Transport of chromium(III) from mixtures of chromium ions by CTA- and PVC-based inclusion membranes.

The author analysed the stability of cellulose triacetate (CTA)- and poly(vinyl chloride) (PVC)-based polymer inclusion membranes (PIMs) containing bis(2-ethylhexyl) phosphoric acid (D2EHPA) as a carrier for chromium(III) separation from mixtures of Cr(III)/Cr(VI) ions. He also studied the influence of carrier (D2EHPA) concentration in PVC- and CTA-based PIMs on chromium(III) ion transport, at different initial concentrations of the Cr(III) ions. Based on the results, the optimum range of carrier concentration in both membranes guaranteeing the fastest process was found. Moreover, PIMs with D2EHPA as the carrier worked as selective barriers for Cr(VI) ions. However, in the case of CTA/PIM, the increase in Cr(VI) concentration above 0.005 mol/dm3 negatively influenced Cr(III) transport, which was caused by the degradation of the polymer matrix. The PVC/PIM was not influenced by the Cr(VI) ions, thus PVC was definitely a better polymer for the synthesis of PIM for the separation of Cr(III/VI) ions. It was also demonstrated that both membranes were not stable over a long process time. The results reported in this study suggest that the factor that determines the stability of PIMs with D2EHPA is the presence of water in the membrane and the formation of unstable micellar structures.

Supported liquid membrane system for Cr(III) separation from Cr(III)/Cr(VI) mixtures.

This paper presents the results of analyses of the chromium(III) transport process from mixtures of Cr(III)/Cr(VI) ions using supported liquid membranes (SLM), in which dinonylnaphthalene sulfonic acid (DNNSA) and di(2-ethylhexyl) phosphoric acid (D2EHPA) were used as carriers. In both cases the membrane worked as a selective barrier for Cr(VI) ions. The increase in both the time of Cr(VI) ions-carrier interaction and the Cr(VI) concentration in the feed phase negatively influenced the Cr(III) separation. The polarizing layer consisting of Cr(VI) ions prevents the access of Cr(III) ions to the inter phase surface and leads to the deactivation of the carrier, which is the result of the strong oxidation properties of Cr(VI) ions. These factors meant that, in the case of the membrane with DNNSA, the membrane could not be used for the effective separation of Cr(III) from the Cr(III)/Cr(VI) mixture. On the other hand, the membrane with D2EHPA can be used for fast and efficient transport of Cr(III) ions, but only for strictly defined process parameters, i.e. where the level of chromium(VI) concentration is below 10(-3)M and with intensive feed phase mixing.