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 industry, acid-soluble residues are generally sent to iron and steel plants for recycling and utilization of the iron. Valuable metals such as the rare earths and cobalt in acid-soluble residues are not recovered, resulting in resource waste. 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, the leaching efficiency of iron was only 92.22% because of encapsulation by SiO2, while the leaching efficiency of cobalt, praseodymium, and neodymium were 99.64%, 99.49%, and 97.40%, respectively. After pretreatment of the leachate, a sodium sulfide solution was added to precipitate the cobalt. At this time, the precipitation efficiency for cobalt, rare earths, and iron were 91.12%, 8.52%, and 1.30%, respectively. Precipitation enrichment with a cobalt content of 7.06% and a ferrous chloride solution with an iron proportion of 98.93% were obtained. The cobalt precipitation enrichment could directly sent to a cobalt smelting plant for recycling. Subsequently, the air oxidation precipition method was applied for above ferrous chloride solution to prepare a γ-FeOOH precursor. And the content of rare earths in the filtrate obtained after iron oxidation precipitation process was 105.95 mg/L, these rare earths could be recycled and reused in the preferential dissolution process of NdFeB waste with hydrochloric acid. 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 reduces the accumulation of acid-soluble residues, effectively recovers the rare earths, cobalt, and other valuable metals, and realizes high-value utilization of the iron, which has substantial social and economic benefits.

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