Recovery of Valuable Metals in Acid-Soluble Residues from Ndfeb Waste and the Preparation of High-Purity Iron Oxide for Ferrites

Abstract

The iron contents in the acid-soluble residues from NdFeB waste are more than 50%, and the contents of rare earths and valuable metals such as cobalt are approximately 0.5%. In this study, a method for recovering valuable metals from acid-soluble residues and the preparation of high-purity iron oxide for ferrites was developed to increase comprehensive utilization of the acid-soluble residues. Firstly, the acid-soluble residue was dissolued by hydrochloric acid. After pretreatment of the leachate, a sodium sulfide solution was added to precipitate the cobalt. Precipitation enrichment with a cobalt content of 7.06% and a ferrous chloride solution with an iron proportion of 98.93% were obtained. Subsequently, the air oxidation precipition method was applied for above ferrous chloride solution to prepare a γ-FeOOH precursor. After roasting γ-FeOOH precursor at 700 °C for 2 h, an iron oxide product with a purity of 99.66% was achieved for ferrite , which met the national standard (GB/T 24244-2009). This technology can reduce the accumulation of acid-soluble residues, recover the rare earths and cobalt, and to achieve high-value utilization of iron. The comprehensive recovery efficiency for cobalt, iron, and rare earth are 91.12%,89.88%, and 85.17%, respectively, which has substantial social and economic benefits.

Keywords: NdFeB waste, recovery, high-purity iron oxide, cobalt, Rare earth