Development of a Hydrometallurgical Process for the Recovery of Valuable Metals from Synthetic Sulfuric Acid Leaching Solution of Ni-MH Batteries

Nickel-metal hydride (Ni-MH) batteries contain valuable metals such as cobalt, nickel, and rare earth elements (REEs). Considering the demand for these metals, it is important to develop an efficient process for the recovery of valuable metals from spent Ni-MH batteries. In this work, synthetic sulfuric acid leaching solutions of spent Ni-MH batteries containing Co(II), Fe(III), Mn(II), Ni(II), Zn(II), Ce(III), La(III) and Nd(III) were employed and separation experiments were done by investigating the effect of some variables on the separation degree of the target metal ions. First, REEs (Ce(III), La(III) and Nd(III)) were simultaneously separated from other metal ions in the solution by double salt precipitation at ambient temperature by using Na2SO4 as a precipitant. Second, Fe(III) and Zn(II) in the filtrate were sequentially separated by one stage extraction and counter-current extraction with D2EHPA, respectively. Third, Mn(II) was separated by oxidative precipitation from the raffinate by adding NaClO. Fourth, Co(II) was separated from the filtrate containing Ni(II) by counter-current extraction with saponified Cyanex 272. Finally, the REE(III)s double salt precipitates were dissolved in hydrochloric acid solution and Ce(III) was separated from La(III) and Nd(III) by oxidative precipitation with NaClO. Then Nd(III) was separated from La(III) in the filtrate by counter-current extraction with a mixture of Cyanex 272 and Alamine 336. For all of these steps, optimum conditions were obtained, and a process was proposed for the recovery of the valuable metals present in spent Ni-MH batteries.