Determining pseudo-equilibrium of montmorillonite colloids in generation and sedimentation experiments as a function of ionic strength, cationic form, and elevation

Colloid generation and sedimentation experiments were carried out on Na- and Ca-montmorillonite in order to verify whether pseudo-equilibrium concentrations are reached at the same level in both types of experiments. The size and concentration of colloidal Na- and Ca-montmorillonite particles were monitored as a function of time and distance from the colloid bed in different ionic strength solutions. A stable pseudo-equilibrium concentration was reached after time in generation and sedimentation experiments. The colloid concentration decreased sharply at distances near to the colloid source. Na-montmorillonite concentration at pseudo-equilibrium (roughly quantified at distances ⩾7 cm from the colloid source) was 5.2 ± 0.5, 0.5 ± 0.1, and 0.2 ± 0.1 mg L−1 in 0.001, 0.01, and 0.1 M NaCl solution, respectively, while the Ca-montmorillonite concentration was 0.4 ± 0.2 mg L−1 in 0.001 M NaCl.

The size distribution of montmorillonite colloidal particles reaches pseudo-equilibrium over time. Similar pseudo-equilibrium profiles are reached by generation and sedimentation experiments.Figure optionsDownload as PowerPoint slide