Exchange isotherms, divalent cations

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. 

The transformation of the equilibrium (or selectivity) constants and the ion-exchange isotherms can easily be made only for homovalent ion exchange because the ion-exchange isotherms usually do not take into consideration the heterovalent character of the ion exchange. This causes additional serious problems in the evaluation of isotherm parameters. It is shown for the exchange of monovalent and divalent cations that... 

Cation Exchange in Mordenite. Until 1974 there had been few systematic studies of ion exchange in mordenite and only Rees had determined isotherms. Peculiarities were found which had not been observed in A, X, and Y zeolites or in chabazite, in that only limited exchange of divalent ions could be achieved. Using a natural mordenite from Harbourville, Nova Scotia, Rees found for... 

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