Study On Polymerization,its Mechanism And Flocculation Performance Of Novel Nano Inorganic Composite Polymeric Ferric Sulfate

The energy source structure of China,what relies mainly on coal,cannot be changed in the short term.The production of inorganic flocculant polyferric sulfate（PFS）using H₂SO₄ prepared by flue gas dry desulfurization and its downstream product Fe SO₄ as raw materials can realize the high-value recycling of sulfur resources in coal-fired flue gas,which is great significance of the sustainable development of economy.In order to solve poor liquid stability,small molecular weight and poor flocculation performance of PFS,PO₄^3-,polysilicic acid（PSi）and Al³⁺were introduced into the preparation process of PFS respectively to synthesize three kinds of nano inorganic composite flocculants:polyferric phosphate sulfate（PFPS）,polyferric silicate sulfate（PFSiS）and polyferric aluminum phosphate sulfate（PFAPS）.The effects of composite flocculants’preparation conditions on their physicochemical properties and flocculation decolorization ability on hydrophobic dye disperse yellow（DY）,hydrophilic anionic dye reactive turquoise blue（RTB）and hydrophilic cationic dye methylene blue（MB）simulated dye wastewater were studied.The microstructure of three composite flocculants was analyzed,and their polymerization mechanisms were simulated and analyzed using molecular dynamics software.The flocculation effect and mechanism of three composite flocculants and PFS on actual oily wastewater and blast furnace gas washing wastewater were compared and studied.The flocculation effect of PFPS on DY and RTB simulated wastewater is significantly better than that of PFS.The introduction of PO₄^3-can promote the polymerization of PFPS,increase the content of flocculation active components in PFPS and inhibit the formation of electrically neutral Fe-polymer precipitation.Moreover,the Fe-polymer formed by PO₄^3-bridging has more positively charged active sites than the Fe-polymer formed only by OH^-,so that PFPS has better flocculation ability.PFSiS has both the electric neutralization ability of PFS and the adsorption bridging ability of PSi,whose flocculation effect on DY simulated wastewater is obviously better than PFS,and retains part of the flocculation capacity of MB simulated wastewater.The polymerization degree of PSi can affect the flocculation ability of PFSiS by affecting the interaction between Fe-polymer and PSi ion in the polymerization process of PFSiS.PSi with proper polymerization degree can make more long-chain PSi ions in PFSiS,which can combine with multiple Fe-monomers to form polymers,and the Fe-monomers can bridge between different PSi ions,so that PFSiS has both great adsorption bridging ability and sufficient electric neutralization ability.The flocculation effect of PFAPS on DY and RTB simulated wastewater is significantly better than that of PFPS.The introduction of Al³⁺can increase the number of positively charged metal polymers in PFAPS and improve flocculation ability.However,it can also compete with Fe³⁺for OH^-and PO₄^3-in the polymerization system,which is adverse to the formation of Fe-polymers and reduce their stability.In the flocculation process of two kinds of actual wastewater,all the three composite flocculants played the physical action of electric neutralization and adsorption bridging,and did not form a new chemical bond with the pollutants in the wastewater.Among them,PFAPS has the best electric neutralization ability and COD removal effect;the neutralization capacity and the COD removal effect of PFPS are between PFSiS and PFAPS;PFSiS has the best adsorption bridging capacity and turbidity removal effect,but its electric neutralization capacity and COD removal effect are the worst.In summary,three kinds of novel inorganic composite polymeric ferric sulfate were synthesized,which solved the problems of poor stability,low degree of polymerization and poor flocculation perfotmance of traditional polymeric ferric sulfate.And it opens up a new way for the high-value utilization of SO₂ recovered from dry flue gas desulfurization.