Equilibrium in the partitioning of Zn(II) between aqueous sulphate solution and kerosene solution of Cyanex 272

The equilibrium in the partitioning of zn(ii) from its sulphate solution to bis-(2,4,4-tri- methylpentyl) phosphinic acid (cyanex 272,btmppa,h 2a2) solution in kerosene (paraffin) has been investigated extensively. the equilibration time is < 5 min. extraction of zn(ii) is found to be increased with increasing equilibrium ph,extractant concentration and temperature; and independent of [zn(ii)] in the aqueous phase provided equilibrium ph and extractant concentration are kept constant. the ph dependence of extraction ratio (d) at a constant [h2a2](o,eq) is found to be 2. the extractant dependence plots at constant equilibrium ph values are not straight lines but are curves with asymptotic slopes of 1 and 2 at lower concentration region (lcr) and higher concentration region (hcr) of extractant,respectively. d is found to be an inverse function of (1 + 2[so 4 2-]). the extraction at lcr of extractant is found to occur through the reaction: zn2+ + h2a2 (o) ⇌ [zna2](o) + 2 h+; but at hcr of extractant,it occurs via the reaction: zn2+ + 2 h2a2 ⇌ [zna2.h2a2](o) + 2 h+. the extraction equilibrium constants,kex at lcr and hcr of extractant are estimated as 10-3.11 and 10-2.08,respectively,at 303 k. the extraction process is found to be endothermic but ah value increases with increasing extractant concentration. the maximum loading capacity is estimated to be 11.5 g zn(ii) per 100 g extractant. at a maximum loading,the species exists in organic phase is zna2. the stripping ability of various inorganic acids towards loaded zinc,as well as,the possibilities of separation of zn(ii) from its binary mixtures with 3d - block metal ions have also been investigated.