Study on Hydration of Illite in K+, Na+, Ca2+, Mg2+, and Al3+ Electrolyte Solutions

The hydration of clay particles in aqueous solutions plays an important role in the scientific and industrial fields. In this study, the hydration properties of fine illite particles in K+, Na+, Ca2+, Mg2+, and Al3+ electrolyte solutions were investigated through the relative viscosity method based on Einstein's viscosity equation. During the experiments, the hydration index (I) was measured using a rheometer to analyze the hydration layers formed on the illite surfaces in different aqueous electrolyte solutions, and it was found that the index I was the highest in Al3+ followed by that in Mg2+, Ca2+, Na2+, and K+ in descending order. It was also observed that the index increased as the electrolyte concentration increased until the solution reached an adsorption equilibrium. When electrolytes were added, the effect of electroviscosity on the calculated value of I became weaker until it could eventually be neglected. Based on these results, we concluded that the electroviscosity should be considered when calculating the hydration index of a suspension of fine charged particles with low conductivity.