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Divalent and trivalent ion exchange with zeolite A.

The ion-exchange isotherm for Ca2+ exchange with sodium zeolite A was determined at 25 OC by using a novel solid uptake analytical scheme and a Langmuir adsorption model, resulting in an improved value for the thermodynamic equilibrium constant. Ion-exchange isotherms and approximate thermodynamic equilibrium constants were also determined for calcium zeolite A exchange with Pb2+, Cd2+, and Cu2+. Pb2+ and Cd2+ exchanges were found to be reversible, whereas Cu2+ exchange was not, probably due to Cu(OH),(s) precipitation upon or within the zeolite. Ion exchange was attempted but found to be irreversible with C$+, Hg2+, Fe3+, and A13+. Except for Cr3+, these ions caused zeolite A structure degradation, probably through extensive proton exchange. Cr3+ exchanged partially and then formed a precipitate. Data obtained in this work provide an improved understanding of the possible environmental water effects of zeolite A.