Preparation and examination of potential of polymer inclusion membranes containing crown ethers towards Cr(VI)

Recently membrane based processes have attracted attention as a valuable technology for many industries. Polymer inclusion membranes (PIMs) are a type of liquid membranes has developed because of their chemical and mechanical stability that even higher than supported liquid membranes (SLMs).[1] Thus, PIMs can be reused for several times without significant decreasing in their application.[2] PIMs are thin and flexible films that are formed by casting an organic solution containing an extractant, a base polymer and, if necessary, a plasticizer.[3] In the extraction experiments from the sulfate medium the effect of parameters including pH, extraction time and sulfate ion concentration were evaluated. The maximum extraction of the analyte was found under conditions: pH 1, extraction time 20 h, sulfate concentration 0.6 M. The effect of the type of electrolyte used was also assessed by comparison the extraction percentage of Cr(VI) by the PIMs from the aqueous solutions formed by potassium sulfate (0.6 M, pH 1), sulfuric acid (0.6 M), KCl (1.2 M) and HCl (1.2 M). The extraction percentage was highest in hydrochloric acid solutions. This arouse us to examine the effect of the acid concentration, in the range 0.6-3 M, on the extraction process. The optimal value was 1.2 M. The back-extraction experiments of the loaded PIMs were studied with 50 mL nitric acid, perchloric acid, sodium nitrate, sodium sulfite, sodium thiosulfate, ammonium acetate and sodium hydroxide. The highest value of back-extracted Cr(VI) was achieved by 0.1 M NaOH. The experimental capacity of PIM was evaluated under optimum conditions as a function of initial Cr(VI) concentration. The capacity of the PIMs was found to be 3.6 mg chromium/g PIM. It is found that the presence Pb2+, Ni2+, Cd2+, Zn2+ and NO3- with concentrations up to 10 times higher than the chromium ions concentration did not an interference effect on the Cr(VI) extraction.