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-based IPF without any toxic problems is greatly expected. In this paper, a new protocol for preparation of iron-based IPF is investigated. Three kinds of silica, named silicaA, silicaB and silicaC, are prepared and used as modifiers to tailor-make polyferric silicate (PFSi), denoted PFSiA. PFSiB and PFSiC, respectively, in accordance to the above silica. Based on several direct and indirect speciation methods, the species distribution and characteristic of three kinds of PFSi are investigated in detail. The experiment results show that the species distribution of PFSi is mainly decided by the kinds of silica introduced and Si/Fe ratio adopted. SilicaA and silicaB function as precipitation preventing reagents during the hydrolysis of Fe(III). At certain amount of basicity, Fe(a) (monomers) increases with increase of Si, Fe ratio, while Fe(c) (colloidal species) decreases markedly. Although the formation of Fe(c) is inhibited, the stabilization of Fe(b) (oligomers or polymers) can still not be achieved. SilicaC on the other hand exhibits little effect on the species distribution of modified Fe(III) solutions. The coagulation behavior of above PFSi is also examined. The different effect of silica is then discussed with respect to the chemical species.