Characterization and coagulation of a polyaluminum chloride (PAC) coagulant with high Al 13 content

Abstract

A polyaluminum chloride (PAC) coagulant was prepared from AlCl 3·6H 2O and Na 2CO 3. The Al 13 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 Al 13 (PAC–Al 13, for short) than original PAC before separation and purification. In XRD spectra, a strong Al 13 signal appeared in the range of 2 θ from 5 to 25°. Jar tests were performed to test the coagulation efficiency of AlCl 3, PAC and PAC–Al 13 in treating synthetic or actual water samples. Compared with PAC and AlCl 3, PAC–Al 13 gives the best results for turbidity, humic acid and color removal, and achieves the highest charge-neutralizing ability. Under the study conditions, PAC–Al 13 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 Al 13 species has a higher positive charge and is the most effective polymeric Al species in water and wastewater treatment.