Selective comminution for upgrading nickel and cobalt in nickel laterite ores

• Nickel is primarily concentrated in the −20 µm fraction while cobalt is more evenly distributed across the size fractions. • Adding dispersant significantly increased material throughput to the underscreen and influenced nickel and cobalt upgrading. • Selective comminution for optimizing resource utilization by enabling tailored nickel and cobalt extraction strategies. This study evaluates batch wet grinding of sized limonitic nickel laterite in a laboratory stirred mill to determine optimal conditions for nickel and cobalt upgrading. The effects of sodium hexametaphosphate (SHMP) dispersant, grinding time, and feed size fractions were investigated. The optimal grinding time for nickel upgrade was 0.1 min for −1180 + 600, −600 + 300, and −300 + 150 µm fractions using 5 % SHMP. The best results were observed in the −1180 + 600 and −600 + 300 underscreen fractions, where nickel grades increased from 0.89 % and 0.87 % to 1.18 % and 1.06 %, with enrichment ratios of 1.3 and 1.2 and recoveries of 72 % and 73 %, respectively. In contrast, cobalt was predominantly enriched in the overscreen fractions alongside Mn and Si, regardless of processing conditions. Compositing underscreen fractions resulted in a total nickel grade of 1.05 % with an enrichment ratio of 1.4, while cobalt was enriched 1.5 times in the combined overscreen with a grade of 0.25 %. Grinding an unsized feed led to only marginal Ni grade increases, emphasizing the importance of feed sizing before grinding. Implications for downstream processing were assessed, proposing two extraction strategies: (1) HPAL processing for the −150 µm fraction, with combined underscreen and overscreen materials allocated to tank leaching and heap leaching/RIMM, respectively; or (2) combining underscreen material with the −150 µm fraction (∼92 % of the total ore) for HPAL processing, while overscreen treatment route remains unchanged. Both strategies optimize resource utilization, improve process efficiency, and enhance metal recovery without material loss.