Solvent extraction of manganese from sulphate-acetato medium with Cyanex 272

Abstract

The solvent extraction of Mn(II) from sulphate-acetato medium by bis(2,4,4-trimethylpentyl)phosphinic acid (Cyanex 272, BTMPPA, H₂A­₂) dissolved in distilled aliphatic kerosene has been investigated, the equilibration time being < 5 min. It is found that the extraction ratio (<i style="">D</i>) is independent of initial or equilibrium Mn(II) concentration in the aqueous phase provided equilibrium <i style="">p</i>H and extractant concentration are kept constant. Extraction of Mn(II) is found to increase with the increase in equilibrium aqueous <i style="">p</i>H, extractant concentration in the organic phase and temperature. The <i style="">p</i>H and extractant dependences are 2 and 1 respectively, from which the extraction equilibrium reaction of Mn(II) by Cyanex 272 can be presented as Mn²⁺+ H­₂A_2(o) <img src='http://www.niscair.res.in/jinfo/Balance.gif' border=0> MnA_2(o) + 2 H⁺. Acetate is used to buffer the aqueous phase which has no effect on the extraction ratio but the coexisting sulfate ion has an adverse effect; and <i style="">D</i> is found to be inversely proportional to the term (1 + 1.9 [SO₄⁼]). The extraction equilibrium constant (K_ex) has been determined to be 10^-6.17 at 303 K. The temperature dependence data show that the process is endothermic with Δ<i style="">H</i> value of ~42 kJ/mol. At a particular set of experimental parameter, <i style="">D</i> is very much dependent on the nature of diluent used to constitute the organic phase. The loading capacity is found to be 9.52 g Mn(II)/100 g Cyanex 272. The loading study also indicates that the organic phase speciation is not changed with the extent of loading. Stripping behaviors of Mn(II) from loaded organic phase with dilute H₂SO₄, HCl and HNO₃ solutions have also been examined and it is found that quantitative stripping is possible by 0.10 mol/L solutions of these acids. Using Cyanex 272, separations of Mn(II) from its binary mixtures with Sc(III), Ti(IV), V(V), V(IV), Cr(III), Fe(III), Ni(II), Co(II), Zn(II) or Gd(III) can be achieved by single-stage or multiple-stage extractions at specified aqueous eq. <i style="">p</i>H values; but Mn(II)-Cu(II) separation is not at all possible.