Baseline studies of the clay minerals society source clays: Cation exchange capacity measurements by the ammonia-electrode method

The cation exchange capacity (CEC) of fine-grained materials, and especially clay minerals, is a fundamental property of these materials, and can be determined routinely. A search of the recent literature illustrates the great interest of this property to researchers. For example, a search of the GeoRef database for references to “cation exchange capacity” for the years 1980 to 1999 yields 2559 citations. Methods of measurement are based on a determination of the quantity of a particular exchangeable cation, by a variety of means, expressed per 100 g of dry clay. These methods are principally chemical and spectroscopic. The present study describes the results of measurements made primarily on Source Clay minerals using a particularly simple, reliable and inexpensive method developed by Busenberg and Clemency (1973). The method, in common with other procedures, involves the saturation of exchangeable cation sites with a chemical species, in the present case, ammonium cations. The ammonium-exchanged clay is dispersed in an alkaline solution of sodium hydroxide that releases the ammonium as dissolved ammonia gas. A specific-ion electrode then detects the signal from the ammonia dissolved in solution. Comparison of the signal from the unknown solution with a series of solutions containing known concentrations of ammonia yields the ammonia …