Mechanisms and kinetics of atmospheric acid leaching of saprolitic nickel laterite ores

Acid leaching in agitated tanks is central to hydrometallurgical processing for valuable metals’ recovery from low grade ores. This study investigates the atmospheric leaching behavior of Australian saprolitic nickel laterite ore using sulfuric acid under isothermal, batch conditions at pH 1. The primary process variables explored include time (4 h) and temperature (70 and 95 °C) on the leaching mechanisms and kinetics for -2 mm, low grade (~1 % Ni) ore dispersions at 40 wt.% solid loading. Results indicate incongruent leaching with gangue minerals alongside Ni and Co in the pregnant leach solutions (PLS). After 4 h at 95 °C, 89% Ni and 78% Co were extracted, while recoveries at 70 °C were notably lower (< 25 %). Consumption of sulfuric acid was recorded as 177 and 644 kg H2SO4/t dry ore at 70 and 95 °C, respectively. The estimated activation energy for the leaching mechanism is 79.0 ±1.0 kJ/mol. Notable differences in particle size distributions were insignificant, yet an increase in BET specific surface area of the leached product was observed. Mineralogical analyses revealed a sub-crystalline silica phase enrichment in the leached solids. The overall mechanism may be described by a chemical reaction-controlled, shrinking core model.