Applied Fundamental Research On Selective Leaching And Recovery Of Neodymium From Carbonyl Residues Of Neodymium Iron Boron

Neodymium iron boron（Nd Fe B）magnets are widely used magnetic materials.In recent years,with the development of emerging industries such as electric vehicles,electronic information,and aerospace,the demand for Nd Fe B magnets in all walks of life has increased year by year.During the manufacturing process of Nd Fe B magnets,about 30%Nd Fe B waste will be produced,and these wastes contain about 25～30%rare earth elements.Through the wet extraction process,the rare earth iron slag with lower than 0.2%of rare earth can be obtained.After iron extraction by carbonylation,the carbonylation slag with rare earth content in the range of 0.2 to 2%can be obtained.If the neodymium element in the carbonyl residue is recovered,it can bring dual benefits of economy and environment.Therefore,in this paper,a new type of ethylene glycol-maleic acid deep eutectic solvent and hydrochloric acid were used for selective leaching of Nd Fe B carbonyl slag waste.The main research results are as follows:（1）The material was first pretreated.It was dried at 100°C within 24 h,ground with the particle size below 300 mesh and roasted at 1000°C within 10h with heating rate as 5°C/min.（2）The optimal process conditions for selective leaching of deep eutectic solvents consisted of:n _EG:n _MA=2:1,T=80℃,t=5 h,n=700 rpm,S/L=1:125（g/m L）.Under these process conditions,the leaching efficiencies of neodymium and iron was 28.07%and the leaching efficiencies of iron was less than 0.01%.The P204-sulfonated kerosene system and hydrochloric acid were used to extract and strip the neodymium in the DES with the phase ratios of extraction and stripping processes as 1:1 and 2:1,respectively.The time and temperature of both the extraction and stripping processes were 20 min and25°C.Under these process conditions,the extraction and stripping efficiencies of neodymium were up to 99.35%and 98.32%,respectively.Neodymium was recovered by precipitation with oxalic acid solid powder,and the optimal process conditions for recovery consisted of solution p H as 4.0,the molar ratio of addition amount of oxalic acid to ideal addition amount of oxalic amount as1.2,T=60℃,and t=0.5 h.Under these process conditions,after two precipitation processes,the recovery efficiency of neodymium was 85.27%,and the purity of the obtained neodymium oxide was 92.58%.（3）The optimal process conditions for selective leaching of hydrochloric acid solution method consisted of the concentration of HCl as 2.5 mol/L,temperature as 60℃,leaching time as 0.5 h,stirring speed as 600 rpm,and S/L=1:2（g/m L）.Under these process conditions,the leaching efficiencies of neodymium and iron were 45.26%and 0.01%,respectively.After leaching,the neodymium in the neodymium-rich solution is directly recovered with oxalic acid solid powder,and the optimal operating conditions are:the amount of oxalic acid was 1.2 times the theoretical amount,the p H of the leaching solution was 4.0,T=60℃,and t=0.5 h.Under this process condition,after three precipitations,the recovery rate of neodymium is 96.38%,and the purity of the obtained neodymium oxide is 99.95%.