Impact of Al³⁺ Concentration on Montmorillonite Sedimentation: Insights Into Particle Size Behavior

Particle size is crucial for sedimentation processes. However, there is limited research on how varying particle sizes influence the sedimentation of fine-grained particles. This study examined the aggregation behavior of two types of montmorillonite particles with different sizes under different concentrations of Al³⁺. The findings indicated that the sample of fine particles exhibited a more rapid reduction in turbidity and a greater increase in the absolute value of surface potential across various Al³⁺ concentrations. Despite this, both samples achieved comparable final supernatant turbidity, sediment layer height, and residual particle size, suggesting that the enhancing effect of Al³⁺ on the sedimentation of fine-grained montmorillonite is limited by particle size. Different concentrations of Al³⁺ result in the formation of hydroxyl compounds and hydroxides that adsorb onto mineral surfaces, promoting the sedimentation of finer-grained montmorillonite in the sample of fine particles. DLVO theory confirmed that the electrical double layers of the samples of coarse and fine particles gradually diminished under the influence of Al³⁺, effectively enhancing the aggregation of montmorillonite. Furthermore, thermodynamic analysis suggested that particles smaller than 500 nm do not settle further, even with the addition of aluminum ions.