Data for the extraction of chromium,
Cr(VI), from aqueous acidic
chloride and nitrate solutions by Alamine 300 (tertiary amine)/xylene
and di-n-octyl amine (DOA)/xylene solvent systems
(298 K) have been subjected to formulation of an optimization structure
for an effective Cr(VI) separation. The optimization approach uses
a derivative variation method to efficiently identify the optimization
range through analyzing the first-order derivatives of the optimized
quantity and the nonlinear deviation profile of the derivative value.
The main characteristics of it are simplicity and suitability for
generalization. Optimum Cr(VI) removal efficiencies, defined both
experimentally and analytically, range from about 70 to 90% for Alamine
300 and from 50 to 70% for DOA, being dependent about equally strongly
on the types and concentration levels of the amine, acid, and the
transferred Cr(VI) species. These dependencies are rationalized in
terms of the interactions that take place in the equilibrium phases.
Three independent variables, i.e. the concentrations of the amine,
acid, and Cr(VI), are adequate for expressing the nonlinear dependence
of the optimized extraction factor (E, Z
t) on the properties of relevant system. Modeling efforts
based on the LSER (linear solvation energy relation) principles and
the mass–action law methodology have shown considerable success.
The proposed LSER-based solvation model using nine physical descriptors
of the solvent and ion provides relatively reliable fits with a mean
error of 9%, and satisfies established limiting behavior of the physical
event. A critical comparison of the present method with the other
commonly used reactive extraction methods on an efficiency basis has
been carried out.