Recycling of NdFeB Magnets Using Sulfation, Selective Roasting, and Water Leaching

Abstract

NdFeB magnets currently dominate the magnet market. Supply risks of certain rare earth metals (REMs), e.g., Nd and Dy, demand efficient recycling options that are applicable to different types and compositions with minimum use of chemicals and waste generation. In this study, a hydrometallurgical method is presented, which is adjustable to all NdFeB magnets, regardless of their composition. After completely transforming powdered samples into a sulfate mixture, a suitable selective roasting and water leaching treatment resulted in 95-100 % extraction efficiencies for Nd, Dy, Pr, Gd, Tb, and Eu, while Fe remained in the resultant residue forming a marketable hematitedominated by-product. Impurities other than Fe were also greatly separated from the leachate thereby enabling the production of a liquid with at least 98 % REM purity. Such a solution then can be directly treated with subsequent shortened downstream processes without pretreatments for impurity removal. Due to decomposition reactions of impurities, including Fe, during the selective roasting stage, the majority of consumed acid is recyclable resulting in an environment-friendly flow sheet.

Recoveries of Valuable Metals from Spent Nickel Metal Hydride Vehicle Batteries via Sulfation, Selective Roasting, and Water Leaching

“…As seen in Fig. 1, the physically and chemically bonded water removal is completed around 286°C, which agrees with previous work for materials of similar composition [31,46,47]. Initial decomposition temperatures measured by TGA normally vary depending on the characteristics of the solids (particle size, shape, quantity), the sample holder, the heating rate and the composition of the gas phase [35].…”

“…Selective sulfation with SO 2 followed by water leaching has also been proposed for extraction of manganese from manganese oxide ore with high iron content [29]. Recent efforts have also been made to recover REEs from bauxite residue and from NdFeB magnets by sulfation, selective roasting, and water leaching [30,31]. The key outcome in these processes is a total dissolution of the rare earth sulfates in water, while iron, nickel, cobalt, and other elements remain in their solid oxide form.…”

“…Thermal decompositions of the Ni, Co, and REE sulfates have been studied extensively [31,[33][34][35][36][37][38]. Solubility data of different REE, Ni, and Co sulfate hydrates and stability constants for the formation of different REE, Ni, and Co sulfate complexes are available in the literature [39][40][41].…”

“…The residence time was varied from 1 to 3 h. This roasting process allowed the Ni and Co sulfate solid phases to decompose into their oxide forms while the REE remained in their sulfate forms. The temperature was selected based on available literature data on the thermal decomposition temperature range of the sulfates of REEs, nickel and cobalt [31,[33][34][35][36][37][38]45].…”

RECOVERING RARE EARTH OXIDE FROM NdFeB MAGNET OF WASTE HDDs BY LEACHING AND SELECTIVE PRECIPITATION METHODS

“…Selective crystallization experiments were carried out by the addition Na 2 SO 4 into leaching solution and filtering precipitation of complex salt after 12 -24 hours. After that, complex salt rare earth natri sulfate -ReNaSO 4 will be washed by water and added oxalic acid to create oxalate rare earth precipitation [11].…”