Study On The Use Of High Iron Fly Ash As A Coagulant

With the deepening of industrialization and urbanization,the pressure of population,resources and environment is increasing,and the problem of water pollution in China is becoming more and more serious.The problem of urban sewage plays an important role in modern society.Fly ash is mainly from the emissions of coal-fired power plants.Its quantity is huge and its output increases year by year.It can be modified into substances with properties such as coagulation and adsorption,which has a good prospect in the treatment of pollutants in water and can achieve the effect of treating waste with waste.In this study,high iron fly ash was used as raw material to remove COD from campus domestic wastewater,and the high iron fly ash was sorted into magnetic and non-magnetic fly ash,and the non-magnetic fly ash was modified with chemical reagents to produce coagulant for reducing COD index in campus domestic wastewater.The coagulant with the best effect was selected by comparison,and then mixed with magnetic fly ash to explore the best coagulation and adsorption conditions.The experimental results showed that.(1)Translated with www.Deep L.com/Translator(free version)In acid modification(AFA),the best preparation conditions of coagulant are as follows:2mol/ L sulfuric acid solution is mixed with fly ash(solid-liquid ratio is 1:3),1g Na Cl is added,and the coagulant prepared is stirred continuously for 30 min in a constant temperature water bath at 25℃ at a speed of 80 r/min.The coagulant has the best coagulation performance in acid modification.At this time,the COD removal rate of the prepared coagulant reached 64% of sewage.(2)In alkali modification(BFA),the optimal preparation conditions of coagulant are as follows:When 2mol/L sodium hydroxide solution is mixed with fly ash(solid-liquid ratio is 1:3)and stirred continuously for 30 min in a constant temperature water bath at a speed of 80 r/min at 50℃,the COD removal rate of the coagulant prepared at this time reaches 37% of the sewage on the basis of this coagulant.(3)Through the analysis of SEM,BET and FTIR infrared spectra,the reasons for the difference in the removal rates of the two were explored,and the modification mechanism was analyzed:Through comparison,it is found that the surface of AFA is rougher,with higher degree of corrosion and more obvious porous structure.Due to BFA,it can be seen from FTIR infrared spectrum that the characteristic peak strength of Si-O bond and Al-O bond of FHA and BFA is significantly weakened.This indicates that after modification,the Si-O bond and Al-O bond in the original fly ash are broken,leading to the decrease of the response value and the red shift of different degrees,which is also the reason why AFA has stronger coagulant adsorption capacity.And through the coagulation adsorption test,the adsorption capacity of the three is AFA > BFA > FA.(4)The optimal conditions for magnetic coagulant treatment of campus sewage are as follows:Fe-AFA was obtained by mixing 10 g AFA with 3g magnetic powder to treat 100 m L campus domestic sewage.When the p H value of sewage was 7,after mixing and stirring for 15 min,centrifugation and static for 24 h,the COD value of the supernatant was 49.23mg/L,and the effluent water quality could reach Grade A standard.According to the SEM figure,the magnetic flocs on the surface of Fe-AFA are more than the magnetic flocs adsorbed on the surface of Fe-BFA,and the adsorption capacity of the three flocs is Fe-AFA > Fe-BFA > FA through the coagulation adsorption test.After magnetic fly ash is added,the coagulation mechanism also plays a role on it.The addition of magnetic fly ash increases the reaction crystal nucleus and improves the removal efficiency of COD in water;the second is that after the magnetic flocs are formed,the specific gravity is larger,which accelerates the sedimentation rate of the flocs and greatly reduces the time from turbidity state to clarification state.