title: Dispersion-free solvent extraction of Cr(VI) from acidic solutions using hollow fiber contactor.
abstract: The use of dispersión-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 rate-controlled by the interfacial reaction on the membrane surface. Typical overall mass transfer coefficients values are 4.2 x 10(-5) and 3.6 x 10(-6) cm/s for extraction and stripping operations, respectively.
authors.affiliation: Centro Nacional de Investigaciones Metalúrgicas (CSIC), Ciudad Universitaria, Madrid, Spain.
authors.forename: Francisco J
authors.initials: FJ
authors.lastname: Alguacil
authors.forename: Manuel
authors.initials: M
authors.lastname: Alonso
authors.forename: Félix A
authors.initials: FA
authors.lastname: Lopez
authors.forename: Aurora
authors.initials: A
authors.lastname: Lopez-Delgado
authors.forename: Isabel
authors.initials: I
authors.lastname: Padilla
mesh_terms: D005591:Chemical Fractionation / Q000379:methods; D002857:Chromium / Q000302:isolation & purification*; D006834:Hydrazines / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009994:Osmolar Concentration; D010084:Oxidation-Reduction
chemical_list: D006834:Hydrazines; D002857:Chromium; C074702:chromium hexavalent ion; C029424:hydrazine