Characterization and coagulation of a polyaluminum chloride (PAC) coagulant with high Al13 content

A polyaluminum chloride (PAC) coagulant was prepared from AlCl3·6H2O and Na2CO3. The Al13 species in PAC was separated and purified by the SO 4 2 − / Ba 2 + deposition-replacement method, and characterized by 27Al-NMR and XRD. From 27Al-NMR spectroscopy, it was found that PAC obtained after separation and purification contained more Al13 (PAC–Al13, for short) than original PAC before separation and purification. In XRD spectra, a strong Al13 signal appeared in the range of 2θ from 5 to 25°. Jar tests were performed to test the coagulation efficiency of AlCl3, PAC and PAC–Al13 in treating synthetic or actual water samples. Compared with PAC and AlCl3, PAC–Al13 gives the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. Under the study conditions, PAC–Al13 gave about 90% humic acid removal and almost 100% reactive blue dye removal when its dosages were 4.0 and 15 mg/L as Al, respectively. The Al13 species has a higher positive charge and is the most effective polymeric Al species in water and wastewater treatment.