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Abstract: A hydrometallurgical procedure has been developed for the separation and recovery of nickel, cobalt and rare earths (RE) from spent Ni–MH batteries. In the process of separation and recovery, the positive and negative electrode materials were merged and leached with 3M H2SO4 at 95°C. In this stage, about 94.8% of rare earths were separated from other metals due to the low solubility of RESO4 at relatively high temperature. Then iron, zinc and manganese (together with the remaining 5.2% rare earths) were almost completely separated from nickel and cobalt by solvent extraction with 20% P204. Rare earths in the organic phase were recovered by stripping with 2M HCl after scrubbing Zn and Mn. Most rare earth sulphates remaining in the leach residue were transformed to RE(OH)3 by treatment with NaOH and then redissolved from the filter cake as RECl3 by using the rare earth strip liquor and additional HCl. Cobalt was easily separated from nickel by solvent extraction with 20% Cyanex 272 and pure cobalt and nickel sulphates were recovered from evaporation of the strip liquor and raffinate respectively. Finally, spherical nickel hydroxide powder was synthesized from the pure nickel sulphate, which is an important starting material for Ni–MH batteries. The overall recovery efficiency for rare earths, cobalt and nickel exceeded 98%. [Copyright &y& Elsevier]

Abstract: Efficient new extractant design relies on systematic structure–property studies. However, systematic structure–property research on extractants of organic phosphinic acids is far from sufficient. To make up for this deficiency, twelve organic phosphinic acid extractants (including nine dialkylphosphinic acids, two dicycloalkylphosphinic acids and one diarylphosphinic acid) were synthesized with free-radical-addition-reaction method and Grignard-reaction method. Reaction rules, advantages and disadvantages of these two methods were discussed respectively. The extraction ability and separation performance of the synthesized organic phosphinic acids for Tm, Yb and Lu from HNO3 solutions were evaluated and compared. For dialkylphosphinic acids the nearer the branched chain moved to P atom, the more reduction generated on the extraction ability. Dialkylphosphinic acids without branched chain in α-C or β-C (e.g. HYY-3, HYY-5, HYY-7 and HYY-9) exhibited strong extraction ability as P507. On the contrary, dialkylphosphinic acids with branched chain in α-C (e.g. HYY-4, HYY-8) and dicyclohexylphosphinic acids exhibited poor extraction ability as Cyanex 272. New compound Di-(2,3-dimethylbutyl)-phosphinic acid (HYY-2) exhibited good extraction ability and separation performance and its separation factors of Lu/Yb, Yb/Tm and Lu/Tm were 1.42, 3.10 and 4.40 respectively, apparently superior to Cyanex 272 (βLu/Yb =1.31, βYb/Tm =3.25, βLu/Tm =4.26). [Copyright &y& Elsevier]

The extraction and separation of heavy rare earths is always one of the most challenging unit operations in hydrometallurgy. Research and development of novel efficient extractant is one way to solve this problem. Organophosphinic acid is a good potential extractant. A new method was established for the synthesis of nonsymmetric dialkylphosphinic acid (NSDAPA) (R′R″POOH, R′ ≠ R″), optimized the synthesizing conditions of the key intermediate mono-alkylphosphinic acid and successfully synthesized three novel extractants ( n -octyl)(2,4,4′-trimethylpentyl) phosphinic acid, ( n -octyl)(cyclohexyl)phosphinic acid and (2,3-dimethylbutyl) (2,4,4′-trimethylpentyl)phosphinic acid. The extraction ability of the novel extractants was investigated. The structure–property relationship and the separation performance for heavy rare earth couples Er/Y, Y/Ho, Yb/Tm and Lu/Yb were evaluated. [ABSTRACT FROM AUTHOR]