A cleaner and sustainable method for recovering rare earth and cobalt from NdFeB leaching residues

NdFeB leaching residues (NLRs) is produced by the treatment of NdFeB waste by HCl preferential dissolution method, which contains about 1% rare earth and cobalt (Co). The extraction of valuable elements from the residue has a great impact on the sustainable utilization of rare-earth resources. In this study, a high-efficiency hydrometallurgy process was proposed to achieve a high conversion of valuable elements and the recycling of additives by reductive acid leaching. First, NLRs were characterized by the Bgrimm process mineralogy analyzing system, which confirmed that the iron oxide main phase encapsulates the rare earth phase. It was effective in destroying the main phase by chemical dissociation. In addition, the effects of temperature, reaction time, initial acid concentration, solid-liquid ratio (S/L), and reducing agent dosage on leaching efficiency were investigated. Under optimal conditions, 90.6% Co, 89.1% neodymium (Nd), 77.2% praseodymium (Pr), 88.7% cerium (Ce) and 83.8% iron (Fe) leached. The reaction mechanism and leaching kinetics in the leaching process were systematically explored. The kinetic analysis indicated the leaching reaction of Co and Fe was controlled by interfacial chemical reaction and the leaching reaction of Nd, Pr and Ce was controlled by internal diffusion. The activation energies of Co, Fe, Nd, Pr and Ce were 21.06, 18.07, 23.37, 20.56 and 18.52 kJ/mol. Furthermore, the reducing agent (copper powder) was successfully recovered by iron powder. The recovery rate of the copper powder was 99.93% and the purity was 93.42%. The proposed process has a promising application for industrialscale recycling.