Surface Area and Exchange Capacity Relation in a Florida Kaolinite

In connection with the study of certain properties of clay‐water systems, an investigation was made of the exchange behavior‐surface area relations of a series of controlled particle‐size (monodisperse) fractions of a domestic kaolin. Surface areas were estimated by application of the Brunauer‐Emmett‐Teller theory to low‐temperature nitrogen adsorption isotherms. Similar estimates were made based on room‐temperature water adsorption isotherms. Exchange behavior was studied using direct quantitative techniques involving the exchange of divalent manganese. Good correlation was found to exist between the computed Brunauer‐Emmett‐Teller areas and the exchange capacities over the particle‐size range 10 to 0.05 μ, equivalent spherical diameter. These results suggest that the exchange behavior in kaolinites is primarily a surface phenomenon and does not depend on isomorphous substitutions.