Desorption mechanisms of rare earths from surface of ion adsorption rare earth ores: cooperative interactions of hydrogen ions and MgSO4 revealed through batch experiments and sequential chemical extractions

The investigation of the leaching mechanisms of ion adsorption rare earth ores (IAREO) using MgSO 4 is significantly hindered by the complex mineral composition. In this study, the direct analogue of the natural IAREO sample, Y-kaolinite, was prepared and used to investigate the leaching mechanisms of rare earths from kaolinite under varying initial MgSO 4 concentrations and pH. The results of X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray absorption fine structure (XAFS) data indicate that the Y-kaolinite prepared exhibits a similar composition, micromorphology and coordination structure with nature IAREO sample. The coordination number and bond length of Y–O are 9.2±1.4 and 0.23±0.010 nm, respectively. The results of batch desorption experiments and sequential chemical extractions show that lowering the initial pH from 5.00 to 2.00 significantly enhances the desorption of rare earths from Y-kaolinite. Specifically, the additional desorption amounts are 0.52 mmol/kg for inorganic hydroxy Y (Hy-Y) and 0.40 mmol/kg for ion-exchangeable Y (Ex-Y). The enhancement mechanism was revealed by density functional theory (DFT) and Visual MINTEQ. The desorption of Hy-Y and Ex-Y is directly and indirectly enhanced by hydrogen ions, respectively. The desorption of Hy-Y is consistent with the dissolution behavior of the Y hydroxyl compound at lower pH. The desorption of Ex-Y is promoted by [Al(H 2 O) 6 ] 3+ released from Hy-Al by hydrogen ions. Additionally, when the concentration of MgSO 4 is 100 mmol/L and initial pH is 2.00, the desorption rate of rare earths is 87.1%, while the adsorption rate of magnesium is 63.1% and the stoichiometry ratio of Y 3+ to Mg 2+ is 1.04, which indicates that adequate hydrogen ions reduce the consumption of MgSO 4 and enhance the leaching of rare earth. These finding provide valuable insights into optimizing the selective leaching of rare earths from IAREO.