THERMODYNAMICS AND THERMOCHEMISTRY OF CATION EXCHANGE IN CHABAZITE

A quantitative study has been made of the exchange of Li+, K+, Rb+, Cs+, Ag+, Tl+, NH4 +, Ca2+, Sr2+, Ba2+ and Pb2+ with Na+ in a natural chabazite. All the ions except Cs+ exchanged almost completely with Na+. From the isotherm contours, Kielland plots and differential heat curves attempts have been made to determine cation positions in the zeolite. For the ions that exchange almost completely the thermodynamic affinity sequence, based on the standard free energies of exchange, is Tl+ > K+ > Ag+ > Rb+ > NH4 + > Pb2+ > Na+ = Ba2+ > Sr2+ > Ca2+ > Li+. Heats of exchange were determined calorimetrically and were negative when K+, Rb+, Cs+, Ag+, Tl+ and NH4 + in the zeolite, and positive when Na+ was replaced by Li+, Ba2+ and Pb2+. Exchanges involving Ca2+ and Sr2+ were so slow that it was not possible to determine equilibrium heats of exchange. © 1969.