Recovery of metal values from spent nickel-metal hydride rechargeable batteries

A hydrometallurgical process is developed for the separation and recovery o f metal values such as nickel. cobalt and rare earths from spent nickel-met al hydride (Ni-MH) rechargeable batteries. After removal of the external ca se, the electrode materials are dissolved in 2 M sulfuric acid solution at 95 degrees C. The resulting liquor contains typically (g l(-1)), 10.6 Ni, 0 .85 Co, 1.70 Fe, 0.36 Zn, 0.21 Al, 0.54 Mn, 1.73 La, 0.10 Ce, 0.33 Pr, 1.10 Nd and 0.032 Sm. The pH is around 0.4. The rare earth values are recovered from the liquor by means of a solvent extraction circuit with 25% bis(2-et hylhexyl) phosphoric acid (D2EHPA) in kerosene, followed by precipitation w ith oxalic acid. A mixed rare earth oxide of about 99.8% purity is obtained after calcination of the precipitate. The total yield of rare earths appro aches 93.6%. The cobalt and nickel in the raffinate are effectively separat ed by solvent extraction with 20% bis(2,4,4-tri-methylpenthyl) phosphinic a cid (Cyanex 272) in kerosene. The individual cobalt and nickel are then rec overed as oxalates by the addition of oxalic acid. Cobalt and nickel oxalat es with purities close to 99.6% and 99.8%, respectively, are obtained. The overall recoveries are over 96% for both cobalt and nickel. A total flowshe et of the process for recovery of rare earths, cobalt and nickel from spent Ni-MH batteries is proposed. (C) 1999 Elsevier Science S.A. All rights res erved.