Estimation of solid phase activity coefficients for non-ideal cation exchange behaviour in laboratory samples of UK Triassic sandstones

Abstract

AbstractA traditional laboratory method for measuring cation exchange parameters was applied to plugs of Triassic sandstone core. The objective of the study was to measure cation exchange capacities and selectivity coefficients in the Ca—Mg−Na—K system in intact rock samples, and to investigate the extent to which the system departs from ideality. The method involved the use of NH4Cl as a high ionic strength exchange salt solution in column experiments. Non-ideal behaviour was observed, being most obvious for the K—Na, K—Mg and K—Ca exchange systems. Activity coefficients for the exchanger phase were estimated and a dependence on the composition of the exchanger was recognized. An equation for exchange equilibria is proposed where this dependence is accounted for in the form of a power function.