Abstract
A platinum-lined, flowing autoclave facility was used to investigate the solubility behavior of nickel(II) oxide (NiO) in deoxygenated ammonium and sodium hydroxide solutions, between 21 and 315°C. Solubilities were found to vary between 0.4 and 400 nmol-kg−1. The measured nickel ion solubilities were interpreted via a Ni(II) ion hydroxo- and ammino-complexing model, and thermodynamic functions for these equilibria were obtained from a least-squares analysis of the data. Two solid phase transformations were observed: at temperatures below 149°C, the activity of Ni(II) ions in aqueous solution was controlled by a hydrous Ni(II) oxide (theophrastite) solid phase rather than by anhydrous NiO (bunsenite); above 247°C, Ni(II) activities were controlled by cubic rather than by rhombohedral bunsenite.
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Ziemniak, S.E., Goyette, M.A. Nickel(II) Oxide Solubility and Phase Stability in High Temperature Aqueous Solutions. Journal of Solution Chemistry 33, 1135–1159 (2004). https://doi.org/10.1023/B:JOSL.0000048061.87789.81
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DOI: https://doi.org/10.1023/B:JOSL.0000048061.87789.81