Development of Cation Exchange Processes in Geosynthetic Clay Liners

An investigation was conducted to systematically analyze the cation exchange characteristics of a conventional GCL as a function of time and concentration of hydration liquid under typical laboratory conditions. GCL specimens were hydrated using DI water and 2 mM, 50 mM, and 200 mM CaCl2 solutions for 4 and 8 h, and 1, 2, 4, 8, 16, and 32 days. Significant and rapid variations occurred in the amount and relative proportions of the bound cations in the exchange complex of the bentonite for the relatively high concentration solutions (50 mM and 200 mM CaCl2). The exchange complex was relatively unaffected in the tests with DI water and 2 mM CaCl2 solution. The highest changes occurred in the Na+ and Ca2+ fractions with relatively low changes in K+ and Mg2+. The majority of the exchange processes were completed within days (approximately <= 8 days) at the high concentration hydration conditions.