Microwave Exposure of Discarded Hard Disc Drive Magnets for Recovery of Rare Earth Values

Abstract

The recovery of rare earth elements from discarded electronic waste is gaining considerable interest due to the shortage of primary resources. NdFeB permanent magnets were collected from discarded hard disc drives and consist of ~ 28% rare earth values along with 65% Fe in the form of the Nd2Fe14B phase. The magnets were demagnetized, crushed and exposed to microwave irradiation for a predetermined time. It was found that, within 1.2 min of microwave exposure, significant oxidation and a temperature of ~ 600°C was attained. Recovery from the microwave-exposed product was carried out by the leaching and precipitation route. Iron values were recovered in the form of metallic iron and iron oxide in the leach residue. The process adopted is very short and yielded 56% recovery of Nd and Dy oxides with a purity of more than 98%.