A new supported liquid membrane (SLM) with methyl cholate for facilitated transport of dichromate ions from mineral acids: parameters and mechanism relating to the transport

The technique of supported liquid membranes (SLM) was used to achieve the facilitated transport of Cr2O72-, using an amphiphilic organic molecules as carriers, methyl cholate, widely used for facilitated transport of metal ions and carbohydrates (sugars and alditols). For our prepared SLM, toluene as organic phase and film of polyvinylidene difluoride (PVDF), as microporous and hydrophobic polymer support with 100ìm in thickness and 0.45µm as the diameter of the pores. The macroscopic parameters, permeability P and initial flux Ji, on the facilitated transport of the Cr2O72- anions were determined for several acidities of the medium of the three mineral acids: hydrochloric acid (HCl), nitric acid (HNO3) and sulfuric acid (H2SO4). For the different studied environments, the prepared SLM is highly permeable for the transported substrate (Cr2O72-), and a clear evolution of these parameters was observed for the used carrier. The initial flux on the facilitated transport of the Cr2O72- anions is related to the initial concentration of this substrate in the feed phase by a saturation law, which allowed the determination of the microscopic parameters, apparent diffusion coefficient D* and the association constant Kass of the (carrier-substrate) complexes, formed in the organic phase for the used SLM. The experimental results clearly indicate that the (carrier-substrate) complexes formed in the organic phase are unstable, which results in higher apparent diffusion coefficients D* and thus a high permeability of this membrane type, to facilitated transport on this type of oxygen anions (Cr2O72-).