Effects of temperature on the stability of colloidal montmorillonite particles at different pH and ionic strength

The effect of temperature at different pH and ionic strengths on the aggregation kinetics of colloidal montmorillonite particles in aqueous dispersions was investigated. For a given temperature and pH, the rate constant for aggregation increased with increasing ionic strength. At pH ≤ 4 the rate constant for colloid aggregation increased with increasing temperature, regardless of ionic strength. At pH ≥ 10 the aggregation rate constant decreased with increasing temperature as a general trend. In the intermediate pH interval, the aggregation rate constant apparently decreased with increasing temperature except at the highest ionic strength, where it increased with increasing temperature. The aggregation rate constant decreased at alkaline pH compared with the acidic pH range. This effect became more pronounced at higher ionic strengths and higher temperatures but could not be observed at 4 °C. These observations are in qualitative agreement with DLVO calculations taking temperature, pH and ionic strength into account.