Separation of Chromium (VI) By Bulk Liquid Membrane Technique

Abstract

In this work an attempt has been made for faster extraction and separation of Cr (VI) from its model solution with minimal use of carrier. Studying the effects of various process parameters viz. source and stripping phase concentration and pH on the overall performance of this bulk liquid membrane technique have been a key objective along with the membrane reusability. Aqueous solution of potassium dichromate (K2Cr2O7) was used as the source phase or model contaminant for Cr (VI) ions. 1, 2-dichloroethane was the preferred solvent used as the liquid membrane phase in this work. Aqueous solution of NaOH was found to be the effective stripping phase. Performances of several carriers had been investigated and tri-n-octylamine (TOA) was found to be the most suitable in facilitating the transport mechanism. A comprehensive kinetic study was carried out and the effect of various parameters viz. carrier concentration, feed and stripping phase concentrations and pH were studied. A key objective of this work was to achieve maximum separation of Cr (VI) with minimal carrier concentration and this work successfully reports a removal percentage of ca. 98% of Cr (VI) ions with 0.25 vol. % of TOA within a span of 2 hrs. The transport mechanism was observed to be more effective in the acidic pH range w.r.t the feed phase (ca. pH 1) whereas the optimum stripping phase concentration of NaOH was 0.3 N. Membrane reproducibility study showed that the performance of the liquid membrane remained largely unaffected even after fourfold use.