Magnetite 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 magnetite (Fe3O4) in alkaline sodium phosphate and ammonium hydroxide solutions between 21 288°C. Measured iron solubilities were interpreted via a Fe(II)/Fe(III) ion hydroxo-, phosphato-, ammino-complexing model thermodynamic functions for these equilibria obtained from least-squares analysis data. total 14 species fitted. Complexing are reported 8 new species: Fe(OH)(HPO4)−, Fe(OH)2(HPO4)2−, Fe(OH)3(HPO4)2−, Fe(OH)(NH3)+, Fe(OH)2(PO4)3−, Fe(OH)4(HPO4)3−, Fe(OH)2(H2PO4)−, Fe(OH)3(H2PO4)3−. At elevated temperatures, hydrolysis phosphato complexing tended stabilize Fe(III) relative Fe(II), as evidenced by free energy changes fitted oxidation reactions. $$\begin{gathered} Fe(OH)_3^ - + H_2 O_ \leftarrow ^ \to Fe(OH)_4^ (1/2)H_2 (g) \hfill \\ Fe(OH)_2^{} (HPO_4 )^{2 } Fe(OH)_3 \end{gathered}$$ For temperatures below 83°C dissolved hydrogen concentration 234 μmol-kg−1, activity ferrous aqueous solution is controlled hydrous Fe(II) oxide solid phase rather than magnetite.