Modified inorganic polymer flocculant-PFSi: Its preparation, characterization and coagulation behavior

As a new kind of water and wastewater treatment reagents, inorganic polymer flocculants (IPFs) are in a trend of rapid development. Among them, iron-b ased IPF without any toxic problems is greatly expected. In this paper, a n ew protocol for preparation of iron-based IPF is investigated. Three kinds of silica, named silicaA, silicaB and silicaC, are prepared and used as mod ifiers to tailor-make polyferric silicate (PFSi), denoted PFSiA, PFSiB and PFSiC, respectively, in accordance to the above silica. Based on several di rect and indirect speciation methods, the species distribution and characte ristic of three kinds of PFSi are investigated in detail. The experiment re sults show that the species distribution of PFSi is mainly decided by the k inds of silica introduced and Si/Fe ratio adopted. SilicaA and silicaB func tion as precipitation preventing reagents during the hydrolysis of Fc(Ill). At certain amount of basicity, Fe. (monomers) increases with increase of S i/Fe ratio, while Fe, (colloidal species) decreases markedly. Although the formation of Fe, is inhibited, the stabilization Of Feb (oligomers or polym ers) can still not be achieved. SilicaC on the other hand exhibits little e ffect on the species distribution of modified Fe(III) solutions. The coagul ation behavior of above PFSi is also examined, The different effect of sili ca is then discussed with respect to the chemical species. (C) 2001 Elsevie r Science Ltd. All rights reserved.