Chromium removal by emulsion liquid membrane using [BMIM]+[NTf2]− as stabilizer and TOMAC as extractant

A new type of emulsion liquid membrane (ELM) has been prepared to separate and concentrate chromium (Cr) from waste water. A hydrophobic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM]+[NTf2]−) is used in the membrane phase as a stabilizer to provide sufficient stability and a second ionic liquid Tri-n-octylmethylammonium chloride (TOMAC) as a carrier. The other components to prepare emulsion are kerosene as solvent, span 80 as surfactant and NaOH as an internal reagent. In the present experimental investigation, the effects of various parameters such as homogenization speed, carrier concentration, internal phase concentration, agitation speed, treat ratio, internal to membrane phase ratio, surfactant concentration, pH of the feed phase and ([BMIM]+[NTf2]− concentration on the % removal of Cr have been reported. At an optimum condition, 97% percentage of Cr could be extracted. Results showed that the stabilizing effect of [BMIM]+[NTf2]− keeps on decreasing as the extraction proceeds. However, the provided stability by the combination of [BMIM]+[NTf2]− and span 80 has been found to be sufficient during the extraction process.

Research Highlights
► Ionic liquid [BMIM]+[NTf2]– was found to play the role of a stabilizer in ELM.
► Mechanism of Cr-carrier complex transportation has been explained with TOMAC.
► Various parameters affecting the final removal of Cr were have been studied.
► 97% of Cr could be removed from waste-water at optimum conditions.