Separation of chromium and nickel ions by supported liquid membranes using TOA as carrier

The extensive use of chromium in leather tanning, metallurgy, electroplating and other industries has resulted in the release of aqueous chromium to the subsurface at numerous sites. Cr (VI) has received considerable attention owing to its extensive industrial applications and has long been recognised as a toxic substance due to its strong oxidising  potential and the ease with which it can cross the biological membranes. In recent years the application of various solvent extraction technologies to the removal and concentration of chromium have been widely studied; chemical precipitation, ion exchange, reverse osmosis, diffusion dialysis, adsorption, liquid membrane technique are some of the alternatives that have been reported in the literature. Recently  supported liquid membrane (SLM) extraction is an alternative to conventional  solvent extraction  due  to its advantages like high selectivity, operational simplicity, low solvent inventory, low energy consumption, zero effluent  discharge  and combination of  extraction and stripping into one single unit. In this work  the selective separation of chromium from acidic media, containing the mixtures of chromium and nickel  by SLM was investigated using TOA (tri-octylamine) as carrier. The liquid membrane was consisted of  the desired  concentration of  an extractant (TOA), a modifier (TBP), and a diluent (chloroform, kerosene, cyclohexane). The membrane support was microporous hydrophobic  polypropylene Celgard 2500.  Such parameters as, the solvent type, feed solution pH, extractant (TOA) concentration, modifier (TBP) concentration and temperature were experimentally studied and the optimum conditions were determined. The permeation coefficients (P) and the initial fluxes of  chromium (J o )  were  calculated. Separation factors of  chromium  over  nickel  was calculated  from the experimental measurements.