Transport coefficients and cadmium salt rejection in nanofiltration membrane

Cadmium is one of the main toxic pollutants generated by industrial activities. Many methods have been used to remove cadmium from wastewater issued from these industries. In the present study removal of cadmium Cd(II) ions from aqueous streams was investigated through a nanofiltration membrane process. The retention was studied as a function of the counter-ions, the ionic force and pH. The transport through the TFCS membrane was described by irreversible thermodynamics. The well-known Speigler-Kedem model was applied in order to deter-mine phenomenological parameters σ and Ps respectively, the reflection coefficient of the membrane and the solute permeability of ions. The convective and diffusive parts of the mass transfer were quantified.

When treating a salt solution with a TFCS NF membrane, it was shown that the sodium salts retention sequence is R(Na2SO4) > R(NaCl) > R(CdCl2) and cadmium salts R(CdSO4) > R(CdCl2) > R(CdNO3)2. The data indicate that the membrane is negatively charged, and the Donnan exclusion mechanism seems to play an important role. We have used the Speigler-Kedem model. The results of the application of this model show that there was a good agreement between theoretical and experimental curves. Phenomenological parameters σ and Ps were calculated. They depend highly on the type of anion of the electrolyte solute. We concluded also, that the rejection of cadmium and flux depends on the pH. The results show that the NF is a very promising method of the treatment of acidic stream charged with cadmium.