Application of surfactant for improving leaching process of weathered crust elution-deposited rare earth ores

Weathered crust elution-deposited rare earth ores (WREOs) in China are the main source of medium and heavy rare earths in the world. In order to improve the seepage and the mass transfer of traditional ammonium salt leaching process of WREOs, surfactants were added in the ammonium sulfate leaching solution and the ammonium chloride leaching solution. The leaching kinetics, the mass transfer process, and the adhesion work and the adhesion work reduction factor calculated from the interfacial properties were studied to reveal the strengthening mechanism of surfactant. In the presence of the tested five surfactants, cetyl trimethyl ammonium bromide (CTAB), dodecyl trimethyl ammonium bromide (DTAB), sodium dodecyl sulfate (SDS), sodium oleate and oleic acid, the permeability of WREOs is improved, the rare earth (RE) leaching efficiency increase and the impurity aluminum (Al) leaching efficiency decrease, indicating its promotional effect on the leaching process of WREOs. Furthermore, CTAB shows a better leaching enhancement, and the optimal addition dosage is 0.4 g/L for the two ammonium salt leaching agent systems. The kinetics analysis shows the internal diffusion controls model of RE and Al leaching process, and the leaching kinetics equations of RE and Al related to CTAB concentration were obtained for the two ammonium salt leaching systems. According to the chromatographic plate theory, the mass transfer efficiency of RE increases with the CTAB concentration increasing until 0.4 g/L, which confirms that the optimal CTAB addition is 0.4 g/L. Smaller adhesion work and adhesion work reduction factor indicates more favorable permeation as well as the leaching process.