Reduction roasting and bioleaching of a limonite ore.

Abstract

Two of the main challenges presented by the implementation of nickel laterites atmospheric acid leaching are: (i) high acid consumption and (ii) high final iron concentrations in the PLS. In the current work, a novel process was devised by applying pyrometallurgical and bio-hydrometallurgical operations. The experimental set-up comprised the reduction of a nickel limonitic ore with hydrogen gas in a rotary kiln, at 900 ◦C, until all the goethite was converted to metallic iron. Subsequently, the reduced sample was bioleached by mesophilic microorganisms grown on Fe2+ (Acidithiobacillus ferrooxidans) at 5% solids, 32 ◦C, and pH < 3. The results showed that an increase in the Eh values, promoted by the bacteria, resulted in the leaching Fe, Ni and Co, therefore a dissolution of 92% of the nickel and 35% of the cobalt was observed in experiments carried out with 35 Kg H2SO4/(ton of the reduced ore). The iron concentration in the liquor generated under these experimental conditions was below 5 mg/L owing to the fact that Fe3+ precipitated as jarosite. The experimental conditions applied also resulted in low acid consumption and the final total iron concentration was also reduced in the leach liquor (< 200 mg/L), which were considerably lower than the values reported for the HPAL process.