Predictive evaluation of ion-exchange selectivity on a titanium antimonate cation exchanger

Ion-exchange selectivity has been investigated for exchange of divalent transition-metal and rare-earth-metal ions with hydrogen ions on titanium antimonate cation exchangers. A specific selectivity feature was found for this exchanger through the Kielland and Langmuir plots. The Langmuir equation has been derived from the Kielland plot of the ion exchange, and the Langmuir constant was found to be dependent upon the total ion concentration. Plots of the corrected selectivity coefficients, KMH, on the logarithmic scale vs. the equivalent fraction of metal ions in the exchanger, text-decoration:overlineXM, showed a break point at text-decoration:overlineXM= 0.01–0.02 for the divalent metal ions and at text-decoration:overlineXM= 0.005 for the rare-earth-metal ions. This behaviour can be interpreted assuming a two-site model. One site available at infinitesimal text-decoration:overlineXM value has a high steric limitation. The Kielland coefficients, Cm, were found to be in the range –190 to –1.1 for the divalent metal ions and –110 to –17 for the rare-earth-metal ions. The distribution coefficients, Kd, at an infinitesimal exchange, text-decoration:overlineXM= 0, were evaluated.

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