Abstract: A new extractant, [N,N-di(2-ethylhexyl)amino]methylphenylphosphinic acid (DEAPP), was synthesized to develop the mutual separation techniques of In(III), Ga(III) and Zn(II). The extraction selectivity for In(III), Ga(III) and Zn(II) with DEAPP was higher than that of the commercial phosphorus acid extractants such as D2EHPA and PC-88A. The extraction selectivity for metal ions in 1 mol·L^-1 aqueous ammonium nitrate solution with DEAPP was in the following order: In(III) > Ga(III) > Zn(II). These selective extraction behaviors indicate that the amino moiety of DEAPP plays an important role in the mutual separation of In(III), Ga(III) and Zn(II). The extraction equilibria of In(III), Ga(III) and Zn(II) with DEAPP (=HR) were expressed by the following reactions: In³⁺+2(HR)₂ ⇋InR₃(HR)+3H⁺, Ga³⁺+1.5(HR)₂+NO₃^- ⇋GaR₂(HR)(NO₃)+2H⁺, and Zn²⁺+2(HR)₂ ⇋ ZnR₂(HR)₂ + 2H⁺. The extraction equilibrium constants of In(III), Ga(III) and Zn(II) with DEAPP were determined to be Kex,M=1.7 × 10⁴ [dm³·mol^-1], 4.17 [(dm³·mol^-1)^0.5], and 1.55 x 10^-2 [-], respectively.

Key words: Liquid-liquid extraction, Phosphinic acid, Indium(III), Gallium(III), Zinc(II), Mutual separation, Extraction equilibrium