Study On Selective Separation And Recovery Of Rare Earths From NdFeB Magnet Scraps

The neodymium iron boron?NdFeB?magnet scraps contain valuable rare earths?RE?,which have a high comprehensive recovery value.The current treatment processes have many defects such as low recovery efficiencies of RE,complex process,large consumption of acid and alkali,and difficult utilization of iron slag.Therefore,based on clarifying the occurrence behavior of each metal of the NdFeB magnet scraps,the research of selective separation and recovery of rare earth from NdFeB magnet scraps was carried out.The main research contents are as follows:?1?The main phases of NdFeB magnet scraps are rare earth oxide and iron oxide,and the content of iron oxide is as high as 71%,which brings bigger challenge of selective extraction and separation of rare earth.?2?Based on different decomposition temperature of rare earth sulfates and other metal sulfates,roasted NdFeB magnet scraps by ammonium sulfate was proposed.The effects of ammonium sulfate amount,roasting time and roasting temperature in different roasting stages on the RE separation and recovery were studied.At the same time,the phase transformation mechanism of each roasting stage was also confirmed,and a theoretical system of selective transformation of NdFeB magnet oxides was constructed.The results show that the leaching efficiencie of RE can reach 95.80%under the conditions of mass ratio of 1:2.5?NdFeB magnet scraps to ammonium sulfate?,first stage roasting temperature of 400?,roasting time of 1 h,second stage roasting temperature of 750?and roasting time of 2 h,while the leaching efficiencies of Fe,Al,Cu and Co are only 0.0080%,0.27%,1.64%and 3.48%respectively.XRD,ICP and other characterization methods were utilized to confirm the main conversion path of rare earth sulfates in the roasting process.The conversion paths of rare earth sulfate can be explained:?1??NH₄?₂SO₄-NH₄RE?SO₄?₂-RE₂?SO₄?₃;?2??NH₄?₂SO₄-NH₄Fe?SO₄?₂-Fe₂?SO₄?₃-RE₂?SO₄?₃.?3?According to Fe₂?SO₄?₃ can cause sulfate transformation of rare earth oxides,the research on selective separation of RE from NdFeB magnet scraps by sulfate roasting based on sulfuric acid reduction was also carried out.The effects of sulfuric acid amount,roasting time and roasting temperature on separation of RE were studied.The results show that almost 98%of RE oxides are transformed to soluble rare earth sulfates with the combined action of H₂SO₄ and Fe₂?SO₄?₃ with 2.0 times theoretical amount of sulfuric acid at 750?for 2 h,while leaching of Fe,Al,Cu and Co are only0.0085%,0.43%,2.70%and 2.07%,respectively,which achieve the efficient and selective transformation and separation of RE.The amount of sulfuric acid is reduced90%compared with the reported amount of sulfuric acid required for sulfate roasting of NdFeB magnet scraps at the current stage,which not only achieves sulfuric acid reduction,but also has remarkable effect of energy saving and environmental protection.?4?The RE-rich solution obtained from water leaching was utilized to prepare rare earth oxides by oxalic acid precipitation-calcination method,sodium carbonate precipitation-calcination method,and sulfate double salt precipitation-alkali conversion-calcination method.The effects of sodium carbonate precipitation method,sodium carbonate dosage,reaction temperature,sodium carbonate concentration,feed liquid flow rate,aging time,and seed addition on REEs precipitation,particle size,and filtration performance were investigated.And the advantages and disadvantages of the three preparation methods were comprehensively compared.The results show that the RE product purity of 99.83%can be prepared by using oxalic acid precipitation-calcination method with 99.44%of higher RE yield,but the cost is also high.The sodium double sulfate precipitation-alkali conversion-calcination method has lower RE yield of 97.95%,lower RE product purity of 98.04%and higher cost,sodium carbonate precipitation-calcination method has higher RE yield of 99.12%,RE product purity of 98.33%,and lower cost,that is worthy of promotion.The research results provide theoretical and data support for promoting the green development of the NdFeB magnet scraps comprehensive recycling industry,which is of great significance.