Recovery Of Rare Earth And Iron From Ultrafine NdFeB Waste By Hydrometallurgy And Electrodeposition

This paper proposed a simple and sustainable process to recover rare earths and iron from the ultrafine powder.This is very important for the sustainable development of rare earth resources.Firstly,the difference between the magnetic susceptibility of rare-earth hydroxide and iron oxide was used to separate them by magnetic separation.However,the separation cannot be performed due to the close combination of their interface.Secondly,iron oxide in the ultrafine powder was reduced by carbon at 1,100,1200,1300,and 1400℃.Rare-earth hydroxide in the ultrafine powder was converted into rare-earth oxide,and iron oxide was converted into metallic iron by the result of XRD.However,their separation was not still achieved by magnetic separation.It was found by SEM observation that the interface between the rare-earth oxide and iron was very tight.Therefore,it was suggested that it is difficult to separate rare-earth elements and iron in ultrafine powder by magnetic separation.In this work,hydrometallurgy and electrodeposition techniques were further employed to recover rare earth and iron from ultrafine powders.The rare earth and iron in the ultrafine powder were quickly separated by only one-step selective reaction of hydrofluoric acid with rare-earth hydroxide.The rare earth hydroxide was converted into rare-earth fluoride as precipitate,and iron oxide was dissolved in the hydrofluoric acid.The recovery rate of the rare earth finally reached 99.89%.Iron was recovered from the leachate by electrodeposition,and the effect of pH on iron reduction reaction was analyzed by thermodynamic software.Different reduction products can be obtained at cathode by controlling the pH of leachate.When the pH of leachate was 2.3 and2.89,the deposits were obtained for dendritic nano-FeF₂ and spherical nano-iron,respectively.The reduction reaction of Fe（III）/Fe was studied by cyclic voltammetry,chronopotentiometry and open-circuit chronopotentiometry.The reduction reaction was quasi-reversible,and the process was controlled by diffusion.The relationship between diffusion coefficient and temperature was established lnD=-9.84-1805.43/T.The diffusion activation energy was calculated to be 15.01 kJ mol^-1.The relationship between Gibbs energy of formation of Fe-Pt intermetallic compound and temperature was established asΔG=-487.53+0.936T.The used hydrofluoric acid solution can still be used to leach the ultrafine powder,realizing the sustainable utilization of the hydrofluoric acid.There is no waste and pollutant emission in the process,achieving the sustainable recovery and zero waste emission.