Effect of particle size on the leaching of a weathered crust elution-deposited rare earth ore

Weathered crust elution-deposited rare earth ore is a typical porous medium, and the size of ore particles plays a crucial role in solution flow and rare earth ion transport. Ore particles with different sizes were obtained, and column leaching experiments were performed to study their seepage and leaching characteristics. Subsequently, the mechanisms underlying the effect of particle size on leaching were analysed. The results showed that the maximum concentration of the rare earth leachate and the penetration time of the samples decreased with the increase of the ore particle size, and the flow rate of the leachate exhibited an opposite trend. The breakthrough curves of the samples exhibited two forms: monotonically decreasing and parabolic. When the leaching solution was sufficient, the leaching efficiencies of the samples comprising ore particles larger than 5 mm and smaller than 0.075 mm were 75% and 95%, respectively, whereas the leaching efficiencies of the other samples reached 100%. The influencing mechanism showed that when ore particles are large, the pores among the particles lead to a low leaching efficiency. On the contrary, when the ore particles are small, the re-adsorption of rare earth ions to the surface of the ore particles can be easily promoted under the combined action of poor permeability, the high clay mineral content, the large specific surface area, the imbalance of the salt solution concentration between the ore and the solution and the weakly acidic leaching environment, resulting in a low leaching efficiency. Furthermore, the micromorphology of ore particles with a small size showed a rough surface, and the structure destroyed by leaching was unconducive to the flow rate of the solution in the orebody.