Abstract:Monazite is a typical rare earth mineral resource associated with uranium and thorium. After extracting rare earth elements through existing steps such as alkaline dissolution transformation and acid preferential dissolution, the generated preferential dissolved residue is an important secondary resource rich in uranium, thorium, and rare earth. To maintain a consistent hydrochloric acid system with rare earth extraction, it is significant to study hydrochloric acid leaching process of preferential dissolved residue for the overall recovery process. A single factor experiment was conducted to investigate the effect of leaching process conditions on leaching rate of uranium, thorium, and rare earth. The results show that the leaching rate of uranium, thorium and rare earth in preferential dissolved residue can reach 90%~95%, 92%~93% and >60%, respectively under the optimization parameters including hydrochloric acid concentration of 6 mol/L, leaching time of 1.5~2 h, leaching temperature of 60 ℃, and L/S of 3 mL/g, which high resource recovery rate is achieved. The process mineralogical analysis of the leaching residue shows that it is mainly composed of gangue minerals such as zircon, thorium compounds and quartz. The remaining rare earth components are mainly concentrated in the undissolved monazite, and the rest part is a small amount of xenotime and fergusonite. The experimental results can provide basic data and useful support for the comprehensive recovery technology of monazite preferential dissolved residue.