Study On Recovery Of Rare Earth And Cobalt From NdFeB Waste By Natural Oxidation-ionic Liquid

In recent years,the huge consumption of global rare earth reserves has led to serious uncertainties in the supply of rare earths.Resource recycling has become one of the main solutions to this problem,and the environmental pollution problem of related waste can also be properly handled.The content of rare earth elements in NdFeB permanent magnet materials is relatively high(31%-32%).The annual consumption of rare earth elements in NdFeB permanent magnet materials accounts for more than 40% of the total annual consumption of rare earths in china,therefore,the recycling of NdFeB waste is of great significance.In order to develop a green recycling process and realize the circular economy,this paper optimizes the traditional oxidation calcination?hydrochloric acid leaching?solvent extraction process into a new process flow of natural oxidation?hydrochloric acid leaching?ionic liquid extraction in the recycling of NdFeB waste.The research work consists of the following five parts:(1)Natural oxidation by HCl-NH₄Cl mixed solution:The crushed NdFeB waste is wetted by the HCl-NH₄Cl mixed solution to realize natural oxidation without consuming energy and causing no environmental pollution.Orthogonal experiment results show that the oxidation rate of Fe can reach 94.08%after wetting with 0.7M HCl-5%NH₄Cl mixed solution and adding deionized water for 3 days,which is better than the effect of oxidation calcination.The characterization of XRD,XPS,FESEM,EDS confirmed that the phase change of the NdFeB waste experienced the oxygen absorption corrosion-hydrogen atom penetration process.(2)The leaching and neutralization of hydrochloric acid:The best neutralization condition is pH=3.6 and stand still for 3 hours.Under the optimized experimental conditions,the leaching rate of Nd is 96.8%,and the leaching rate of Fe is 39.4%.In addition,the leaching residue was characterized by FESEM and EDS,and the migration direction of B was clarified.(3)Aliquat336 ionic liquid is applied to the extraction and separation of Fe and Co:The research results show that Aliquat336 ionic liquid extracts Fe and Co by ionic complexation.Fe still has a good extraction effect when NH₄Cl is not added,while Co is not extracted when there is not enough NH₄Cl added.This difference is used to achieve the extraction and separation of Fe and Co.And the extraction experiment of Fe and Co was carried out with actual feed liquid.(4)The screening of various extraction systems and the research of the [A336][D₂EHDGAA]-[P4446][NTf₂] system for the extraction and separation of Nd:The synthesized [A336][D₂EHDGAA] was characterized by FTIR.After screening,it was determined to use [A336][D₂EHDGAA]-[P4446][NTf₂] system for the extraction of Nd,the extraction rate of Nd is 99.61%.The extraction of Nd by this system shows an ionic complex mechanism,the complexing ratio of [A336][D₂EHDGAA] and Nd is 1:3(5)Extraction and separation of Nd through the P204-[P4446][NTf₂] system:Under the best conditions,the extraction rate of Nd can reach 99.99%.The synergistic extraction effect of P204 and [P4446][NTf₂] has been researched and found that within a certain range,the extraction rate will increase when the concentration of the aqueous phase decreases.This is of great significance in the recovery and treatment of low-concentration rare earth wastewater,and the extraction system has a higher extraction rate in the HNO₃ medium.