Hydrometallurgical Recovery Of NdFeB Magnets: Complete Leaching, Iron Removal And Electrolysis

NdFeB magnets currently dominate the magnet market. The supply risk of some rare earth metals (REM) (such as Nd and Dy) imposes an effective recovery plan for the different types and components of these magnets, while minimizing the use of chemicals and waste generation. In this study, a hydrometallurgical method was studied, which can be adjusted not only to recover REM, but also other valuable metals (such as Co, Ni and Cu) coexisting in magnets. The magnet powder is completely dissolved in dilute sulfuric acid solution to obtain more than 98% ferrous dissolved iron. Adding MnO 2 to chemically oxidize Fe ²⁺to Fe ³⁺only takes 1 hour at ambient temperature. Then, by adding Ca (OH) ₂ or MnO to adjust the pH value of the solution to more than 3, more than 99% of this ferric iron can be precipitated. However, the addition of Ca (OH) ₂ led to the formation of gypsum, and reached about. 23% of REM loss, possibly through coprecipitation into gypsum. MnO increases the concentration of Mn ²⁺solution. However, it was found that the subsequent direct electrolytic removal of Mn and Co was problematic. Low anode current efficiency (ACE) leads to high energy consumption (EC), while incomplete Mn and Co removal and undesirable REM loss are reported. The pre electrolysis removal of REM and/or Co by oxalate and/or sulfide precipitation has proved to be successful and selective, but this has greatly expanded the process, while the removal of Mn, ACE and EC have only been slightly improved.