Flocculation Performance and Interfacial Adsorption Mechanism of Aluminum Hydroxide–Polyacrylamide in Coal Slime Water Treatment

Effective treatment of coal slime water is essential for sustainable coal preparation plant operation but hindered by the stable suspension of fine, negatively charged particles. To address this, a novel star-shaped inorganic-organic hybrid polymer (aluminum hydroxide-polyacrylamide, Al-PAM) was synthesized via in situ polymerization. Its performance was systematically compared with well-established coagulants/flocculants-polyaluminum chloride (PAC), non-ionic polyacrylamide (NPAM), and their binary combination through settling tests and quartz crystal microbalance with dissipation monitoring (QCM-D). The results showed a positive correlation between the molecular weight of Al-PAM and its flocculation efficiency. The optimal variant, Al-PAM-442, achieved an exceptionally high initial settling rate (50.4 m/h) and low supernatant turbidity (45.77 NTU) at an ultralow dosage of 6 mg/L. QCM-D analysis elucidated the mechanism: Al-PAM forms a thick, soft, and irreversibly adsorbed hydrated layer on silica, enabling strong electrostatic anchoring and effective polymer bridging. In contrast, PAC adsorption was reversible, while NPAM formed a thin, compact film with poor bridging capacity. Although the combined PAC/NPAM system showed synergistic performance, it required a significantly higher dosage (70 mg/L). This study demonstrates that the star-shaped Al-PAM architecture successfully integrates charge neutralization and bridging into a single molecule, offering a highly efficient and practical solution for industrial coal slurry dewatering.