Influence of Sodium and Lithium Monovalent Cations on Dispersivity of Clay Soil

Abstract

Exchangeable sodium ions are widely reported to be the principal reason for the dispersivity of soils. From fundamental theoretical considerations, several other factors such as pH, cation exchange capacity, mineralogy, electrolyte concentration, and dissolved salts can affect the attractive/repulsive forces in soils and hence are considered to have a significant role in assessing the dispersivity of soils. To assess the influence of these parameters, a known dispersive soil was treated with sodium hydroxide and lithium hydroxide and the dispersivity was assessed. It was confirmed that the effects of these factors on dispersivity are manifested through the amount of hydration of the adsorbed monovalent cations. Because the inner hydration shell of adsorbed monovalent cations is larger than those of higher-valency ions, dispersivity is related to the presence of monovalent cations alone. It was also established that within the monovalent cations, the size of hydrated ions can vary and can influence the dispersivity of the soil. The dispersivity of soils increased with a reduction in the size of the ions. The increase in repulsive force (causing dispersion) due to the reduction in the size of the cation is explained through diffuse double layer theory. A complete philosophy of dispersion is proposed in light of the current experimental results.