抄録
Several commonly used adsorption isotherms were applied to phosphate adsorption data for 24 different complexes of hydroxyaluminum (HyA) or hydroxyaluminosilicate (HAS) ions with montmorillonite (Mt) or vermiculite (Vt) clays. The applied isotherms were evaluated with regards to their goodness of fit utilizing different criteria adopted by several earlier workers for this purpose. Relative merits and limitations of those criteria were discussed on statistical ground. The isotherm equations were found to describe the phosphate adsorption data with different levels of success. The two surface Langmuir equation was found to be the best in describing the adsorption data suggesting the existence of two different populations of adsorption sites on the HyA/HAS-Mt/Vt complexes that have varying affinities for phosphate ions. The OH or OH2 groups coordinated with Al atoms at the broken edges of HyA or HAS polymers fixed on the external planner surfaces, and/or in the interlayer spaces of Mt/Vt were assumed to be predominantly involved in the ligand exchange reaction of phosphate adsorption in Region I. Ligand exchange predominantly with OH groups linking Al atoms inside the polymeric structure of the fixed HyA or HAS ions was assumed to be the principal adsorption process in Region II. The Temkin equation, however, was almost equally successful which was followed by the Freundlich equation in terms of their goodness of fit. The estimated adsorption parameters of different equations fitted were although numerically different but were positively and significantly correlated with each other at 1% level of significance suggesting that these parameters are relevant to describe phosphate adsorption behavior of the complexes as well as possess wide confidence limits.
