Leaching characteristics and kinetics of scandium from Sc-concentrate of Bayan Obo rare earth tailings in sulfuric acid solution

Abstract

Bayan Obo tailings are rich in valuable elements such as Fe, F, REEs, and Nb, which are regarded as critical secondary resources and have been studied by researchers in recent years on how to utilize them comprehensively. Among them, Sc has the highest value, but its low grade and unclear occurrence state limit its application and development. In this work, the leaching process of Sc-magnetic concentrate of Bayan Obo tailings with the grade above 500 ppm was introduced, and the effects of different leaching conditions, which consisted of stirring speed (300–500 rpm), particle size (25–75 µm), initial CH2SO4 (3–5 mol L−1) and temperature (353.15–383.15 K), on the extraction mechanism of Sc were reported. The results indicated that the leaching temperature, and initial acid concentration were positively correlated with the extraction efficiency of Sc, the mineral particle size was negatively correlated with the extraction efficiency of Sc, and the influence of stirring speed on the leaching efficiency was ignored. The dissolution order of silicate in sulfuric acid solution was biotite ˃ richterite ˃ aegirine. After 6 h of reaction, there was still a large amount of aegirine undissolved, and aegirine is one of the main Sc-riched minerals, which was the reason for the low leaching efficiency of Sc. The kinetics of the acid leaching process of Sc-magnetic concentrate under atmospheric pressure was also studied. The shrinking core model (SCM)-diffusion control-spherical particle was chosen to describe the leaching behavior of Sc, and the parameters of the kinetic equation were determined that the reaction order was 3.26 with respect to sulfuric acid with an activation energy of 54.39 kJ/mol.