MODELING CD ADSORPTION IN SINGLE AND BINARY ADSORBENT (PAC) SYSTEMS

Adsorption of cadmium by two powdered activated carbons (PAC) is investigated in single and binary adsorbent systems. Both PACs are effective in removing cadmium from solution. Cadmium adsorption increased with increased solution pH. The surface complex formation (SCF) model, a surface-solution chemical equilibrium model, successfully simulated the individual pH-adsorption edges. Cadmium adsorption decreased with increased cadmium surface loading. This phenomenon was attributed to the surface sites having a range of binding energies. Reflecting this phenomenon, several of the complexation constants decreased with the cadmium/carbon ratio. The SCF model successfully simulated the cadmium surface loading versus soluble cadmium curves for the entire range of cadmium and carbon concentrations studied when the cadmium-carbon complexation constants are modified to account for their variation with the cadmium/carbon ratio. Cadmium adsorption in the binary PAC system was observed to follow ideal behavior. The SCF model, using complexation constants determined from single PAC experiments, successfully predicted cadmium removal from solution.