A discussion on the leaching process of the ion-adsorption type rare earth ore with the electrical double layer model

The practice of in-situ leaching of the ion-adsorption type rare earth ore using (NH4)2SO4 had revealed serious ammonia-nitrogen pollution. Therefore, a discussion on the leaching process of the ion-adsorption type rare earth ore with the electrical double layer model was presented in this paper, so as to screen out the green and efficient leaching agent and the appropriate leaching measures to improve the rare earth leaching efficiency and reduce or even eliminate ammonia-nitrogen emissions. It was determined that the leaching process could be described as the formation of a new stable electric double layer (EDL). The potential φ(x) with the distance x from clay surface to bulk solution in the diffusion layer was obtained, it showed that the potential φ(x) would decrease with the increase of the cationic charge of leaching agent, the leaching temperature and the concentration of leaching agent, leading to a higher rare earth leaching efficiency. The theoretical analysis was verified by soak leaching experiments. The results showed that the law of rare earth leaching efficiency was in agreement with the theoretical analysis. And the rare earths partition in the leaching liquor under different conditions was substantially constant except cerium element. Therefore, the cation and anion of leaching agent should have a large electric density and be environmental friendly, of which magnesium sulfate could be preferred. Moreover, chemical substances, which could form a more stable coordination with rare earth ions, could be used as an assistant to promote the leaching equilibrium to move toward a favorable direction. This paper had provided a theoretical foundation and application basis for the leaching of rare earth from the ion-adsorption type rare earth ore, and show the direction on reducing or even eliminate ammonia-nitrogen emissions.