Effect of impurities on the hydrolysis of low-concentration titanyl sulfate solutions

Abstract

Hydrolysis of titanyl sulfate solutions with TiO₂ concentrations of 140–180 g/L was investigated. The effects of the concentrations of impurities present in ilmenite, for example iron(II), magnesium, and aluminium, on hydrolytic conversion, and on the morphology and composition of the hydrolysates, were examined. The results showed that with increasing impurity concentrations, the conversion was gradually decreased, but still maintained at ~95 %. The concentrations of these impurity ions substantially affected the morphology of the hydrolysates. The higher the concentrations of the impurities were, the more irregular and non-uniform were the hydrolysate particles. When iron-to-titanium dioxide (Fe/TiO₂) mass ratios in the precipitate liquors were >0.50, the hydrolysates became very compact and difficult to filter and disperse. It was found that the hydrolysate crystallites first formed primary particles which had a very similar particle sizes of 30–50 nm, despite different concentrations of titanium and the impurity ions used. The primary particles further aggregated and formed secondary aggregates probably via sulfate bridge bonds. The concentrations of the impurities substantially affected the amounts of hydrated SO₃ adsorbed by the hydrolysates, which increased with increasing impurity concentrations, resulting in increased agglomeration of the primary particles.