Characterization and phosphorus removal of poly-silicic-ferric coagulant

An inorganic polymer, poly-silicic-ferric (PSF) coagulant was prepared by co-polymerization, and the hydrolysis products distribution of PSF was calculated from the pH changes during the hydrolysis process of PSF. The characterization of PSF and total phosphorus (TP) removal by PSF were studied in comparison with that of polyferric aluminum (PFA). The results revealed that PSF has more than 30% TP removal than PFA. The optimal metal/phosphorus molar ratio of TP removal by PSF is from 0.6 to 1.2 for the synthetic water and from 1 to 2 for the sewage water, respectively. PSF has higher TP removal at both neutral and higher pH sides from 7 to 12 for the synthetic water and from 7 to 13 for the sewage water, in comparison with PFA which has much higher pH side from 11 to 12 for the synthetic water and from 11 to 13 for the sewage water, respectively. PSF mainly removes TP by complexation or adsorption, in which FePO4 precipitation contributes a little.

The optimal Me/P molar ratio by PSF is from 0.6 to 1.2 and 1 to 2 for the synthetic water and DES4200.3d 6/24/2009 14:24:17 the sewage water, respectively, and PSF has TP removal about 30% higher than PFA at this Me/ P range. PSF shows excellent TP removal at neutral pH side and higher pH side, while PFA has higher TP removal only at much higher pH side. The optimal pH range of TP removal by PSF is from 7 to 12 and 7 to 13 for the synthetic water and the sewage water, respectively, which can be desirable for its use prior to or during the biological treatment. While the optimal pH range of removing TP by PFA is from 11 to 12 and 11 to 13, which is very stringent for water treatment. Complexation or adsorption on solid Fe(OH)3 is the main mechanism of removing phosphorus by PSF, in which the formation of FePO4 precip3– itants by Fe3+ and PO4 contributes a little. The removal of TP mainly depends on the characteristics of coagulants which are different from various coagulants.. The particular characteristics of PSF is just one of the important reasons for which PSF has excellent TP removal. Acknowledgments This research was supported by a financial from National Program on Key Basic Research Projects (973 Program, China) (No. 2004CB418500)