Extraction of chromium (VI) from sulphuric acid aqueous solutions by a liquid surfactant membrane (LSM)

Experimental results for the batch extraction of chromium (VI) from sulphuric acid aqueous solutions using a liquid surfactant membrane (LSM) are presented. Effects of various parameters such as time and speed of emulsification, internal phase concentration, extractant concentration, choice and concentration of surfactant, contact time, stirring speed, choice of diluent, and volume ratios of the membrane phase to internal stripping phase and that of the water-in-oil emulsions to the aqueous external phase on the membrane stability were studied. The membrane phase consists of hexane as diluent, tributyl phosphate, as extractant, and sorbiton monooleate (Span 80) as surfactant. A NaOH solution is the internal aqueous phase. Results show that with proper adjustment of experimental conditions the stability of the membrane can be enhanced to a great extent. This study also examined the effects of the concentrations of feed phase acid, metal ions, and carrier on the extraction of Cr(VI) ions. Further, the extraction kinetics of the metal ions by LSMs was examined. The results also showed that by appropriate selection of the extraction and stability conditions, nearly all of the Cr(VI) ions present in the continuous phase were extracted within a few minutes. The influence of the NaOH concentration on stripping efficiency was investigated.