The effect of oxidant addition on ferrous iron removal from multi-element acidic sulphate solutions

Abstract

© 2017 Author(s). This study was an investigation on the hydrolytic precipitation of iron from simulated pregnant leach solution (PLS) of nickel laterite atmospheric leaching. The effect of equilibrium pH, temperature and the addition of oxidant on total iron (ferrous (Fe (II)) and ferric (Fe (III)), aluminium and chromium removal was investigated together with the associated nickel and cobalt losses to the precipitate. Systematic variations of the experimental variables revealed =99% of the ferric iron can be removed from solution at conditions similar to those used in standard partial neutralisation in zinc and nickel production, pH of 2.5 and temperature less than 100°C with minimal losses ( < 0.5%) of both nickel and cobalt. Temperature variation from 55 to 90°C had no significant effect on the magnitude of Fe (III) precipitation but led to a significant increase in aluminium removal from 67% to 95% and improved the filterability of the precipitates. There was no ferrous iron precipitation even at a pH of 3.75 in the absence of an oxidant with its removal (98%) achieved by oxidative precipitation with oxygen gas at pH 3.5. Unlike Fe (III) precipitation, the operating temperature significantly affects oxidative precipitation of Fe (II). Hence, in practical application, the hydrolytic precipitation and oxidation to remove iron must be operated at 85°C to ensure both ferrous and ferric iron are precipitated.