Sepiolite cation exchange capacity

Competitive adsorption on sepiolite clay of a monovalent dye (e.g., methyl green or methyl blue) and of the divalent organo-cationic herbicides diquat and paraquat was studied by Rytwo et al. (2002). To evaluate a possible competitive adsorption between the two organic compounds, separate aqueous solutions of each cation were used and adsorption isotherms were obtained. Fig. 8.27 shows the amount of diquat, paraquat, and methyl green adsorbed on sepiolite as a function of total added divalent cation. It may be observed that, when the added amounts were lower than the cation exchange capacity of the sepiolite (O.Mmol kg ), aU cations were completely adsorbed. 

Attapulgite and sepiolite data plot on both sides of the neutral line.. The calculated structural formulas of these two clays are more subject to error than those of the sheet structure clays. As is suggested by their low cation exchange capacity octahedral sheets tend to approach neutrality. The amount of R3+ required to maintain neutrality is less if OH substitues for O2. ... 

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