Recovery of neodymium from the magnets of hard disk drives using organic acids

Abstract

This work investigates the use of leaching with malic and citric acids for the recovery of neodymium (Nd) from the NdFeB permanent magnets of discarded hard disk drives (HDDs). Evaluation was made of the effect of previous roasting of NdFeB powder on the recovery of Nd. The HDDs were manually disassembled and the magnets were removed, demagnetized, and comminuted. The roasted NdFeB powder was produced by heating in a muffle furnace at 900 °C for 480 min, resulting in complete transformation of the metals into their oxides. Evaluation was made of the effects of the following leaching parameters: temperature (30–90 °C), acid concentration (0.2–1.2 M), solid:liquid ratio (1:10–1:50), and leaching time (10–900 min). For both organic acids, the best values for the first three parameters were 90 °C, 1.0 M, and 1:20. Using malic acid, the best leaching time for the unroasted NdFeB powder was 360 min, which resulted in 99% recovery of Nd. Leaching with citric acid showed good efficiency up to 60 min, with 72.8% recovery of Nd. However, for longer times, complexation between Fe and citrate led to the formation of a thick sludge, which prevented continuation of the leach. Leaching of the unroasted NdFeB powder resulted in low selectivity between Nd and Fe. In the case of the roasted NdFeB powder, the Nd recovery efficiencies achieved using malic acid and citric acid were 22% and 32.1%, respectively. However, high selectivity was obtained, with 86.0% and 98.0% Nd, relative to Fe, using malic acid and citric acid, respectively.