Modified Poly Silicate Ferric With Magnesium(PSiFM): Preparation, Characterization And Coagulation Behavior

It has been proved that one of the most important steps in the water andwastewater treatment process is coagulation, which is used for thedestabilization of colloidal suspensions as well as the removal of suspendedsolids and dissolved natural organic matters. Nearly all the colloids found innatural waters carry negative charges and thus they remain in suspension dueto the mutual electric repulsion. Flocculation process can remove theseimpurities.Poly silicate ferric magnesium is a new promising inorganic polymerflocculants （IPFs）, prepared by poly silicate （PSiA） and traditional metal saltcoagulant, which could have optimized synergistic effect of chargeneutralization and sweep coagulation, in addition the treated water has noresidual of iron color left.The auto polymerisation of Fe（Ⅲ） in water will produce a wide range ofFe species, including Fe³⁺、Fe（OH）₂⁺、Fe（OH）²⁺、Fe（OH）₃、Fe（OH）₄^-，Fe4₂（OH）₂⁴⁺、Fe₃（OH）₄⁵⁺, which developed an effect of charge neutrality.Magnesium has a great activity and adsorption ability, non-corrosive,non-toxic, safe, and harmless, which is known as the "environmentallyfriendly" green chemical for water treatment. It has a good bleaching effect onthe sewage. In addition, the introduction of magnesium can also counteract thecolor residue of iron based coagulant. PSiA consists of silica tetrahedrons which are linked by silicon-oxygen-silicon bonds. The auto polymerisation ofsilicic acid will produce a wide range of silica species, including dimeric（Si₂O₃（OH）₄）^2-, trimeric （Si₃O₅（OH）₅）^3-, tetrameric （Si₄O₈（OH）₄）^4-andeventually polymeric species. The main goals of adding such a modifier are toincrease the molecular size and enhance the aggregating ability of thecoagulant. Specific results are as follows:1. Modified poly silicate ferric with magnesium （PSiFM） was preparedusing the composite-poly method in this paper. With the compare of thechemical oxygen demand （CODCr） reduction, the optimum flocculation effectcould be obtained when the viscosity of polysilicic acid （PSiA） was1.4×10-3Pa·s. It has a great influence of the Si/Fe mole ratio on the nature ofproduct, the best option of Si/Fe, Mg/Fe mole ratio was around1.2. The prepared coagulant with optimized condition was characterized interms of major typical properties, such as IR, SEM etc, as it’s shown thatPSiFM has a structure to the benefit of flocculation.3. the change of pH, conductivity, and CODCrremove ratio （of products）were also investigated indicating PSiFM has a super effect than the flocculantwithout Mg, poly silicate ferric （PSiF）.4. Finally, the coagulation behavior of PSiFM was assessed by studyingthe reduction of chemical oxygen demand （CODCr） and suspended solids （SS）in the diatomite model suspensions and actual water sample, which removeratio attained80%and90%, respectively. The obtained results suggested thatthe coagulation performance of PFSiM was more superior than the otheriron-based coagulants.This paper has been studied the coagulant of PSiFM, which has a bettertreatment performance in treating with the diatomite model suspensions andan actual water sample of Yuan Dadu river water in Beijing. It provided thebasic data of the products used in water treatment for further study offlocculent. It will have a better economic and social benefit in introducing this flocculant into water treatment.