZnSeO 3 · 2H 2O) or meta-stable (ZnSeO 3 · H 2O) forms. At the high temperatures (up to 479 °C) the anhydrous ZnSeO 3 compound might exist, within the range 479—597 °C it decomposes in ZnO and SeO2.