Critical Coagulation Concentrations of Sodium and Potassium Illite as Affected by pH

Abstract

AbstractThe effects of saturating cation (Na or K) and pH on the critical coagulation concentrations (CCCs) of illite were measured. Flocculation series tests showed that between pH 6 and 11, the time‐invariant CCCs of Na illite increased from 6 to 58 mol Na m−3; release of interlayer K was controlled by adding 0.1 mol K m−3 to Na‐illite suspensions. The CCCs of K illite increased from 3 to 14 mol K m−3 over the pH range 6 to 10. The lower CCCs of K illite relative to Na illite were consistent with a higher surface affinity for K. Increasing CCC with increasing pH was explained by charge alterations on the edge surfaces due to surface‐specific proton interactions. A comparison of our Na‐illite CCCs to published Na‐kaolinite and Na‐montmorillonite CCCs revealed a greater pH dependence for Na‐illite and Na‐kaolinite CCCs.