Study On Chlorination Process And Kinetics Of High Alumina Coal Fly Ash

Coal fly ash,as a type of solid waste with a large stock,has always been an urgent problem in environmental governance.High alumina coal fly ash is a type of coal fly ash with an alumina content above 40%found in China.Adopting a reasonable process route to extract alumina from high-alumina coal fly ash has always been the focus of resource recycling,and it can also alleviate the problem of lack of bauxite resources and the need for large imports in China.In view of the problems of low extraction rate of aluminum,large amount of secondary slag,and difficult disposal of waste slag in the current methods of extracting alumina from high alumina coal fly ash,this paper proposes the method of using carbon chlorination to achieve the extraction and utilization of alumina and silicon oxide in coal fly ash.Through the mineralogy analysis of coal fly ash,the chemical composition,mineral phase composition,microstructure,grain size and density of coal fly ash are obtained.The thermodynamic analysis of the carbochlorination system of coal fly ash was carried out.The difference between the boiling chlorination of coal fly ash and the chlorination of the pellet was compared by single factor experiment The slag and product were characterized.Kinetic studies were carried out on the chlorination process of alumina and silica.The following conclusions were obtained:(1)In the boiling chlorination experiment of coal fly ash,due to the poor physical properties of coal fly ash,the fluidized state of coal fly ash is poor in the fluidized bed state,and the gas-solid two phases cannot be fully contacted.Currently,boiling is used.The method of chlorination has a low degree of reaction,so that polyvinyl alcohol is used as a binder to pre-form pellet pulverization of coal fly ash and coking coal.(2)The optimum single-factor conditions for pellet chlorination were temperature 950℃,reaction time 1h,chlorine partial pressure 101.3 kPa,carbon distribution 27 wt%,and chlorine gas flow rate 0.3 L.min.The chlorination ratio of alumina is 81.2%,and the chlorination ratio of silicon oxide can also be 60%or more.Finally,chemical composition analysis and XRD and SEM analysis of the slag showed that the main phase in the slag was an intermediate product of mullite,and the surface of the smooth pellet was corroded by chlorine gas to become loose and porous.The slag can continue to be carbon chlorinated,so that the degree of chlorination is further improved,and finally the full utilization of coal fly ash is achieved,The product was characterized,and the product was different at different condensation positions.As the temperature of the condensation zone decreased and contact with air,the product gradually transitioned from AlCl3 to AlCl3·6H2O.(3)The chlorination process kinetics experiments show that the chlorination process of fly ash conforms to the unreacted core model without solid product formation.At 850～950℃,both alumina and silica are controlled by chemical reactions.The apparent activation energies of the two chlorination reactions were 65.70 kJ/mol and 89.06 kJ/mol,respectively,and the reaction order of the chlorination reaction and the kinetic equations with temperature and partial pressure of chlorine were obtained.