Keywords: adsorption models, adsorption optimisation, heterogeneous model, surface coverage, solute dissociation constants, weak electrolytes, activated carbon
Influence of solute dissociation constants on the optimum adsorption of weak electrolytes on activated carbons
The pH of solutions has dramatic effects on the adsorption capacity of activated carbons from solutions, while the adsorption curves for weak electrolytes acquired as a function of pH show maxima at some intermediate pH. This intermediate pH is usually near the pKa of the electrolyte. Some apparent controversy inherent in these statements has, however, motivated experimental and analytical investigation of these systems. The present investigation therefore employed standard ASTM techniques in the study of adsorption systems, as well as non-linear least squares regression techniques to predict adsorption on activated carbon. It was observed that the adsorption isotherms do not indicate the existence of clear adsorption maxima for pKa values above 10. The existence of both a maximum as well as a minimum on the adsorption of a range of moderately weak electrolytes is indicated. Good agreement was observed between experimental and predicted adsorption isotherms.