Modeling of the cadmium transport through a bulk liquid membrane

The model of metal ion permeation through a bulk liquid membrane (BLM), based on the Nernst-Planck equation, was developed. It was satisfactorily tested using the experimental data on the cadmium permeation from Cd(NO3)(2) solution through BLM (D2EHPA in kerosene) to 1 M H2SO4 solution. According to the model simulations, the cadmium permeation was controlled by K-eq on the feed side; the knowledge of the exact K-eq value on the strip side under the condition c(H2SO4) >> c(Cd) was not required. None of the following: an assumed Cd-D2EHPA complex (CdP2(HP)(2), CdP2HP), presence of undimerized D2EHPA in BLM, or ion pair formation (Cd2+ center dot SO42-) in the strip solution, influence the goodness of fit. Assuming the model based on the Fick's law with the constant cadmium mass transfer coefficient, a large dispersion of its optimal fitting values which depends on the model assumption was found. Thus, that coefficient can only be treated as a fitting parameter. (C) 2013 Elsevier B.V. All rights reserved.