PVDF-HFP based polymer inclusion membranes containing Cyphos (R) IL 101 and Aliquat (R) 336 for the removal of Cr(VI) from sulfate solutions

摘要

Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was used for the preparation of polymer inclusion membranes (PIMs) containing trihexyltetradecylphosphonium chloride (Cyphos (R) IL 101) or trioctylmethylammonium chloride (Aliquat (R) 336) for the removal of Cr(VI) from sulfate solutions. PIMs containing 50 wt% of Cyphos (R) IL 101 or Aliquat (R) 336, with corresponding thicknesses of 54 +/- 7 or 48 +/- 9 mu m, were transparent and mechanically stable. Scanning electron microscopy, atomic force microscopy, thermogravimetric analysis, stress-strain analysis, and contact angle measurements were used for characterizing PIM surface morphology, thermal and mechanical properties. The extraction experiments were performed by immersing a circular PIM segment (3.5 cm in diameter) in a 50 mL sulfate solution containing 2.0 x 10(-4) mol L-1 of Cr(VI). The optimum conditions with respect to pH and sulfate concentration were 1.2 and 0.045 mol L-1, respectively. The results indicated a higher extraction rate of Cr(VI) by the PIM containing Cyphos (R) IL 101 in comparison with that achieved by the Aliquat (R) 336 based PIM. Analysis of the extraction data confirmed that the main extracted species into both PIMs was HCrO4-. A variety of stripping reagents were tested and best results were obtained with 1.0 mol L-1 NaNO3 which allowed efficient back-extraction of Cr(VI) from the loaded PIMs containing Cyphos (R) IL 101 or Aliquat (R) 336. The extraction capacity of the Cyphos (R) IL 101 and Aliquat (R) 336 based PIM was 71 mg and 70 mg of Cr per 1 g of membrane and they could be reused for 16 and 6 consecutive extraction/back-extraction cycles, respectively. It was found that the mass loss of the Cyphos (R) IL 101 PIMs in these experiments was significantly lower than that observed for the Aliquat (R) 336 based PIMs. These results illustrated the excellent stability of the Cyphos (R) IL 101 based PIM. Both Cyphos (R) IL 101 and Aliquat (R) 336 based PIMs did not experience interference in the extraction of Cr(VI) by other common cations. The Cyphos (R) IL 101 based PIM extracted selectively Cr(VI) in the presence of up to 500 fold excess of nitrate and chloride anions, while this selectivity was limited to 10 fold for the Aliquat (R) 336 based PIM. The potential of both PIMs for practical applications was demonstrated with the removal of Cr(VI) from well water and industrial wastewater.