Yoshito Wakui

Hydrometallurgical process for recovery of metal values from spent nickel-metal hydride secondary batteries

Abstract A completely hydrometallurgical process has been developed for the recovery of metal values such as cobalt, nickel and rare earths from spent nickel-metal hydride (Ni-MH) secondary batteries. Effects of hydrochloric acid concentration, temperature, reaction time and solid-to-liquid ratio on leaching of metals contained in the electrode materials of the batteries were studied. The optimal operating conditions were found to be 3 M HCl at a temperature of 95°C and a 3-h leach time, and it was possible to treat up to 5.5 g of scrap in 50 ml of acid solution where the recoveries 100% of cobalt, over 96% of nickel and 99% of rare earths were achieved. A typical chemical composition of the resulting leach liquor was approximately, in grams per liter, 23.4 Ni, 1.7 Co, 3.4 Fe, 0.72 Zn, 0.46 Al, 1.2 Mn, 4.2 La, 0.26 Ce, 0.82 Pr, 2.6 Nd and 0.074 Sm, as well as 50 Cl. The pH of the solution was around 1.2. The rare earth values can be readily recovered from the leach liquor by the use of a solvent extraction circuit with 25% bis(2-ethylhexyl) phosphoric acid (D2EHPA) in kerosene, in which a two-stage counter-current extraction at an O:A ratio of 3:1 at an equilibrium pH of 2.0, a single-stage cobalt scrubbing with 0.3 M hydrochloric acid at an O:A ratio of 22:1, and a stripping operation with 2.0 M hydrochloric acid in one contact at an O:A ratio of 5:1 are involved. A mixed rare earth oxide of over 99% purity was obtained by selective precipitation with oxalic acid, and calcination of the precipitate. The total yield of rare earths approached 98%. The cobalt and nickel in the raffinate are effectively separated by selective extraction of cobalt with 25% TOA in kerosene after concentration (up to [Cl−]≈220 g l−1). Nearly complete recovery of cobalt can be achieved by using a three-stage counter-current extraction at an O:A ratio of 2:1, followed by stripping with a dilute hydrochloric acid solution (pH 2.0) in a single stage at an O:A ratio of 4:1. Subsequently the cobalt in the strip liquor and the nickel remained in the raffinate are separately recovered as oxalates by the addition of ammonium oxalate. A pure cobalt product and a nickel oxalate with a purity close to 99.9% were obtained. The total recoveries of cobalt and nickel were found to be approx. 98% and 96%, respectively.

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

Abstract A hydrometallurgical process is developed for the separation and recovery of metal values such as nickel, cobalt and rare earths from spent nickel–metal hydride (Ni–MH) rechargeable batteries. After removal of the external case, the electrode materials are dissolved in 2 M sulfuric acid solution at 95°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-ethylhexyl) phosphoric acid (D2EHPA) in kerosene, followed by precipitation with 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 approaches 93.6%. The cobalt and nickel in the raffinate are effectively separated by solvent extraction with 20% bis(2,4,4-tri-methylpenthyl) phosphinic acid (Cyanex 272) in kerosene. The individual cobalt and nickel are then recovered as oxalates by the addition of oxalic acid. Cobalt and nickel oxalates 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 flowsheet of the process for recovery of rare earths, cobalt and nickel from spent Ni–MH batteries is proposed.

Extraction of rare earth elements with 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate impregnated resins having different morphology and reagent content

Abstract Extraction of rare earth elements (REEs) with reagent impregnated resins (RIRs) using 2-ethylhexyl hydrogen 2-ethylhexyl phosphonate (PC-88A) and Amberlite XAD-2, XAD-4, XAD-16 and XAD-7 as a polymeric support has been studied. The impregnated resins containing various amounts of PC-88A have been prepared by a dry method. The effect of contact time on the extraction of REEs with PC-88A impregnated resins (PC-88A–resin=20/80, 50/50 wt.%) at pH 3.5 has been chiefly investigated. It was found that the extraction becomes slow when an insufficient amount of PC-88A was impregnated into XAD-2, XAD-4 or XAD-16 resins with respect to their pore volume. Little effect of the amount of PC-88A in XAD-7 on the rate of extraction was observed. The presence of n-dodecane improves the extraction kinetics for XAD-4 and XAD-16 at a small PC-88A content. It is speculated that PC-88A should be filled in the pore of the resin from the bottom to the top under the present impregnation process. It is thus recommended to make RIRs with enough of the reagent to fill up the pores of hydrophobic resins in this impregnation method.

Chromatographic separation and inductively coupled plasma atomic emission spectrometric determination of the rare earth metals contained in terbium

Abstract The chromatographic separation of rare earth elements (REEs), prior to inductively coupled plasma atomic emission spectrometric (ICP-AES) measurements, using a column packed with 2-ethylhexyl hydrogen 2-ethyl-hexylphosphonate (PC-88A)-loaded polymer resin in order to exclude spectral interferences was examined. A favourable separation of trace amounts of metals (La, Nd and Sm) from a large amount of terbium was achieved simply by elution with dilute hydrochloric acid. Trace lanthanum and neodymium in metallic terbium were determined by separation of the analyte ions from the matrix element followed by ICP-AES analysis.