Recovery of rare earths and base metals from spent nickel-metal hydride batteries by sequential sulphuric acid leaching and selective precipitations

摘要

This work describes a hydrometallurgical process to recover rare earth and basemetals from spent NiMH batteries. Laboratory tests were conducted by using NiMH powders obtained in an industrial scale grinding process after a preliminary sieving (<500 μm). The most important metals present in the initial powder were nickel (29% w/w), manganese (13% w/w), zinc (8% w/w) and rare earths (lanthanum and cerium, (5% w/w); other elements were iron (1% w/w), potassium and cobalt (2.5% w/w). The results obtained showed that two sequential leaching steps were needed to dissolve almost completely lanthanum and cerium present in the samples. In the leaching experiments three parameters were studied and optimized according to a factorial experiment: sulfuric acid concentration, acid citric concentration and temperature. The average dissolution yields after the second leaching step were 100% for manganese, cobalt, zinc and rare earths and 99% for Ni. A total recovery of RE 99% was obtained after selective precipitation. Rare earths were recovered by selective precipitation with sodium hydroxide at pH less than 2 after leaching: in these conditions a precipitate composed of lanthanum and cerium sulphates are produced. A suitable flowsheet to recover RE from NiMH spent batteries with recoveries larger than 99% has been proposed.