A comparison of the use of commercial and diluent free LIX84I in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)-based polymer inclusion membranes for the extraction and transport of Cu(II)

Abstract

The active component of the commercial extractant LIX84I, i.e. 2-hydroxy-5-nonylacetophenone (HNAPO), is usually below 50 wt%. The separation performance of polymer inclusion membranes (PIMs) generally increases with increasing the concentration of their liquid phase, consisting of the extractant (e.g., LIX84I) and a possible plasticizer or modifier. However, the use of high concentrations of the membrane liquid phase leads to worsening of the PIM mechanical stability. Therefore, the only way of increasing the concentration of HNAPO in PIMs without affecting their mechanical stability can be based on using diluent free LIX84I with concentration of HNAPO significantly higher than that in commercial LIX84I. This paper reports on a comparison between the performance of PIMs composed of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as the base-polymer, commercial or diluent free LIX84I as the extractant and 2-nitrophenyloctyl ether (NPOE) as the plasticizer when used for the extraction and transport of Cu(II) from ammonium sulfate solutions at pH 8.5. The diluent free LIX84I, obtained by a precipitation method, together with commercial LIX84I were characterized by gas chromatography-mass spectrometry and Fourier transform infrared spectroscopy. The percentage of HNAPO was determined by solvent extraction of Cu(II) and found to be 49 wt% and 72 wt% for the commercial and diluent free LIX84I, respectively. A comparative study between commercial and diluent free LIX84I-based PIMs was performed with regards to the extraction and transport of Cu(II) as well as their long term stability. Unexpectedly, the PIMs containing commercial LIX84I performed slightly better than the PIMs containing diluent free LIX84I in terms of extraction and transport rate of Cu(II). A selectivity study showed that both commercial and diluent free LIX84I-based PIMs had good selectivity for Cu(II) in the presence of Zn(II), Mg(II), Ni(II), and Co(II) in ammonium sulfate solutions, although the PIM containing commercial LIX84I was able to separate Cu(II) faster than the one composed of diluent free LIX84I.