The objective of this work is to
characterize the kinetics of Donnan
dialysis process by a simple model. The Nernst–Planck equation
is simplified by neglecting the membrane swelling pressure and assuming
an average diffusion coefficient for all ions. Experimental data are
presented on the permeation of monovalent phosphate ions from a KH2PO4/NaH2PO4 feed solution
to a NaCl receiver solution using two different anion exchange membranes:
a low flux membrane (Fumasep FAB) and a high flux membrane (Selemion
AMV). Measurements indicate a brief initial ion exchange process in
which the membrane is loaded with phosphate ions. Phosphate transport
data fit the predicted correlations and provide values of the overall
kinetic coefficient. The kinetic coefficients derived from both membranes
were found to increase linearly with the membrane phosphate concentration.
The phosphate dialysis data of the low flux membrane were found to
be controlled by a diffusive process, while the data of the high flux
membrane were found to be mass transfer controlled. The increase of
the kinetic coefficient with phosphate concentration is shown to be
related to the increase in membrane ion diffusivity with its solution
concentration.
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