Carrier-mediated transport of Cr(III) across Lasalocid A-NPOE supported liquid membrane

Abstract

A weak amount of Cr(III), not exceeding 5%, was transported through a flat sheet supported liquid membrane (FSSLM) using Lasalocid A as carrier and nitric acid as stripping agent. This inefficient transport was mainly due to a driving force disappearance caused by a nitric acid leakage through the flat sheet membrane and then a feed pH decrease. Three experimental solutions have been proposed to overcome, at least partially, this hindrance. Firstly, Cr(III) was transported across a hollow-fiber supported liquid membrane (HFSLM) working as a column system, i.e., by recirculating the feed solution and the stripping solution separately and successively. A transport rate of 19% has been found when each solution was recirculated for 24 h. Secondly, tributyl phosphate (TBP) was used as modifier of the organic membrane solution to accelerate reaction kinetics to interfaces. The addition of TBP permits the transport of 17% of the initial Cr(III) amount in feed after 79 h of the transport process. Thirdly, the feed pH was kept constant by the addition of concentrated NaOH solution. This addition led to a complete Cr(III) transport and an initial flux of 4.1×10 −7 mol.m −2.s −1 was obtained.