Effect of roasting activation of rare earth molten salt slag on extraction of rare earth, lithium and fluorine

Abstract

A new process was proposed to extract rare earth elements (REEs), Li and F from electrolytic slag of rare earth molten salt by synergistic roasting and acid leaching. Firstly, the thermodynamic analysis of roasting reaction was carried out, then the effects of roasting factors on leaching REEs, Li and F in slag were investigated. In additions, the mineral phase and morphology of molten salt slag, roasting slag and acid leaching slag were characterized, and the migration mechanism of REES, Li and F minerals in roasting and leaching process was analyzed. The results show that the synergistic roasting and activation of molten salt slag by CaO and Al2(SO4)3 are thermodynamically feasible. The optimum roasting conditions are as follows: molten salt slag of 20 g, Al2(SO4)3 of 31.25 g and CaO of 6.25 g, roasting temperature of 1173.15 K and reaction time of 2 h, under this condition, the leaching rates of Nd, Pr, Gd, Li and F are 92.47%, 91.56%, 91.08%, 96.69% and 96.8%, respectively. X-ray powder diffraction (XRD) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) analysis show that the rare earth fluoride (REF3) in molten salt slag transforms into soluble rare earth oxide (REO) after roasting and activation. After leaching, the leaching residue is mainly strip CaSO4, indicating that REES, Li and F can be fully extracted from molten salt slag.