EXCHANGE PROPERTIES OF HYDROGEN IONS IN CLAYS

This paper reports results from a thermodynamic and thermochemical study on the exchange reactions between hydrogen ions and sodium or ammonium ions in a montmorillonite clay. A calculation of the free energy of exchange shows that substitution of sodium by hydrogen ions is an exergonic process, while the reverse is true for the substitution of ammonium by hydrogen ions. Direct calorimetric measurements of the heat of exchange show that substitution of the sodium by the hydrogen ion is an exothermic process and again the reverse is true for the substitution of ammonium by hydrogen ions. The values of free energy and enthalpy of exchange both indicate that in the sequence of affinity for the clay surface, the hydronium ion is closer to sodium than to ammonium. /Author/