KINETICS OF CHROMIUM(III) TRANSPORT THROUGH THE DOUBLE-CARRIER SUPPORTED LIQUID MEMBRANE

The kinetics of chromium(III) transport through a supported liquid membrane containing both a di-(2-ethylhexyl) phosphoric acid (D2EHPA) and bis-(2,4,4-trimethylpentyl) phosphinic acid (Cyanex272) as an ions carrier was investigated. It was found that under a characteristic concentration of the carriers into the organic phase membrane provides much higher efficiency than the membrane containing only one of the extractants. In the studied system the optimal carrier concentration in the membrane is 0.16 mol/dm(3) and 0.9 mol/dm(3) for Cyanex272 and D2EHPA, respectively. Moreover, the authors indicate that only D2EHPA can act as an individual carrier in the membrane. In the case of Cyanex272 the stable structures with chromium(III) ions are formed in the membrane, which prevents effective re-extraction. Additionally, intensive stirring of an aqueous phase in another factor that has a positive influence on the transport kinetics in the double-carrier membrane. Increasing a stirring rate up to 1200 rpm shortens the process time and allows total re-extraction of chromium.