Coagulation characteristics of polyaluminum chlorides PAC-Al30 on humic acid removal from water

Coagulants polyaluminum chlorides with a high Al30 content (PAC-Al30) were prepared in laboratory, and the aluminum hydrolysis ratios (B = [OH−]/[Al3+]) of PAC-Al30 were 1.2, 1.8 and 2.4 respectively. Coagulation behaviors of PAC-Al30 with different B values and conventional coagulant AlCl3 were compared by jar test to remove humic acid (HA) from water. Floc growth, charge neutralization capacity, HA removal and residual aluminum concentration in the purified water were investigated. The influences of initial pH and coagulant dosage on coagulation behaviors were considered. The results show that coagulants PAC-Al30 exhibit much stronger floc formation capacity, have broader effective dosage range and initial pH range, reach higher HA removal efficiency, and get lower residual aluminum concentration than AlCl3 does. The coagulation/flocculation capacity of PAC-Al30 increases with the B value. The HA removal reaches 98.5% at an initial pH of 7.0 and PAC-Al30 (B = 2.4) dosage of 0.16 mmol L−1 (total aluminum concentration, Alt) when the initial HA concentration is 10 mg L−1; the residual aluminum in the purified water is 0.066 mg L−1. Al30 is verified as highly efficient coagulation/flocculation species for HA removal.