Insight into leaching rare earth from ion-adsorption type rare earth ores with citric acid: Performance, kinetic analysis and differentiation leaching

The rare earth elements (REEs) extraction by chemical leaching from ion-adsorption type rare earth ores (IAREO) has led to serious ecological and environmental risks. Conversely, demand of bioleaching is on the rise with the advantage of being environmental-friendly. As one of the organic acids produced by biological metabolism, citric acid was used to leach RE and explore the performance and process. The results demonstrate that citric acid exhibits higher leaching efficiency (96.00%) for REEs at relatively low concentration of 0.01 mol/L compared with (NH4)2SO4 (84.29%, 0.1 mol/L) and MgSO4 (83.99%, 0.1 mol/L). Citric acid shows a preference for leaching heavy rare earth elements, with 99% leaching efficiency in IAREO, which shows higher capacity than (NH4)2SO4 and MgSO4 (as inorganic leaching agents). Kinetic analysis indicates that the leaching process of REEs with citric acid is controlled by both the internal diffusion kinetics and chemical reaction kinetics, which is different with inorganic leaching agent. Visual Minteq calculations confirm that RE-Citrate are the main constituents of extract solution in the leaching process of the IAREO, thereby enhancing the leaching efficiency of REEs from the IAREO. It suggests that citric acid may be used as a promising organic leaching agent for the environmental-friendly extraction of REEs from IAREO.