The effect of ozone on the removal of ferrous iron from zinc sulphate solution by oxidative precipitation

Abstract

ABSTRACT Iron is a harmful constituent in zinc hydrometallurgy solution owing to the negative effects on the current efficiency and the quality of cathode zinc, and should be deeply removed before zinc electrowinning. The thermodynamics and kinetics for ozone precipitation of Fe2+ from ZnSO4 solution is presented. In thermodynamics the Gibbs free energy for possible precipitation reactions is calculated, and the potential-pH diagrams for Fe–H2O and Zn–H2O systems are presented. The results show that the oxidation of Fe2+ using O3 to form FeOOH at 298∼373 K prevails spontaneously. Meanwhile, the effect of O3 flow rate (Qozone) on the kinetics of Fe removal and the performance of precipitates is studied. The reaction fits better on the pseudo-first order kinetics and follows a 1.899 order rate with respect to Qozone. The rate constant kobs increases from 0.0084 to 0.045 min−1 with Qozone increasing from 4.08 to 10.3 g/h. The obtained precipitates are comprised of FeOOH and ZnSO4·H2O, and have good filterability. Ozonation precipitation can be used as an efficient method for deep removal of Fe.