Separation of Co(II) and Ni(II) ions by supported and hybrid liquid membranes

Abstract

Abstract In this work a competitive transport of an equimolar mixture of cobalt(II) and nickel(II) across supported and hybrid liquid membranes is presented. In both types of membranes di-2-ethylhexylphosphoric acid (D2EHPA) as well as commercial extractants, i.e. Cyanex® 272, 301, and 302 were used as ion carriers. In experiments with the supported liquid membranes, the support applied for the liquid membrane was microporous, hydrophobic polypropylene Celgard® 2500. This film was soaked in 0.1 M organic solution of an ionic carrier in kerosene. The hybrid liquid membranes were made by composition of the cation-exchange membranes (CEM) with bulk liquid membrane in the system: CEM–organic phase–CEM. The source aqueous phase was composed of an equimolar mixture of Co(II) and Ni(II) ions in sulfuric acid aqueous solutions. As receiving phase, sulfuric acid solutions of higher concentration than the source phase were utilized. The influence of several factors on cation transport selectivity and effectiveness has been explored. These factors include the effect of (a) acidity of the source and receiving phases, (b) initial concentration of metal ions in the source phase and (c) concentration of ion carrier in membranes. It is shown that supported and hybrid liquid membranes, containing phosphoorganic acids allow to separate a Co(II)/Ni(II) equimolar mixture. The separation of Co(II)/Ni(II) was found to be governed by the ionic carrier used as well as the acidity of the aqueous source phase. In the hybrid liquid membrane processes lower metal ion fluxes than in supported liquid membranes processes were observed. On the other hand, higher separation coefficients for Co(II)/Ni(II) were found for hybrid than for supported liquid membrane processes.