Synthesis of novel nonsymmetric dialkylphosphinic acid extractants and studies on their extraction–separation performance for heavy rare earths

• Preparation and purification of monoalkylphosphinic acid were optimized.
• A new method for synthesis of nonsymmetric dialkylphosphinic acid (NSDAPA) was established.
• Three novel NSDAPA extractants were synthesized.
• Extraction and separation performance of NSDAPA for heavy rare earth metals were investigated.

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.