Optimizing microwave-assisted leaching of nickel from laterite ores: RSM-based modelling and kinetics

This study investigates the optimization and kinetics of nickel extraction from laterite ore using microwave-assisted atmospheric leaching (MAL). A Response Surface Methodology (RSM) based on Central Composite Design (CCD) was employed to evaluate the effects of leaching temperature and time, while microwave power was optimized separately. The results indicate that the optimal conditions were achieved at 90 °C, 90 min, and 264 W, yielding a nickel recovery of approximately 80%. The statistical model demonstrated good agreement with experimental data, with temperature identified as the most significant factor influencing recovery. Kinetic analysis using the shrinking-core model (SCM) revealed that the leaching process follows a mixed diffusion–reaction control mechanism, with an apparent activation energy of 75.94 kJ mol⁻1. X-ray diffraction (XRD) analysis confirmed the selective dissolution of nickel-bearing phases such as goethite and lizardite, while more stable phases, including cristobalite and hematite, remained in the residue. Compared to conventional atmospheric acid leaching (AAL), the MAL process significantly reduced leaching time while maintaining competitive recovery. These findings demonstrate that microwave-assisted leaching enhances heat and mass transfer, offering a more efficient and potentially sustainable approach for nickel extraction from laterite ores.