Synthesis and Application of a Chitosan-Based AM/AMPS Flocculant for the Flocculation of Kaolinite Suspensions: Experimental and Molecular Dynamics Study

Fine kaolinite particles form stable suspensions that impede solid–liquid separation. A chitosan-based flocculant, CS-g-P(AM-AMPS), was synthesized by ultrasound-assisted graft copolymerization of acrylamide (AM) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) onto chitosan (CS). Physicochemical characterization, batch flocculation tests, and molecular dynamics simulations were conducted with the AM/AMPS copolymer P(AM-AMPS) and polyacrylamide (PAM) as reference polymers. Characterization identified amide and sulfonate groups and a rough, porous dry-state morphology. CS-g-P(AM-AMPS) achieved higher final turbidity removal and produced larger median flocs than both reference polymers under their respective selected conditions, with a maximum removal efficiency of 98.5%. Simulations showed that the grafted polymer had the most negative total polymer-surface interaction energy and the largest interfacial hydrogen-bond population. Its segment distribution combined near-surface enrichment with extension into the adjacent aqueous phase. P(AM-AMPS) produced larger median flocs than PAM but achieved lower removal, showing that aggregate size and clarification followed different rankings. These findings suggest that extensive surface contact coupled with chain extension facilitates particle bridging and floc growth. The combined results identify CS-g-P(AM-AMPS) as an effective flocculant for clarifying kaolinite-bearing water.