Recycling of Rare Earth Element from Nickel Metal Hydride Battery Utilizing Supercritical Fluid Extraction

摘要

The anode of nickel metal hydride battery contains about 30 wt% of rare earth elements, namely, lanthanum, cerium, praseodymium, and neodymium. These elements are in increasing high demand, but facing supply uncertainty and near zero recycling. Current recycling practices rely on either pyrometallurgy or hydrometallurgy. The former is highly energy intensive and the latter relies on large volumes of acids and organic solvents, generating large volumes of hazardous residues. This study put the emphasis on developing an innovative and environmentally sustainable process for the urban mining of rare earth elements from nickel metal hydride battery. The developed process relies on supercritical fluid extraction utilizing CO_2 as the solvent. This process is very efficient because it runs at low temperature, and does not produce hazardous waste, while recovering about 90% of rare earth elements.