The liquid-liquid extraction of Cr(III) ions has been investigated using lasalocid A as ionophore. Chromium extraction of 92 % of the initial chromium amount (2 mL 10-3 M) by 1 mL 5.10-3 M of Lasalocid A in 2- nitrophenyl octyl ether (NPOE) has been obtained at aqueous feed pH value of 5.5. Difficulties correlated to the stripping step were also studied because only 57 % of chromium was recovered by contact of the loaded organic phase with a solution of HCl at pH 0 was obtained. The incomplete stripping of the metal may be a result of the formation of stable species in the oragnic phase. The use of an acidic stripping solution made of HNO3 at pH 0 had permitted to surmount this hindrance and to obtain a stripped ratio of 89 %. The study of Cr(III) transport through a supported liquid membrane (SLM) and under the same optimum conditions, demonstrated a very low extraction ratio. The weakness of this ratio can he explained by a HNO3 leakage through the membrane, which in turn leads to a pH decrease in the source phase to acidic pH values where the extraction becomes impossible. This HNO3 leakage was confirmed by pH measurements and by circulating separately the source phase and the stripping phase successively (0.8 mL.min-1) through a hollow fibre SLM device (acting as a column system) where a recovery yield of 19 % was obtained after a circulation time of 24 h for each aqueous phase.
R. Tayeb, S. Tingry, M. Dhahbi, P. Seta
Chromium, Liquid-liquid extraction, Extraction efficiency, Supported liquid membrane (SLM)