The use of poly(vinylidenefluoride-co-hexafluoropropylene) for the preparation of polymer inclusion membranes. Application to the extraction of thiocyanate

Abstract

Abstract The successful use of the solvent evaporation casting technique for the preparation of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) based polymer inclusion membranes (PIMs) is described for the first time. PIMs consisting of 70 wt% PVDF-HFP as the base polymer and 30 wt% Aliquat 336 as the carrier were prepared by the solvent evaporation casting and phase inversion techniques from solutions of the membrane components in tetrahydrofuran (THF) and N,N-dimethylformamide. These PIMs were compared in terms of their ability to extract the thiocyanate anion as a model target chemical species whose removal from gold mining process and tailings waters is of considerable technological and environmental interest. Best results were achieved with the PIMs produced by solvent evaporation from THF solutions. These membranes were translucent, flexible and homogeneous. Scanning electron microscopy images did not reveal the presence of a pore structure. The 30 wt% Aliquat 336 PVDF-HFP-based PIMs also exhibited significantly higher extraction and back-extraction rates for SCN− and long-term stability compared to PVC-based PIMs containing the same Aliquat 336 concentration. The results obtained in this study indicate that the use of PVDF-HFP as the base polymer in PIMs, prepared by conventional solvent evaporation casting, improves their performance in comparison to PIMs with traditionally used polymers such as poly(vinyl chloride) (PVC) and cellulose triacetate (CTA).