Research On Comprehensive Recovery And Utilization Technology Of Secondary Waste Of NdFeB Magnets

NdFeB magnetic materials,known as"the king of permanent magnets",are a kind of permanent magnet materials with superior performance.The rare earth in its primary waste is about 30%,the boron is 1%,and the rest is mostly iron.In these elements,rare earth is a non-renewable resource,and iron has high utilization value.In this study,although the secondary waste has been recycled once,it still contains a large amount of iron and a certain amount of elements such as rare earth and cobalt.At present,there are a few reports about the secondary waste of NdFeB magnetic materials.Therefore,it is of research value and potential economic value to study the comprehensive recovery and utilization technology of secondary waste of NdFeB magnetic materials.This thesis adopted hydrochloric acid leaching method to recycle metal elements,such as iron,rare earth and cobalt.Through combining hydrolysis method and precipitation method,the iron,rare earth and cobalt in hydrochloric acid leaching liquid could be separated.The quality of the products was analyzed by chemical methods.And the phase composition,morphology,particle size of the products were characterized by instrument analysis methods.In addition,the equipment selection,economic benefit estimation and environmental protection analysis were suggested in the process of comprehensive utilization of secondary waste of NdFeB magnetic materials.The results obtained are as follows:（1）In the hydrochloric acid leaching experiment,when reaction temperature was80℃,reaction time was 5h,amount of hydrochloric acid was 102%of the theoretical amount and liquid-solid ratio of the reaction system was 4:1,the raw materials leaching rate was 96.02%,the rare earth leaching rate was 95.31%,the cobalt leaching rate was93.71%and the iron leaching rate was 93.38%.XRF and XRD analysis results showed that most metallic compounds could be leaching into the acid leaching liquid by the hydrochloric acid leaching,while some substances including silicon dioxide could not easily dissolved in hydrochloric acid to be remained in the filter cakes.（2）In iron recovery experiment,β-FeOOH was prepared by hydrolysis method.When reaction temperature was boiling point（101℃under normal atmosphere）,reaction time was 4h,Fe³⁺concentration was 0.6 mol/L and n（accelerant）/n(Fe³⁺)was2.5,the recovery of iron was 96.48%,the purity ofβ-FeOOH was 95.08%which had reached the purity requirement of iron oxide yellow class A,the retention rate of rare earth was 83.85%and the retention rate of cobalt was 94.64%.Theα-Fe₂O₃was prepared by calcining method and the calcination temperature was set by TGA result ofβ-FeOOH.When calcination time was 60min and calcination temperature was 750℃,the yield ofα-Fe₂O₃was 97.58%and the purity was 98.01%which had reached the purity requirement of iron oxide red class A.XRD and FT-IR analysis results showed that the main phases of the productsβ-FeOOH andα-Fe₂O₃were akaganeite and hematite.SEM analysis result showed that the particle ofβ-FeOOH was a rod-shaped structure with a length of about 600～700 nm and a width of about 60～70 nm,and the particle ofα-Fe₂O₃was a spherical-shaped structure with a diameter of about 200～300nm.（3）In rare earth and cobalt recovery experiments,ammonium bicarbonate was used as a precipitator.When reaction p H was 3.5～4.0,reaction temperature was 40℃,n（NH₄HCO₃）/n(RE³⁺)was 2.5 and aging time was 90min,the recovery of rare earth was94.05%,the purity of rare earth carbonate was 90.48%which had reached the purity requirement of light rare earth carbonate and the retention rate of cobalt was 97.88%.XRD analysis result showed that the main phase of the product was neodymium carbonate ochydrate.When reaction p H was 7.0～7.5,reaction temperature was 40℃,n（NH₄HCO₃）/n(Co²⁺)was 2.0 and aging time was 60min,the recovery of cobalt was95.48%and the purity of cobalt carbonate was 97.23%which had reached the purity requirement of cobalt carbonate typeⅡclass A.XRD analysis result showed that the main phase of the product was cobalt carbonate.（4）According to the economic benefit estimation,four products including iron oxide yellow,iron oxide red,rare earth carbonate and cobalt carbonate prepared from secondary waste of NdFeB magnetic materials had good economic benefits.The environmental protection analysis showed that the manufacturing process produced less industrial waste and was relatively green and clean.