| Our country is in the middle stage of industrialization,industrial development has produced a certain degree of influence on the environment,the production of industrial waste increased environmental burden.Fly ash is a bulk solid waste produced by the existing energy supply mode.It contains a variety of trace heavy metals,and a large amount of accumulation has a bad effect on the atmosphere,soil and water environment.Fly ash is rich in aluminum elements.After extraction,flocculants and other products can be prepared to reduce the consumption of bauxite and other resources.In addition,fluorine is widely used in industrial production as an additive,and a large number of industrial wastes thus become the carrier of fluorine,providing the source basis for the diffusion and enrichment of fluorine,and aggravating the pollution of fluorine to local water sources.Drinking high fluoride water for a long time will do great harm to people’s health.Coagulation-precipitation method is recognized as an effective defluorination technology,but the traditional flocculants have low defluorination efficiency for groundwater(low temperature and low turbidity),so it is necessary to develop an efficient compound flocculant for the characteristics of high fluoride groundwater.Therefore,the research provides a new solution for the "reduction" of fly ash and the purification of high fluorine groundwater.The research content includes the extraction of aluminum elements from fly ash(CFA)and the preparation of PSAF from aluminum containing liquid as raw materials,and the evaluation and exploration of the efficiency of fluoride removal.Extraction of aluminum from fly ash by alkali melting roasting-acid leaching method.Na OH and fly ash were calcined at high temperature to obtain the corresponding product,and then the aluminum leaching test was carried out with sulfuric acid solution.The factor levels in roasting process and acid leaching process were optimized by orthogonal test.The results showed that the extraction rate of aluminum reached 86% when roasting temperature was 700 ℃,m(Na OH):m(CFA)=1.2,roasting time =30 min,leaching temperature =60 ℃,leaching time =50min.In addition,the mechanism of roasting activation was explored.A series of reactions took place at high temperature with Na OH and CFA,which made mullite and quartz in fly ash convert to nepheline and zeolite easily soluble in acid,effectively improving the extraction rate of aluminum.Finally,the model fitting of the leaching kinetics of aluminum was carried out,and the leaching kinetics equation and the apparent activation energy of the reaction were obtained,which provided an important reference for further strengthening the leaching process and improving the economic index.Polysilicate aluminum iron flocculant was prepared from aluminum acid liquid.In order to improve the defluorination rate,the single-factor test was conducted to preliminarily study the effects of dosage of flocculant,preparation conditions n(Al):n(Fe),alkalization degree and polymerization temperature,and 1.8 mmo/L was determined as the optimal dosage.On this basis,the central experimental design(CCD)in response surface optimization method(RSM)was used to optimize the preparation conditions,and a reliable regression model was obtained.The optimized preparation conditions were as follows: n(Al): n(Fe)= 7.62 : 2.38,degree of alkalinity=0.36,polymerization temperature =35 ℃,under these conditions,the removal rate of fluoride reached 84.48%.PSAF was characterized by XRD,FTIR and other techniques.The results showed that PSAF was a polymeric amorphous polymer.Al and Fe reacted with silicic acid to form a new substance.In addition,its distribution pattern was explored.Ferron time by time complexation colorimetric method shows that transitional intermediate polynuclear hydroxyl complexes and macromolecular hydroxyl complexes are the main active substances.The flocculation performance of PSAF was compared with that of commercial flocculants.The results showed that the prepared PSAF had good defluorination and dephosphorization effect,the generated alum was dense,the settling speed was fast,it had high use value,and could reduce the residual aluminum in effluent.At the same time,the feasible process flow is designed and the production cost of PSAF is estimated.The results show that it has high economic benefits.Finally,the mechanism of fluoride removal was discussed,among which surface adsorption,electric neutralization,complexation,flocculation bridging and net sweeping were the main methods of fluoride removal.In conclusion,compared with traditional flocculant PAC,PSAF has great advantages in fluoride and phosphorus removal,with better energy efficiency ratio. |
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