The recovery of rare earth elements from waste electrical and electronic equipment: A review

Rare earth elements (REE) are considered critical metals due to their supply risk and growing demand in various industrial segments. Waste electrical and electronic equipment (WEEE) is a potential secondary source for recovering REE which remains unexplored on a commercial scale. Moreover, the process lacks consolidated routes, and the literature has only studied the recovery of some of the 15 REE. This systematic review describes the conditions and procedures applied to fluorescent lamps, cathode-ray tube phosphors, neodymium magnets, nickel-metal hydride batteries, printed circuit boards, LED waste, and other secondary sources to identify the challenges and gaps of recovering REE. Yttrium, neodymium, and cerium are the most commonly recovered elements. With the highest concentration of REE in its composition, NdFeB magnet residues are the most investigated as a secondary REE source. The literature highlights the use of hydrometallurgical processes to recover these elements and sulfuric acid as the most used leaching agent. The absence of studies evaluating sequential processes to recover base metals and precious and rare earth elements is well known. Note also the lack of studies investigating recovery from a mix of different residues. Additionally, to make the process more attractive to the market, researchers must conduct studies on the scale-up and economic viability of these processes.