Lanthanide Separation Using Size-selective Crystallization Of Ln-MOFs

Rare earth materials have a broad market and play an important role in strategic owing to their excellent light,electricity,magnetic,catalytic,superconductivity and other functions.However,the development of rare earth industry is limited by the coexistence of rare earth resources in nature.And traditional lanthanide separation methods couldn't meet the requirements of industrial production because of their high cost,low efficiency,long cycle,large environmental pollution and so on.Thus a new approach of lanthanide separation is urgently needed in order to promote the rare earth industry to grow healthy and orderly.In this thesis,olsalazine sodium was used as the organic ligand,and the trivalent rare earth ions Ln?III?were viewed as metal centers.13 kinds of metal organic frameworks?MOFs?were obtained by using olsalazine sodium and trivalent rare earth ions Ln?III?through hydrothermal reaction.Note that these 13 Ln-MOFs present four types of different structures,and were divided into four types successfully.Based on this,we designed additional experiments with mixed metals in order to further explore their ability of separation.This thesis is mainly composed of five parts.?1?Three Ln-MOFs were synthesized with the ligand olsalazine sodium and La?III?,Ce?III?,Pr?III?by solvothermal method.The MOFs formed by La?III?,Ce?III?,Pr?III?have the same unit cell parameters,named Ln-1-MOFs.?2?Three Ln-MOFs were synthesized by olsalazine sodium and Nd?III?,Sm?III?,Eu?III?.As they share the same unit cell parameters with each other,thus they were called Ln-2-MOFs.?3?Four Ln-MOFs were synthesized by using olsalazine sodium and Gd?III?,Tb?III?,Dy?III?,Ho?III?through solvothermal method.The MOFs constituted by Gd?III?,Tb?III?,Dy?III?,Ho?III?with the same unit cell parameters,named Ln-3-MOFs.?4?Three MOFs contain Er?III?,Tm?III?,Lu?III?was formed with olsalazine sodiumby solvothermal method.As a same structure they present,they all belong to Ln-4-MOFs.?5?What matters for Ln³⁺ separation is the extent and effectiveness.We designed six sets of parallel experiments to further explore the degree of separation.Firstly,we chose a metal from Ln-1-MOFs,Ln-2-MOFs,Ln-3-MOFs and Ln-4-MOFs respectively.Then,we used two metals mixed together with a molar ratio of 1: 1 instead the single metal in the initial experiments,and made olsalazine sodium reduced to half of the original.And found that only MOFs consisted of smaller Ln³⁺ existing.On this basis,we added 0.005 mmol olsalazine sodium to reactor,and made three metals mixed together with a molar ratio of 1: 1: 1 replaced the single metal in the solvothermal reaction.The resulting MOFs only present the structures made up of smaller metal.Moreover,four metals mixed together with a molar ratio of 1: 1: 1: 1 was displaced the single metal,while a quarter of olsalazine sodium were used in the experiments,at last only one structure with the smallest metal synthetized.From which we found that the smaller Ln³⁺ ion is preferred for a given MOF in the mixed metals,so as to achieve the purpose of separation.It also reflects that "lanthanide shrinkage made the length of Ln³⁺ radius shorter and shorter,rare earth complex more and more stable".