Formation of iron hydroxysulphate phases in the hematite process by hydrolysis of ferric sulphate

Abstract

Iron hydroxysulphate phases, such as hydronium jarosite and basic ferric sulphate, precipitate with hematite, which reduces the hematite quality and its potential for marketing. The factors of temperature, time, initial ferric and Zn2+ concentrations, and amount of hematite seed that have either positive or negative effects on metastable iron phase formation or conversion were studied. The temperature and initial ferric concentration have significant influence on hydronium jarosite formation in the hematite process. A large initial ferric concentration of 20 g/L can lead to the precipitation of basic ferric sulfate instead of hematite. The amounts of hematite, hydronium jarosite and basic ferric sulfate in the precipitates depend on the level of the initial ferric concentration and the presence/absence of Zn2+; purified hematite formation is favored at low initial ferric concentrations and in the presence of Zn2+. Metastable iron phases formed in the precipitation process convert to hematite to some extent with increasing temperature and reaction time.