Recovery of Rare Earth Elements from Recycled Hard Disk Drive Mixed Steel and Magnet Scrap

Recycling electronic scrap is a significant source of rare earth metals. Whereas traditional recycling routes for some electronic scrap emphasize the recovery of silver and gold, value can be attained by recovering of rare earth elements from unique feed streams. This paper describes a hydrometallurgical process for the recovery of rare earth elements from hard disk drives using HCl as a re-usable extraction medium. The mixture was selectively leached using HCl to remove the magnet alloy coating from shredded hard disk drives. The dissolved rare earth elements were precipitated using sodium sulfate, recovered as the sodium double salt, and subsequentially converted to hydroxides. The recovery of rare earth elements is consistent with amounts predicted using a thermodynamic model based on the MSE (Mixed-Solvent Electrolyte) framework of precipitated double salts. The effect of HCl concentration was measured upon the magnet dissolution rate. In addition, the leaching rates for steel were evaluated and found to be three orders of magnitude lower than the magnet alloy. An automated system was used to control leachate pH. The magnet and steel dissolution rate were examined for various HCl concentrations. The recovery of rare earth hydroxides was over 80%.