Microwave-assisted organic-acid leaching of major and critical elements from olivine: Characteristics, kinetics, and method comparison
Sepehr Ghaderi, Wencai Zhang
Abstract
Olivine has become a promising source of Ni and Co for catering to the increased global demand for critical minerals in recent years. The performance of microwave-assisted leaching of major elements, including Mg, Si, Fe, and critical elements like Co and Ni, from olivine was compared with those of autoclave and conventional leaching methods in an organic acid medium. In addition, the effects of organic acid type, citric acid concentration, solid-to-liquid (S/L) ratio, reaction time, and reaction temperature were investigated using the response surface methodology with central composite design. Accordingly, the optimal conditions were determined as 0.84 M citric acid concentration, 2.6% S/L ratio, 29 min, and 178°C. Compared with autoclave and conventional leaching techniques, microwave-assisted leaching resulted in a higher extraction of major and critical elements. The Avrami model was applied to fit the microwave-assisted leaching kinetics data and derive the kinetic parameters. The apparent activation energy values indicated that the microwave-assisted leaching process was diffusion-controlled. The characterization of solid residues resulting from the microwave-assisted leaching experiments indicated that the detachment of Si-rich layers from the surface of unreacted olivine particles during the reaction was the key factor enabling a greater degree of extraction, whereas Si-rich layers surrounded the unreacted olivine particles in the autoclave leaching method. This study provides valuable insights into the leaching characteristics and kinetics of the major and critical elements from olivine using microwave-assisted leaching in organic acid media. In addition, investigating the leaching of major elements is necessary because Ni and Co are well distributed in the olivine silicate structure. Leachates containing major elements can also be used for carbon fixation.