Scandium leaching behavior from Fe precipitation residues of nickel laterite HPAL processing using organic acid

Abstract

The rapid expansion of high-tech and clean energy applications has dramatically escalated the global demand for scandium (Sc), necessitating its sustainable recovery from secondary industrial waste streams. In this study, the leaching behavior, parametric optimization, and dissolution kinetics of scandium from iron–aluminum precipitation residues derived from High-Pressure Acid Leaching (HPAL) were systematically investigated. Characterization of the feedstock confirmed an iron-dominated matrix (33.93 wt% Fe, 3.39 wt% Al) containing 44.70 ppm Sc substituted within host goethite, hematite, and natrojarosite mineral phases. Lixiviant evaluation revealed that ascorbic acid achieved superior scandium extraction efficiency compared to conventional organic acids by driving the complete reductive dissolution of the host ferric matrix, albeit with substantial co-dissolution of bulk impurities. Experimental optimization demonstrated that maximum scandium extraction was achieved at 90 °C, an ascorbic acid concentration of 3 mol/L, and a solid-to-liquid ratio of 100 g/L over a 60-minute duration. Kinetic modeling across six distinct mathematical formulations established that the Zhuravlev–Lesokhin–Tempelman (ZLT) model provides the most accurate physical description of the leaching process across 30–90 °C, yielding an apparent activation energy (E_a) of 64.59 kJ/mol. This confirms that scandium extraction is governed by a chemically activated interfacial reaction coupled with three-dimensional diffusion through the porous product layer. Overall, these findings present an environmentally benign hydrometallurgical route that effectively disrupts industrial HPAL neutralization sludges to unlock critical metals for subsequent downstream separation.