Enhanced Percolation Leaching of Limonitic Nickel Laterite Ore Using a Combined Sulfuric–Citric Acid System

Percolation leaching of limonite Ni laterite ore (1.42% Ni, 0.07% Co, 27.16% Fe) with sulfuric acid, citric acid, and their mixture was studied at atmospheric pressure and a temperature of 25 °C. Experiments were carried out in columns (diameter 50 mm, height 500 mm, ore weight 1.5 kg) as a laboratory model of heap leaching. The combined H2SO4 + C6H8O7 system (10 + 10 g/L) showed a considerable enhancement in Ni extraction. After 21 days, Ni extraction reached 73%, compared with 52% for H2SO4 and 42% for citric acid at the same total reagent concentration. In an extended experiment (42 days), the maximum extraction of Ni reached ~83%, while that of Co was ~60%. Differences in the behavior of Ni and Co were revealed. Sulfuric acid is more effective for Ni, while citric acid is more effective for Co, due to differences in these metal species in the ore. Among the tested acid ratios, 10 + 10 g/L provided the best balance for the simultaneous extraction of Ni and Co.