Polymer inclusion membranes composed of poly(vinylidene fluoride-co-hexafluoropropylene) and trihexyltetradecylphosphonium chloride, or trioctylmethylammonium chloride: kinetics and isotherms of Cr(VI) removal

The kinetics and isotherms of Cr(VI) removal from sulfate solution by two polymer inclusion membranes (PIMs) composed of poly(vinylidenefluoride-co-hexafluoropropylene) (PVDF-HFP), as a polymer base, and trihexyltetradecylphosphonium chloride (Cyphos (R) IL 101) or trioctylmethylammonium chloride (Aliquat (R) 336) with a weight percent ratio of 50/50 were investigated. This investigation was done based on batch extraction experiments. It was suggested that a Cr(VI) uptake is followed by an anion exchange mechanism, in which the chloride ion of the extractants is replaced by HCrO4- species. A pseudo-second-order model could predict the adsorption kinetic behaviour well, and the kinetic tests showed that the adsorption of Cr(VI) onto the studied PIMs occurred based on a chemisorption process. The maximum adsorption capacities of Cr(VI) on PIMs including Cyphos (R) IL101 and Aliquat (R) 336 were experimentally determined as 72.55 and 70.85 mg Cr/g PIM, respectively. The experimental results were fitted using Langmuir, Freundlich, and Dubinin-Radushkevich (D-R) isotherm models to find out the best model for predicting the isotherms of uptake of Cr(VI) by the studied PIMs. It was found that the adsorption isotherm was best matched by the Langmuir equation. The maximum adsorption capacity value (q(max)) calculated by the Langmuir model was 72.99 and 73.53 mg Cr(VI) per gram of PVDF- HFP/Cyphos (R) 101 and PVDF-HFP/Aliquat (R) 336 PIMs, respectively. The isotherm parameters value 0 < R-L < 1, 1/n < 1 and E > 8 showed that the Cr(VI) adsorption onto the prepared PIMs is favorable and chemisorption. [GRAPHICS] .