Decomposition of mixed rare earth concentrate by NaOH roasting and kinetics of hydrochloric acid leaching process

A new clean extraction technology for the decomposition of Bayan Obo mixed rare earth concentrate by NaOH roasting is proposed. The process mainly includes NaOH roasting to decompose rare earth concentrate and HCl leaching roasted ore. The effects of roasting temperature, roasting time, NaOH addition amount on the extraction of rare earth and factors such as HCl concentration, liquid-solid ratio, leaching temperature and leaching time on the dissolution kinetics of roasted ore were studied. The experimental results show that when the roasting temperature is 550 °C and the roasting time is 60 min, the mass ratio of NaOH:rare earth concentrate is 0.60:1, the concentration of HCl is 6.0 mol/L, the ratio of liquid to solid (L/S) 6.0:1.0, and the leaching temperature 90 °C, leaching time 45 min, stirring speed 200 r/min, and the extraction of rare earth can reach 92.5%. The relevant experimental data show that the process of HCl leaching roasted ore conforms to the shrinking core model, but the control mechanism of the chemical reaction process is different when the leaching temperature is different. When the leaching temperature is between 40 and 70 °C, the chemical reaction process is controlled by the diffusion of the product through the residual layer of the inert material. The average surface activation energy of the rare earth element is E_a = 9.96 kJ/mol. When the leaching temperature is 75–90 °C, the chemical reaction process is controlled by the interface transfer across the product layer (product layer interface mass transfer) and diffusion. The average surface activation energy of rare earth elements is E_a = 41.65 kJ/mol. The results of this study have certain significance for the green extraction of mixed rare earth ore.