Cobalt(II) Oxide Solubility and Phase Stability in Alkaline Media at Elevated Temperatures

摘要

A platinum-lined, flowing autoclave facility was used to investigate the solubility behavior of cobalt(II) oxide (CoO) in deoxygenated ammonium and sodium hydroxide solutions between 22 and 288 deg C. Co(II) ion activity in aqueous solution was controlled by a hydrous Co(II) oxide when nitrogen was used for deoxygenation and by metallic cobalt when hydrogen was used. Measured cobalt solubilities are interpreted using a Co(II) ion hydroxo- and amminocomplexing model and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. A common set of thermodynamic properties for the species Co(OH)~+, Co(OH)_2(aq) and Co(OH)(NH_3)~+ is provided to permit accurate cobalt oxide solubility calculations over broad ranges of temperature and alkalinity.