Dispersion-Free Solvent Extraction of Cr(VI) from Acidic Solutions Using Hollow Fiber Contactor

The use of dispersio´n-free solvent extraction, through microporous hydrophobic membrane has been investigated. The hollow fiber contactor, with surface area of 1.4 m2 was used to extract Cr(VI) (0.005-0.12 g/L) from aqueous sulphuric acidic media (pH 2.5-4.2 ( 0.05). Several parameters such as extractant concentration, feed acidity and metal concentration in the initial aqueous solution were investigated. Results revealed that 15% v/v Cyanex 923 in Exxsol D-100 as organic phase and feed in the 2.5 pH range, gave optimum extraction (exceeding 95%) of Cr(VI) and it was possible to strip using 10 g/L hydrazine sulfate (also with recoveries exceeding 95%). In this step, Cr(VI) is immediately reduced to the less hazardous Cr(III) state. Results also showed that under the various experimental conditions, chromium(VI) extraction was ratecontrolled by the interfacial reaction on the membrane surface. Typical overall mass transfer coefficients values are 4.2 × 10-5 and 3.6×10-6 cm/s for extraction and stripping operations, respectively.We thank the CSIC for support.Peer reviewe