Environment-friendly and selective extraction of valuable metals from saprolitic laterite via nitric acid pressure leaching: Behavior and mechanism

Abstract

Nickel laterite ore is a crucial raw resource for the development of new energy and materials sectors. In this study, an environment-friendly and economical process for saprolitic laterite was proposed using nitric acid pressure leaching technology. Firstly, the dissolution of lizardite and magnetite, oxidation of Fe²⁺, and hydrolysis of Fe³⁺ were evaluated via the thermodynamic analysis. Subsequently, the optimal leaching conditions were determined to be as follows: temperature of 150 °C, HNO₃ concentration of 349 g/L, leaching duration of 60 min, and liquid to solid ratio of 3:1 mL/g. The efficient extractions of Ni, Co, Sc, Al, Mg, and Mn were fulfilled. Notably, the hydrolysis reaction of Fe³⁺ prevented Fe leaching or assisted in Fe removal from pregnant leaching solution (PLS). The concentration of Fe in PLS was lower than 1 g/L. Furthermore, elevating leaching temperature to 230°C may reduce Al extraction. Density functional theory (DFT) calculations are conducted and reveal that the reaction between HNO₃ and lizardite includes H₃O⁺ adsorption, H₂O formation and removal, and NO₃^– adsorption. The adsorption energies of H₃O⁺, NO₃^–, and the energy barrier for H₂O removal are −5.80 eV, −2.90 eV, and 1.08 eV, respectively. Finally, the economic and environmental assessment illustrated that this process can achieve the comprehensive and green utilization of saprolitic laterite with low CO₂ emissions and holds promise for treating other acid-consuming resources.