From Mineralogy to Process Design: The Role of Particle Size Distribution on Nickel Extraction Kinetics and Hydrometallurgical Route Selection in a Limonitic Laterite

The mineralogical distribution of nickel within lateritic ores plays a fundamental role in leaching performance and process selection. This study investigated the influence of particle size on mineralogy, leaching kinetics, and nickel extraction using a limonitic nickel laterite from Northeastern Brazil. The ore was separated into coarse (>100#) and fine (<100#) fractions and characterized by chemical and mineralogical analyses. The coarse fraction was enriched in serpentine, vermiculite, and a poorly crystalline Fe–Si phase, whereas the fine fraction was dominated by iron oxyhydroxides (goethite–limonite). Atmospheric sulfuric acid leaching tests were performed at 95–99°C for 7 h using 600 g of ore, 600 g of H₂SO₄, and 1800 g of water. Process variables, including pH, redox potential, free acidity, liquor density, and elemental concentrations, were monitored throughout the experiments. Nickel extraction reached approximately 95% in both fractions; however, marked differences in dissolution kinetics were observed. The coarse fraction exhibited faster initial nickel extraction due to the rapid dissolution of nickel-bearing phyllosilicates and Mg-rich phases, while the fine fraction displayed slower kinetics associated with the progressive dissolution of goethitic iron phases. Correlations between Ni, Fe, and Mg extraction demonstrated the strong mineralogical control of metal release. Kinetic modeling indicated distinct rate-controlling mechanisms between granulometric fractions. The results suggest that nickel associated with phyllosilicates and poorly crystalline Fe–Si phases can be efficiently recovered by atmospheric leaching, whereas nickel hosted in iron oxyhydroxides may be more suitable for high-pressure acid leaching (HPAL). A geometallurgical processing strategy based on particle-size classification is proposed to optimize route selection and improve overall process efficiency.