Thermodynamics of Sodium-Copper Exchange on Wyoming Bentonite at 298 K

The exchange of copper (Cu/sup 2 +/) for sodium (Na/sup +/) at 298/sup 0/K on Wyoming bentonite was investigated in a perchlorate background medium maintained at pH 5.0 to 6.0 and at a total normality of 0.01N. It was found that the exchange process could be well characterized by a Vanselow selectivity coefficient that was equal to 1.32, independent of the exchanger composition, and by a similarly constant apparent adsorbed metal charge equal to 0.92 +/- 0.05 eq kg/sup -1/. These results are in conflict with previous data obtained at 295/sup 0/K for Na/sup +/-Cu/sup 2 +/ exchange on montmorillonite in a 0.01N chloride background medium. It was concluded that a principal cause for the differences between the two sets of data could be the presence of CuCl/sup +/ complexes in the chloride medium.