Near-Zero-Waste Approach for the Treatment of Saprolitic Nickel Laterite via a Combined Hydrometallurgical Process

Atmospheric acid leaching can be used for processing the nickel laterite ore. The lixivium composition necessitates Fe3+ separation as the first step in recovering valuable metals. However, traditional partial neutralization has the problem of significant loss of Ni2+ and Co2+ ions due to the high Fe3+ concentration. Besides, the discharged acidic residue leads to environmental pollution. This study proposes a combined hydrometallurgical method for efficiently recovering valuable components from saprolitic laterite. After atmospheric sulfuric acid leaching, the Fe3+ in the lixivium was first separated using phosphoric acid and sodium hydroxide as reagents; 92% of the Fe3+ precipitated as iron phosphate at a pH of 1.8. The charge and discharge capacities of the LFP sample prepared from this iron phosphate at the rate of 1 C were 157 and 154 mA h/g, respectively. During the recovery of Fe3+ ions, approximately 100% of other metals were retained in the aqueous solution. After adjustment of the pH to 6.0, this solution was used to remove impurities, including Al, Mn, Cr, and Fe. Then, more than 98% of Ni and Co were recovered as Ni,Co(OH)2 precipitates at a pH of 8.0–9.0. When the pH was raised to 11.0, over 98% of Mg precipitated as Mg(OH)2. The leach residue with a high silica content was used to prepare calcium silicate hydrate (C–S–H) via a hydrothermal process. The recovery of FePO4, Mg(OH)2, and C–S–H, in addition to Ni,Co(OH)2, made this a value-added process and with a near-zero residue discharge.