Study On The Effect Of Alumina,Calcium Oxide And Silicon Oxide On The Preparation Of Zinc Ferrite

In this paper,zinc ferrite was prepared from pure minerals zinc oxide and iron oxide by high-temperature roasting method.The reaction behavior of zinc-iron ore and the influence of alumina,calcium oxide and silica impurities on the formation of zinc ferrite were studied by XRD analysis,SEM analysis and BET analysis.The effects of reactant ratio,activate time,calcinate temperature and calcinate time on the content and physical properties of the products were investigated.Thermodynamic analysis and verification were carried out.The main conclusions are as follows:(1)In the reaction of zinc oxide,iron oxide and alumina mixture,alumina reacted with zinc oxide preferentially to produce zinc aluminate.Activate time and calcinate time had little effect on the formation of zinc ferrite and aluminium ferrite and aluminium ferrite.The best activate time for facilitating the reaction and maximize the product of zinc ferrite were 60 minutes,the best calcinate time were 120 minutes,respectively.(2)Calcinate temperature was the main factor affecting the reaction of mixture and product character in the reaction of mixture of zinc oxide,iron oxide and alumina.When the calcinate temperature was more than 850?,alumina converted into ferric aluminate and zinc aluminate,and resulted in reducing production of zinc ferrite.The largest amount of zinc ferrite produced at 750?.In addition,the particle size of the product was less than 3?m,and the particle was spherical,ellipsoid or irregular,and the surface of the particle was smooth and a little agglomeration,when the calcinate temperature was 750??850? and the calcinate time was 120 min.The BET specific surface area of calcined product was 49.43 m2·g-1,total pore volume was 0.12m3·g-1,average pore diameter was 9.54nm,under the conditions of molar ratio of ZnO,Fe2O3 and Al2O3 of 1:1:1,activate time of 60 min,calcinate temperature of 750? and calcinate time of 120 min.(3)The Gibbs free energy was negative in the temperature range of 600??1000? in the reaction of zinc oxide,iron oxide and alumina mixture.The Gibbs free energy of FeAl2O4 was the smallest,the Gibbs free energy of ZnAl2O4 was the second,and the Gibbs free energy of ZnFe2O4 was the largest.Some FeAl2O4 formed when calcinate temperature reached 950?,due to a small amount of Fe2O3 was decomposed into FeO at high temperature,and FeAl2O4 was first formed.(4)The ratio of reactants,activate time and roasting time had little influence on the reaction,and the roasting temperature had a great influence on the reaction in the roasting process of the mixture of zinc oxide,iron oxide and calcium oxide.There were better crystallinity,smooth particle surface and uniform particle size,when products prepared at molar ratio of ZnO,Fe2O3 and CaO of 1:1:1,activate time of 60 min,calcinate time of 120 min and calcinate temperature of 750?.The BET specific surface area of the products was 59.69m2·g-1,total pore volume was 0.08m3·g-1,average pore diameter was 5.11 nm.(5)Calcium oxide had obvious hindrance effect on the formation of zinc ferrite,in the roasting process of the mixture of zinc oxide,iron oxide and calcium oxide.Calcium oxide reacted with iron oxide to form calcium ferrite first,and zinc ferrite could not be completely roasted with Fe2O3.(6)Thermodynamic analysis showed that the Gibbs free energy of CaFe2O4 formation was significantly less than that of ZnFe2O4,so CaO will give priority to the complete reaction in the theoretical process.At the same time,with the increase of calcination temperature,the Gibbs free energy of zinc ferrite formation decreases and the reaction proceeds more favourably,which was conswastent with the actual reaction results.(7)In the process of calcination of zinc oxide,iron oxide and silicon oxide,the change of silicon oxide content did no affect the formation of zinc ferrite.The change of activate time had little effect on the formation of zinc ferrite,because of the stable structure and properties of silica.Calcinate temperature was important factors affecting the formation of zinc ferrite,and a largest amount of zinc ferrite produced by calcination at 750?.The calcination time had little effect on the formation of zinc ferrite from the mixture,and largest the amount of zinc ferrite at 120 min.(8)When the molar ratio of zinc oxide,iron oxide and silicon oxide mixture was 1:1:1,activate time was 60 min,calcinate time was 120 min and calcinate temperature was 750°C,the particle size of zinc ferrite was uniform and the morphology was good,and pore size was mainly 10-50nm,the BET specific surface area was 72.33 m2·g-1,the total pore volume was 0.34 m3·g-1 and the average pore size was 17.95 nm.In summary,the effects of impurity minerals such as alumina,calcium oxide and silicon oxide on the preparation of zinc ferrite by calcination of zinc oxide and iron oxide in pure mineral system were studied in thwas paper.The effects of three impurity minerals on the formation of zinc ferrite and the characterwastics of mineral phade transformation were expounded,which would provide a baswas for further study of mineral phade transformation of iron cap ores in zinc sulfide ore deposits,and provided a theoretical foundation for the new technology of preparing zinc ferrite.