EXTRACTION OF CR(VI) WITH ALIQUAT-336 IN HOLLOW-FIBER CONTACTORS - MASS-TRANSFER ANALYSIS AND MODELING

In this work the mass transfer analysis and modeling of the hollow fib er non-dispersive liquid-liquid extraction of Cr(VI) with Aliquat 336 is reported. Experimental results corresponding to different values of the initial concentration of Cr(VI) in the aqueous phase in the range 50 g/m3 less-than-or-equal-to C0 less-than-or-equal-to 500 g/M3 Showe d three different diffusional regimes depending on both the initial co ncentration of Cr(VI) and the linear velocities of the aqueous phase: (i) kinetic control of the mass transport in the aqueous phase, (ii) k inetic control of the mass transport through the membrane fiber wall a nd (iii) an intermediate region where the control is shared between th e aqueous and the membrane phases. The integration of the mass conserv ation equation with a nonlinear equilibrium condition at the fiber wal l agrees satisfactorily with the results of experiments performed at d ifferent initial concentrations of Cr(VI) and different values of the linear velocity of the aqueous phase in the range C0 greater-than-or-e qual-to 50 g/m3 and 2.95 x 10(-3) m/s less-than-or-equal-to v less-tha n-or-equal-to 1.18 x 10(-2) m/s. An optimization of the parameters D, solute diffusivity in the aqueous phase, and K(eq), equilibrium consta nt of the extraction chemical reaction, with all the experimental resu lts, using as criterion the minimum weighted standard deviation, gave as a result the value of the parameter D = 2.3 x 10(-9) m2/s and value s of K(eq) dependent upon the initial concentration of Cr(VI) in the f eed solution. The mass transfer model and parameters reported in this work are useful for the design and optimization of the nondispersive e xtraction of Cr(VI) in a hollow fiber module.