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Temperature Effects on Exchange Reactions of Amberlite IR-120 with Calcium, Magnesium, Potassium, and Sodium in Mixtures and Cationic Composition of Resin-Treated Milk

Milk and Food Research, Robert A. Taft Sanitary Engineering Center, Cincinnati, Ohio

ABSTRACT

To prepare charging solutions for regenerating resin at high temperatures, in the process of removing cationic radionuclides from milk, temperature dependence on ion-exchange equilibria was studied. The resin in the H⁺ form was equilibrated with the solution containing Ca, Mg, K, and Na at 26, 62.8, 68.3, 73.8, and 76.7 C. From the analysis of resin and composition of the charging solution, the apparent equilibrium constants, free energy charge (??F), enthalpy change (??H), entropy change (??S), and heat capacity change (??Cp) were computed for the exchange reactions K vs. Ca, K vs. Mg, K vs. Na, Na vs. Ca, Na vs. Mg, and Ca vs. Mg. Except for reactions K vs. Ca (??Cp = –15.4) and Ca vs. Mg (??Cp = –11.3), the ??Cp for all other reactions was positive and quite large. When ??Cp was assumed to be constant, a linear relationship was found between ??H and T and ??S and log T. Values of ??H in most cases were small. A large, positive ??S was observed with unidivalent ion-exchange reactions. One possible explanation for the increased selectivity of Ca over that of K may be due to increased ion pair formation between potassium and chloride anion.

With the use of apparent equilibrium constants and a predicted mole fraction of cations required on the resin, charging solutions were prepared at 26 and 76.7 C. The cationic composition of milk samples treated with such resins showed no significant difference when compared with the composition of untreated samples.