Sulphuric Acid Leaching of Spent Nickel Metal Hydride Car Batteries

The treatment of spent nickel metal hydride batteries (NiMHs) of Lexus vehicles to recover nickel (Ni) and cobalt (Co) as well as rare earth elements (REEs) including La, Ce, Nd and Y was investigated. Co-extraction of Al, Fe, Cr and Cu has also been examined. Following batteries’ manual dismantling to remove metallic cases, outer plastics and current collectors, the remaining parts including cathodes of black coloured nickel (oxy)hydroxides, anodes consisting of a nickel-containing alloy (AB5 mischmetal type), and separators were simultaneously ground down to −5 mm using a hammer mill equipped with sieves. The fine (−1 mm) fraction of this product was further subjected to sulphuric acid leaching to recover the high-value elements contained. Acid consumption of 14 mol H2SO4 per kg of this fraction was found to be sufficient to decrease pH to less than 1. Leaching experiments were performed using 0.5, 1 and 2 M sulphuric acid solution at 5% pulp density and temperature 50, 75 or 95 °C. The optimum conditions for the extraction of all elements were 2M H2SO4 concentration and temperature of 75 °C with the exception of Ni extraction, which reached its highest value at 95 °C and 2M H2SO4 concentration. Extractions of 93.34% of Ni, 99.03% of Co and 100% of REEs were achieved at these conditions.