Study On The Adsorption-desorption Behavior Of P507 Extraction Resin For Rare Earth And Non-rare Earth Impurity Ions

Ultra-high purity rare earth compounds are widely used in high-tech fields and belong to national major strategic needs.The relative purity of rare earths in existing rare earth products can reach 99.999%,however,the content of non-rare earth impurities is high,which seriously restricts the application of high-end rare earth products.The paper focuses on the existing distribution of impurity elements in rare earth feed solutions,taking La and Y as examples.the adsorption-desorption behavior of rare earths and impurities Zn,Ca,Al,Fe and Cr in chloride salt media and sulfate acid media were carried out using P507 extraction resin,respectively,and the mechanism of the adsorption process was studied by combining slope method and MS simulation calculation.The main research contents and results are as follows:（1）The physical and chemical properties of P507 resin were analyzed,and the effect of reaction time and pH on the adsorption performance of the resin was investigated by static adsorption,and the thermodynamics and kinetics of La and Y adsorption processes were also studied.The results indicate that the open pore structure of the resin facilitates the adsorption of rare earth ions and that H⁺in the phosphate functional group contained in the resin participates in the reaction.The thermodynamic parameters indicate that the adsorption is a heat absorption process that can proceed spontaneously.La and Y can reach static adsorption equilibrium after 1h,and the corresponding equilibrium adsorption capacities are 0.0989 mmol·g^-1,0.171 mmol·g^-1,respectively,the optimal pH values for adsorption of both La and Y is 4.0.The adsorption processes are in accordance with the Langmuir adsorption isotherm equation and the quasi-secondary kinetic model.（2）The adsorption-desorption laws of single rare earth and impurity ions and their mixed ions by the P507 resin in chloride salt media were investigated.The results show that the dynamic molar adsorption of single ions by the P507 resin is in the order of Zn>Fe>Y>Al>La>Ca>Cr.Taking hydrochloric acid as desorbent,with the corresponding lowest desorbent concentrations of 0.1 mol·L^-1、3 mol·L^-1、3 mol·L^-1、2.5 mol·L^-1、0.15 mol·L^-1、0.05 mol·L^-1、0.05 mol·L^-1,respectively.The resin mainly adsorb Fe and Zn in the high La stock solution,Ca and Cr are not adsorbed,the order of gradient desorption with hydrochloric acid is La≈Zn>Al>Fe.The resin mainly adsorb Fe in the high Y stock solution,and Zn,Ca,Al and Cr could be completely separated from Y,while the separation of Y and Fe is relatively difficult.（3）The adsorption-desorption law of the sulfate acid media P507 resin for rare earths and single impurity ions and their mixed ions were investigated.The results show that the dynamic molar adsorption of a single ion by the resin is lower than that of the chloride salt system in the order of Zn>Fe>Y>La>Al>Cr,where the pH value of Al,Fe,and Cr stock solution are 2.0.Taking hydrochloric acid as desorbent,the lowest acidity for complete desorption is basically the same as the chloride salt system,but the desorption acidity for Al is 3 mol·L^-1.In the high lanthanide sulfate feed solution,the resin mainly adsorb Fe and Zn,and the adsorption capacity of La is lower than that of the hydrochloric acid media,and the desorption peaks of La and Zn are close and difficult to separate.In the high yttrium sulfate feed solution,the adsorption-desorption law of impurity ions is basically the same as that of the chloride salt media,but Y and Fe are more easily separated in depth in the sulfate system.（4）A study on the adsorption-desorption mechanism of rare earth and non-rare earth impurity ions in chloride salt media,coordination and hydration law of rare earth and impurity ions were studied.The results show that for 1 mol La³⁺ion adsorbed,2mol H⁺ions are simultaneously released,and 1.5 mol for Zn²⁺ions,the adsorption process is not a simple cation exchange reaction.Increasing the acidity of the solution is beneficial for the separation of rare earths and impurity ions.In addition,MD simulation calculations show the La and Zn co-adsorption and co-desorption laws are related to the similarity of the RDF peak positions and coordination ability of H₂O molecules.