Selective extraction of Cr(VI) over metallic species by polymer inclusion membrane (PIM) using anion (Aliquat 336) as carrier

Extraction and transport of chromium were carried out by using polymer inclusion membrane (PIM) containing Aliquat 336 as specific carrier. Cellulose triacetate (CTA) and polyvinyl chloride (PVC) (three different types of PVC) were used as polymer matrix for preparing the PIM. The fraction of Aliquat 336 was varied to determine the optimum composition with respect to physical properties and extraction capability of the membranes. The effect of polymer matrix, plasticizer characteristic, carrier concentration, and feed and strip phase composition were investigated on the transport of Cr(VI). In feed phase containing 2 · 10−4 M Cr(VI) at pH 1.2 (H2SO4), 80% of Cr(VI) was transported through the PIM in 8 h by using 0.1 M NaOH as stripping phase. In these conditions, chromium(VI) concentration in the source aqueous phase was reduced from 10 · 2 mg L−1 to 0.2 mg L−1 (the maximal concentration of chromium tolerated being 0,5 mg L−1 in discharges). Competitive transport of various metallic ions was performed and it was shown that the composition of the feed based on anionic species SO42− was an important parameter to get selective and efficient PIM towards Cr(VI) transport. The metal ions Ni(II), Zn(II), Cd(II) and Cu(II) were not transported through the PIM, while a very weak percentage of the Zn(II) was transported (0.12 %). However, a high recovery factor (92 %) of Cr(VI) was obtained, indicating that HCrO4−, present in the studied range of H2SO4 concentration, had the highest affinity to the ionic carrier.