All-metal recovery from spent Ni-MH batteries based on electrolysis of sodium sulfate solution

Abstract

A sustainable strategy for all-metal recycling from spent nickel metal hydride (Ni-MH) batteries was proposed, where H2SO4 and NaOH solutions by the electrolysis of Na2SO4 solution were used as the leaching agent and precipitation agent, respectively. The leaching of electrode materials was performed in mild condition, and more than 99% of the rare earths were firstly precipitated at pH 1.0 in the form of double sulphates, which were converted to hydroxides by reacting with NaOH. In the following purification steps, Al3+ and Fe3+ were deposited at pH 5.5, and Zn2+ and Mn2+ were extracted by saponified D2EHPA–kerosene from the leaching solution, and two hydroxide byproducts with industrial application were obtained. Ni2+ and Co2+ were precipitated at pH 9.5 with a total recovery rate of 97.5%. The recovery efficiency of Na2SO4 was up to 97% in total. This metal recovery approach produces considerable economic profit, without solid or liquid waste in the closed-loop process.