On methods to measure cation exchange capacity and amounts of leached cations of bentonites

Abstract

Cation exchange capacity (CEC) and amounts of leached cations (LC) of bentonite were used to predict the water permeability and swelling property in researches related to bentonite buffer for radioactive waste disposal project. The purpose of this study is to examine various methods of measuring CEC and LC of bentonites and to propose proper method depending on bentonite types. Three methods using respectively ammonium acetate, barium chloride and ben-zyltrimethylammonium chloride (BTM) to obtain CEC or LC or both were examined. The following conclusions are obtained: i) CEC obtained by the improved method using barium chloride is generally in agreement with by the method using ammonium acetate; ii) Summation of LC measured by the method using BTM generally agrees with CEC meas-ured by the method using ammonium acetate; iii) Method using BTM can reduce the effect of calcium carbonate dis-solution, which is often a problem for other two methods; iv) Summation of LC measured by the method using BTM may be regarded as CEC.