THE DISTRIBUTION CONSTANT FOR EXCHANGE OF CALCIUM AND MAGNESIUM IN WYOMING BENTONITE

The distribution constant for exchange of calcium and magnesium ions was determined in Wyoming bentonite suspensions with pH values varying from 3.5 to 9.2. Using a neutral salt to extract the exchangeable cations, the mean value of the distribution constant using ion activities in solution was found to be 1.06 and there was no significant difference in the constant at different pH values. Thus, the presence of Al ions in the acid preparations, the precipitation of hydroxy aluminum polymers on the clay surfaces at intermediate pH values, and the precipitation of excess base in the alkaline region possibly as double hydroxides of Al and Mg or Ca had no significant effect on the exchange distribution of Mg and Ca ions.Under comparable conditions, the ion product (Al) (OH) 3 had the same value in the presence of Ca or Mg. Because of this and the fact that the distribution constant for exchange was approximately 1, the two ions may be considered as a single ionic species for practical purposes in suspensions of Wyoming bentonite.