The adsorption of valine on cation-exchanged montmorillonites

The interfacial reaction of valine was systematically studied on the surface of different cation-exchanged montmorillonites, namely calcium-, copper-, zinc-montmorillonite, and montmorillonite KSF. The exchanged cations were selected on the basis of stability of their valine complexes. At first the interfacial acid/base properties of cation exchanged montmorillonites were studied: the stability constants of the ion exchange processes on the layer charges were determined by radioisotopic labeling, the edge charges were studied by potentiometric titration and surface complexation model. sorption was studied as a function of valine concentration, pH and time. The results were evaluated by a surface complexation model and the possible surface complexes and their stability products were given. The results show what kind of interactions are possible in the ternary system of montmorillonite/valine/metal ions and how the metal ions can effect on these interactions. The assumed processes are: (1) the adsorption of valine in the interlayer space, where valine is adsorbed in protonated form, (2) the adsorption of valine on the protonated aluminol sites, and (3) the adsorption of positively charged complexes on the deprotonated silanol sites, if the exchangeable cation forms a positive complex with valine. The total amount of the adsorbed valine and the ratio of the different adsorption processes is determined by the affinity of metal ions to the layer charges and by the stability of the metal ion–valine complexes in solution.