Enhancement of mass transfer process in column leaching by graded combination of coarse–medium–fine (C–M–F) particle packing: Application to heap leaching of ion-adsorption type rare earth ore with mixed (NH4)2SO4 and NH4Cl solution

Abstract

The heap leaching of ion-adsorption type rare earth (RE) ores confronts the problems of the poor extent of leaching and high reagent consumption. This work explored the optimization of the mass transfer process by mixed-ammonium salt leaching of RE ore samples based on the column-packing order of particle size, chromatographic plate theory, and hierarchical column leaching experiments. Furthermore, the parameters of the mass transfer process during heap leaching with the mixed-ammonium salts were optimized. Additionally, the enhancement mechanism of the mass transfer process of the preferred hierarchical ore samples was identified using the Avizo software. Results indicated that a layered and graded combination of coarse–medium–fine (C–M–F) ore samples was the best for the RE leaching effect. The optimal leaching process parameters for RE were a molar ratio of 3:1 between (NH₄)₂SO₄ and NH₄Cl, ammonium ion concentration of 0.3 mol/L, leaching temperature of 303.15–313.15 K, pH of 4–6 for the leaching agent and flow rate of 0.5 mL/min. The diffusion channels of the solute in the C–M–F samples during leaching were more even than those in the raw ore samples. Meanwhile, its average pore pressure was relatively low. The research results can provide useful theoretical references and technical support for in-situ heap leaching of RE, gold, copper and other metal elements.