Kinetic Separation of Nickel(II) and Cobalt(II) with 5-Octyloxymethyl-8-quinolinol by Differential Extraction

Abstract

The extraction rate-controlled separation of nickel(II) from cobalt(II) with 5-octyloxymethyl-8-quinolinol (HO₈Q) and the kinetics of the extraction of nickel(II) and cobalt(II) with HO₈Q are described. The extraction rate was first-order regarding metal ions and HO₈Q, and was inverse first-order regarding hydrogen ions. The extraction rates were represented by -d[M²⁺]/dt={k_HL+k_L[H⁺]^-1K_a}K^-1_DR[M²⁺][HO₈Q], where K_a and K_DR are the acid-dissociation constant of the hydroxy group of HO₈Q and the distribution constant of HO₈Q between chloroform and water, respectively. The values of k_HL were determined to be 4.2×10³mol^-1 dm³ s^-1 and 4.7×10⁴mol^-1 dm³ s^-1 for nickel(II) and cobalt(II), respectively, at 25°C and l=0.1mol dm^-3 (NaClO₄). The k_L are to be 7.1×10⁸mol^-1 dm³ s^-1 and 6.0×10¹⁰mol^-1 dm³ s^-1 for nickel(II) and cobalt(II), respectively, under the above-mentioned conditions. The rate-determining steps should be the competitive reactions of metal ions with the neutral and anionic forms of HO₈Q. The procedure for a rate-controlled separation of nickel(II) from cobalt(II) are as follows: A mixture composing ten cm³ of the aqueous solution containing 3.00×10^-5mol dm^-3 metal ions and an acetate buffer at pH 4.6 was vigorously shaken with a 10cm³ of 5.0×10^-2mol dm^-3 HO₈Q chloroform solution for 2min. The separation efficiency was more than 95%.