Preparation Of Flocculant Polysilicate Aluminium Ferrric From Fly Ash And Its Application In Wastewater Treatment

Fly ash is a solid waste discharged by coal-fired power plants and coal-fired boilers, veryyear one hundred million tons of fly ash piled up in our country caused great impact on theenvironment. The waste utilization use of fly ash, turning waste into treasure, has far-reachingsignificance in land conservation and environmental protection. In recent years, more andmore fly ash in wastewater treatment and research, and has made certain achievements,forming a Virtuous cycle of waste by waste. In this paper, preparation of flocculantpolysilicate aluminium ferric was prepared to deal with the life waste water, using fly ash asmajor raw material, can be achieved the purposes of waste treatment waste andcomprehensive utilization of resources.（1） The product-flocculant polysilicate aluminium ferric was prepared through roasting,acid leaching and the aging three process to the fly ash.Putting Aluminum, Iron ion leaching rate as the indicator, analyzing the solubilizationeffect of the cosolvent NaF and Na₂CO₃, selected Na₂CO₃as cosolvent because it makealuminum and iron leaching condition better. The best proportion of Na₂CO₃/SiO2molar ratiowas0.5, the solubilization effect was optimal, the Al³⁺and Fe³⁺leaching rate were37.65%and53.20%respectively.Putting light transmission rate of the life waste water as indicators, designing L16（4⁵）orthogonal experiment to optimize the process of roasting, acid leaching stage and L9（34）orthogonal experiment to optimize the process of aging stage, then worked out the optimumprocess conditions of the preparation of flocculant polysilicate aluminium ferric by fly ash.The optimum prosses conditions of the preparation of flocculant polysilicate aluminium ferric by fly ash was worked out, that calcination temperature is860℃, m （Na₂CO₃）: m （fly ash） is0.2, and the acid leaching temperature is105℃, the hydrochloric acid concentration is30%,concentration dissolution time is1.5h, the pH of leaching solution is5.0, the ripening time is24h, the aging temperature is25℃, the amount of ferric chloride added is2g. At this time, thetransmittance of the processing wastewater is best to87.36%.（2） Through level of single factor experiment, respectively changed the four conditions ofthe flocculant amount, wastewater pH, wastewater temperature, flocculation time to examinethe removal results of the water quality parameters （including chemical oxygen demand（COD）, color, total nitrogen, total phosphorus, ammonia） by flocculant polysilicate aluminiumferric dealing with. Under optimum conditions, the wastewater being treated by the flocculantCOD removal rate reached81.12%, color removal rate reached94.89%, total nitrogenremoval rate reached33.09%, total phosphorus removal rate94.12%, ammonia removal ratereached44.29%.（3） By comparing the removal results of water quality parameters （chemical oxygendemand （COD）, colordegrees, total nitrogen, total phosphorus, ammonia）of commerciallyavailable flocculant polyaluminum cloride （PAC）, polyferric chloride （PFC） and homemadeflocculant polysilicate aluminium ferric （PAFSi）, reached conclusion that homemadeflocculant performance is better than the commercially available flocculants.（4） Using infrared spectroscopy and scanning electron microscopy （SEM） test methods,the structure morphology of polysilicate aluminum ferric were studied. The structureconfirmed that in the PFASi molecular part of the aluminum ions, iron ions and the hydrolysisof complex aluminum ions, iron ions chelated with the coexistence polysilicate （complexed）to the reaction generating iron-aluminum-silicon polymer. The morphology confirmed thatPFASi overall had a three-dimensional, porous, overlapping and extending structuralcharacteristics. Due to such structural features, increasing the surface area and adsorptioncapacity of PAFSi, therefore PFASi showed excellent flocculation ability.