Properties and Coagulation Performance of Coagulant Poly-Aluminum-Ferric-Silicate-Chloride in Water and Wastewater Treatment

Abstract

An efficient inorganic polymer coagulant, poly-aluminum-ferric-silicate-chloride (PAFSC), was developed using two approaches: (i) hydroxylation of the mixture of AlCl3, FeCl3 and fresh polysilicic acid in different Al/Fe/Si molar ratios to obtain PAFSCc and (ii) hydroxylated poly-aluminum-iron-chloride (PAFC) combined with aged polysilicic acid in different Al/Fe/Si ratios to produce PAFSCm. The properties of PAFSC in comparison with polyaluminum silicate chloride (PASC) and polyferric silicate chloride (PAFC) were characterized by various experimental methods. The effect of Al/Fe/Si molar ratio on the hydrolysis-polymerization process of Al (III) and Fe (III) in PAFSC solutions was examined by pH titration, and the effect of Al/Fe/Si molar ratio on electrokinetic mobility of PAFSC was studied by Zeta potential measurement. The laboratory experiments were performed to evaluate the PAFSC in comparison with polyaluminum chloride (PAC) for the coagulation of synthetic water samples, actual surface water and wastewater. The results show that interactions exist among aluminum species, ferric species and polysilicic acid, and the Al/Fe/Si molar ratio affects the Zeta potential of the hydrolyzate and the coagulating performance. PAFSC achieved a better water treatment result than PAC. At the same basicity (B) value and Al/Fe/Si ratio, PAFSCc has better coagulation performance than PAFSCm. PAFSC is a new type and high efficiency composite inorganic polymer coagulant.