Direct leaching of coarse nickel laterite: reducing grinding energy consumption

초록

Nickel laterite ores are generally classified by size before leaching, and coarse fractions are either subjected to comminution, despite the high energy demand of grinding, or excluded from processing. To evaluate the feasibility of leaching coarse particles without additional comminution, Philippine saprock and limonite ores were classified into coarse, intermediate, and fine fractions to investigate the effect of particle size on the behavior of atmospheric acid leaching of nickel, iron, and magnesium. The nickel leaching efficiencies of the coarse fractions were 68.7% for saprock and 58.4% for limonite, showing comparable final values to those of the corresponding fine fractions when the heterogeneity of the coarse ores was considered. The behavior was attributed to penetration of the lixiviant into the particle interior through micropores and microcracks present within the coarse ore. Grinding the ore to a D90 of less than 150 μm required energy inputs of 7.59 and 5.69 kWh/t-ore for saprock and limonite, respectively. However, the nickel leaching efficiencies after grinding were 71.6% for saprock and 56.6% for limonite, indicating that additional comminution provided limited improvement in nickel extraction. Process-relevant indicators further showed that the coarse fractions had relatively high Mg/Ni ratios, suggesting that magnesium co-dissolution should be considered in downstream process design. These findings demonstrate that direct leaching of coarse laterite ore can achieve significant nickel recovery while reducing the energy consumption associated with additional grinding.

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