Self-driven and efficient leaching of limonitic laterite with phosphoric acid

Abstract

With the rapid development of electric vehicles, the demand for nickel and cobalt as ternary cathode materials has increased. High-pressure acid leaching is a typical process employed for extracting nickel and cobalt from limonitic laterite. Because of the high iron content, this process requires a high temperature and pressure (245–255 °C, 4.3–4.8 MPa) for precipitation of dissolved Fe, not to mention the massive acidic residue discharge. This paper proposes a moderate and effective leaching method using phosphoric acid as the reagent for treating limonitic laterite. Based on the differences in the solubility of phosphates, the dissolved Fe3+ reacted with the ionized PO43- to form iron phosphate during leaching, whereas the dissolved Ni2+ and Co2+ remained in the solution, thus realizing the selective leaching of Ni/Co over Fe. The decrease in the real-time amounts of Fe3+ and PO43- in the solution through precipitation promoted goethite dissolution and H3PO4 dissociation, respectively, which in turn facilitated the formation of iron phosphate. In this stage, the Ni2+ doped in the goethite was released steadily. The percentages of Ni, Co, and Fe leaching were 99.2, 81.8 and 0.54%, respectively, in a 3 mol/L H3PO4 liquor at 130 °C for 2 h. Compared with high-pressure leaching, the temperature required was decreased by 115–125 °C, and the hydrothermal pressure was only 0.2–0.27 MPa. Furthermore, because of the synchronous precipitations of Fe3+ and Al3+, a lamellar Al-doped iron phosphate was obtained at a (Fe + Al)/P molar ratio of 1.0, with a near-zero residue discharge.