Synergistic extraction and separation of chromium(III) from acidic solution with a double-carrier supported liquid membrane

This study describes the effect of two components used as carriers on the transport mechanism of chromium(III) ions through double-carrier supported liquid membrane (DCSLM). The di(2-ethylhexyl) phosphoric acid (D2EHPA) and bis(2,4,4-trimethylpentyl) phosphinic acid (CYANEX272) were used as a carriers. The structure of selected carriers is typical for the amphiphilic substances, showing ability to aggregates formation within the membrane phase. Based on water determination in the membrane phase and critical micelle concentration of the carriers (CMC), the authors proposed the formation of the non-spherical aggregates into the membrane system. This, together with the experiments on extraction of Cr(III) ions allowed to conclusion that the role of the D2EHPA is to create “transport tunnels” for chromium flow through the membrane. The role of the CYANEX272 in the membrane, on the other hand, is to extract Cr(III) ions from the feed phase and to stabilize of the D2EHPA “transport tunnels”. Such stable “transport tunnels” facilitate flow of Cr(III) ions through the membrane. This transport mechanism was characterized as the “flow-type” mechanism.