Purification And Recovery Of Nd-Fe-B Sintered Sludge

In recent years,the rare earth has become an indispensable strategic resource for industrial development around the world.The demand for sintered Nd-Fe-B magnets keeps growing,and the global production increases year by year.However,a large amount of waste will be produced in the production process of Nd-Fe-B magnets,among which the sludge waste generated in the machining process accounts for about35%of the total weight of the input material.The Nd-Fe-B sludge contains a large amount of rare earth elements,which can be recovered in an efficient and economical way to mitigate rare earth supply risks and reduce environmental load.In the preliminary study on the classification of sludge waste,the Nd₂Fe₁₄B phase in slightly oxidized sludge are not destroyed,where has a lot of organic impurities and oxide impurities.The existing method usually indiscriminately remove organic impurities with high temperature which will not only lead to further oxidation of sludge but also cause the decomposition of Nd-Fe-B phase.Therefore,in this article,slightly oxidized sludge produced by oil-based slicing and multiple wire cutting are selected to explore the purification process,which is based on"physical centrifugal-organic dissolution-acid and alkali solution combination".The Nd-Fe-B powder with good dispersibility can be obtained after the purification process who can effectively remove the organic impurities and oxide impurities in the sludge.The recycled powder remains the Nd₂Fe₁₄B phase and the content of carbon,hydrogen,oxygen and other impurities is significantly reduced with good magnetic properties,which can be used in the preparation of recovery sintered magnets.In addition,it provides a new idea for the large-scale recovery of oil sludge in the future.For oil-based slicing sludge,the sludge centrifuged with cyclohexane was used as raw material.The sludge was ultrasonic cleaned by organic solution and alkaline solution of OP emulsifier,among which,acetone and 5%OP emulsifier with 10 g/L Na OH solution has a better removal effect.After ultrasonic cleaning,the carbon,hydrogen and oxygen content of the sludge was greatly reduced with the thermogravimetric curve changing,which proved that most organic impurities are removed.As a result of adjusting the concentration of OP emulsifier and HCl solution,1%OP+1%HCl solution is the best formula for oxide impurities removing.After the purification process,the carbon,hydrogen and oxygen contents of the powder decreased from 6.8 wt.%,1.8wt.%and 9.3wt.%to 0.18 wt.%,0.18 wt.%and 1.83wt.%respectively,which M_3T increased.The recovery rate of powder and the rare earth was 73.5%and 93%respectively.The sintered Nd-Fe-B magnets were prepared from the recycled powder.When doping 5%recycled powder and Nd₄Fe₁₄B powder with jet milling Nd-Fe-B powder,the sintered magnets have best magnetic properties,with the maximum magnetic energy product of 42.38 MGoe,coercivity of 13.36 k Oe and remanence of 13.28kg,respectively.For the multiple wire cutting sludge,our experiments show that the solution of5%OP emulsifier and 0.5g/L Na OH has the best effect of removing organic impurities,and the oxide impurities can be removed by the solution of 5%OP emulsifier and 2%HCl.The main phase in the recycled powder is changeless,whose dispersion and particle size distribution have been improved,with the carbon and oxygen content decreased respectively from 1.23 wt.%and 7.7 wt.%0.18 wt%and 2.2 wt.%.The hydrogen content sharply decreased to 0.07 wt.%after the removal of organic impurities but increased slightly to 0.2 wt.%due to absorbing hydrogen treating by HCl.The carbon,hydrogen and oxygen content was decreased 85%,92%and 71%respectively from the initial sludge and M_3Tincreased to 142.02 emu/g.