Kinetics of atmospheric leaching from a Brazilian nickel laterite ore allied to redox potential control

Hydrometallurgical processes are needed to extract nickel (Ni) when it is disseminated in mineral matrix. High-pressure acid leaching (HPAL) and atmospheric acid leaching (AAL) are alternatives, and AAL has the advantage of requiring mild temperatures and pressure. Reducing-reagent tests improved the extraction of metals for the specific limiting portion of the ore. Low dosage of sodium thiosulfate presented better selectivity and safer operating conditions, allowing metal extractions of 50–62 percent at 95 °C. However, the low extraction rate obtained for Ni and the similar levels of impurities — magnesium (Mg), manganese (Mn), cobalt (Co) and iron (Fe) — extracted may represent economical and technological challenges in the downstream process.