Effect of surfactant and PAM on the settlement of kaolinite particles and its mechanism analysis

High concentrations of fine-grained clay minerals in tailings water are highly detrimental to environmental protection and water recycling. Using kaolinite as the study subject, this research investigates the effects of various cationic surfactants (DDA, DTAB, TTAB, CTAB) and flocculants (APAM, NPAM, CPAM) on the sedimentation of kaolinite particles. The study explores the impact of single agents, combined agents, and the sequence of their addition on kaolinite particle sedimentation. The results indicate that when using individual agents at low concentrations, CTAB outperforms TTAB, DTAB, and DDA, while APAM is more effective than NPAM and CPAM. The optimal performance is achieved with a CTAB concentration of 2×10^-4 mol/L and an APAM dosage of 20 mg/L. When combining agents, the best results are observed when CTAB is added before APAM. By fixing the APAM dosage at 20 mg/L and varying the CTAB concentration, the highest sedimentation rate and lowest turbidity are obtained at a CTAB concentration of 1.5×10^-4 mol/L. Mechanistic insights were obtained through aggregate imaging, area measurement, zeta potential testing, and contact angle testing. Cationic surfactants alter the surface properties of particles, reducing surface electronegativity and increasing hydrophobicity, which diminishes inter-particle repulsion and promotes aggregation, thereby reducing turbidity. Flocculants form larger flocs through adsorption and bridging, accelerating the sedimentation process. When flocculants and cationic surfactants are used together, the resulting flocs are more stable and larger, with an average floc area reaching 5017.6079 µm², indicating a significant reduction in fine particles within the solution.