Sorption of Valine on Montmorillonite

The publications on amino acid adsorption on clay minerals before 1974 are summarized in the book by Theng (1974). It provides information on the adsorbed quantity of different amino acids on cation-exchange montmorillonites and the characteristic IR bands of amino acid-montmorillonites adsorption compounds. Usually, only the adsorbed quantity of amino acids on montmorillonites is shown, and no adsorption mechanism is usually hypothetized (e.g., Friebele et al. 1981 Rak and Tarasevich 1982), except in Stadler and Schindler (1993a) where the adsorption is evaluated by the surface-complexation model, and the possible surface complexes are given for p-alanine. 

the adsorption of valine on different cation-exchanged montmorillonites is described (Nagy and Konya 2004). A discussion of the kinds of interactions that are possible in the ternary system of montmorillonite/valine/metal ions will be presented, and a description how the metal ions can affect these interactions. The interlayer cations (calcium, zinc, copper ions) were chosen on the basis of the stability constants of their complexes with valine. The adsorption of valine on montmorillonite is interpreted using a surface-complexation model. 

When studying the sorption of amino acids, their reactions in the solution and on the interface have to be taken into account. In aqueous solution similar to EDTA (Section 2.8.1), these are the protonation and complex-formation reactions. The protonation reactions of valine are as follows  

K s are the stability constants of the protonated valine species (Table 2.11). 

The Stability Products of Calcium-, Zinc-, and Copper-Valine Complexes and Protonated Forms (Burger 1990) 

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