Modeling of the cadmium transport through a bulk liquid membrane

Abstract 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(NO 3 ) 2 solution through BLM (D2EHPA in kerosene) to 1 M H 2 SO 4 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 H 2 SO 4 ≫ c Cd was not required. None of the following: an assumed Cd-D2EHPA complex (CdP 2 (HP) 2 , CdP 2 HP), presence of undimerized D2EHPA in BLM, or ion pair formation Cd 2 + · SO 4 2 - 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.