Synergistic effects of various in situ hydrolyzed aluminum species for the removal of humic acid

Due to the diversity of in situ hydrolyzed aluminum species and discrepancy in the binding sites of humic acid (HA), the mechanisms involved in HA removal were significantly different in inorganic particle removal. Based on the background, the coagulation behavior of in situ and performed hydrolyzed aluminum species for the removal of HA was investigated. For AlCl₃, the maximum HA removal reached at weak acidic conditions, where various in situ hydrolyzed Al species containing Al₁ to Al₂₀ cores with different amounts of water molecules were present. Various Al species could meet the demand for different binding sites and enhance the complexing probability for weak binding sites. Meanwhile, most of the binding sites are occupied by the aluminum ion, which brought about better complexation capacity with the Al species. Therefore, the synergistic effects of various in situ hydrolyzed aluminum species played important roles in the removal of HA. Compared with AlCl₃, preformed Al₁₃ had less efficient in HA removal because the Zeta potential of HA formed by preformed Al₁₃ with uniform Al species increased from negative to positive with increase in Al₁₃ dosage. This study provided new insight into the interaction between HA and various hydrolyzed Al species.