Study On Preparation Of Polymeric Aluminum Ferric Chloride Sulfate Coagulant From Circulating Fluidized Bed Fly Ash

Abstract Circulating fluidized bed fly ash is a new type of solid waste of Circulating fluidized bed boilerburning fuels such as coal gangue and desulfuration inside the furnace; the ash includes fly ash and slag.Because of large differences, the utilization rate of CFB in China is less than30%; most of the CFB isstacked in the open-air repository. Ash’s stacking not only occupy the land, pollute the environment, butalso there are potential safety hazard and waste of resources. Make good use of CFB ash has social benefits,economic benefits and other combined revenues.The study is focused on the comprehensive utilization of fly ash by the coal gangue power plant in Fuxin;a polymeric aluminum ferric chloride sulfate （PAFCS） flocculants was prepared by the process of acidleaching, hydrolysis, polymerization, aging, etc. In order to realize the useful components of the CFB ashwas efficient-clean-utilization. The main points are as follows:（1） The results showed that the CFB ash is accord with the characteristics of high silica, low aluminum,high-sodium, low calcium and magnesium, and contain TiO2and P2O5generally, from coal gangue inFuxin; the mainly composition is amorphous state which has good activity of silica-alumina; the particlesize is most of12μm; the ash are disperse and irregular particles without fixed shape.（2） The optimum conditions were obtained: concentration of hydrochloric acid6mol/L, temperature ofacid leaching is110℃, time of acid leaching is120minutes, ratio of liquid to solid is4:1, addition amountof KF is25wt%, and the leaching rates of Fe₂O₃and Al₂O₃are92.7%and59.46%.（3） The kinetics equation of acid leaching process of Fe₂O₃and Al₂O₃can be described by1-（1-α）1/3=k′t.the acid leaching process of Al₂O₃conforms to the typical “shrinking unreacted core model”, and theapparent reaction order is1.0875，the activation energy of the reaction is21.186kJ/mol，while the processspeed rate is controlled by the diffusion and chemical reaction rate. The acid heating and leaching processof Fe₂O₃conforms to the typical “core shrinking model of reaction” in a certain time, the apparent reactionorder is0.9992，the activation energy of the reaction is42.063kJ/mol，while the process speed rate iscontrolled by the chemical reaction rate.（4） The result shows that in the temperature of80⁸5℃the raw acid leaching solution of CFB ash isneutralized with Al（OH）₃to the pH of3³.5, heat preservation time is2hours, SO₄^2-and PO₄^3-ions arebrought in later stage of heat preservation. Aged at room temperature after24hours, than liquid sample ofred-brown has been produced. Solution can be kept more than three months at room temperature. Theflocculating ability of PAFCS is better than poly aluminum chloride （PAC） under the same conditions.