Thermodynamics of Sodium‐Copper Exchange on Wyoming Bentonite at 298°K

The exchange of copper (Cu 2+ ) for sodium (Na + ) at 298°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 0.01 N . 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 −1 . These results are in conflict with previous data obtained at 295°K for Na + ‐Cu 2+ exchange on montmorillonite in a 0.01 N 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 + complexes in the chloride medium.