Study On Preparation Of Rutile TiO₂ By Microwave Calcination Of Titanic Aci

TiO₂,as the most dominant titanium product,has a wide range of application fields.Among the four crystalline types of TiO₂,rutile TiO₂ has the best pigment performance and the most stable properties.At present,sulfuric acid method is the main process of TiO₂ production in China,among which calcination of metatitanic acid is the key link to produce rutile TiO₂.However,the traditional rotary kiln calcination has problems such as low thermal efficiency,high energy consumption and unstable product quality.Microwave,as a new green heating method,has the characteristics of fast heating speed and high heating efficiency.In this paper,the thermal decomposition characteristics,microwave calcination and phase transition kinetics of metatitanic acid were carried out to provide a theoretical basis for the preparation of rutile TiO₂ by microwave calcination of metatitanic acid.（1）Thermal decomposition characteristics and kinetics study of metatitanic acid were studied.The thermal decomposition process of metatitanic acid in air atmosphere is divided into three stages:dehydration（26～450℃）,desulfurization（560～830℃）,and crystal transformation（ART）-grain growth（830～1000℃）.The apparent activation energy for the dehydration phase of metatitanic acid is 47.25 kJ/mol,and the kinetic model is consistent with the three-stage reaction model with the mechanism function of g（α）=[（1-α）-2-1]/2,lnA of 15.38 min-1;The apparent activation energy for the desulfurization phase of metatitanic acid is 221.89 kJ/mol,and the kinetic model is consistent with the three-stage reaction model with the mechanism function of g（α）=[（1-α）-2-1]/2,lnA of 29.32 min-1.（2）Response surface optimization of conventional calcination and microwave calcination of metatitanic acid for the preparation of rutile TiO₂ was studied.A quadratic regression model for the conversion of rutile TiO₂ under conventional calcination and microwave calcination conditions was developed using the response surface method,respectively.The effects of calcination temperature,calcination time,sample mass and their interactions on the conversion of rutile TiO₂ were investigated.The results showed that calcination temperature,calcination time and sample mass had significant effects on the conversion of rutile TiO₂ under conventional calcination conditions.Under the optimal process of calcination temperature 1016℃,calcination time 70 min and sample mass 58 g,the predicted conversion was 99.99%,which was similar to the actual conversion（98.34%）.Under microwave calcination conditions,calcination temperature and calcination time have significant effects on the conversion of rutile TiO₂,while the sample mass doesn’t have significant effects on the conversion of rutile TiO₂.The predicted conversion of rutile TiO₂ was 99.91%under the optimal process of calcination temperature 866℃,calcination time 61 min and material volume 58 g,which was similar to the experimental value（99.44%）.Compared with the conventional calcination,the final optimized process condition calcination temperature was reduced by 14.7%,calcination time was shortened by 12.8%,and the sintering phenomenon was significantly improved.Microwave calcination of metatitanate for the preparation of rutile TiO₂ is feasible.（3）The phase transition kinetics and strengthening mechanism of rutile TiO₂ prepared by microwave calcination of TiC-doped metatitanic acid were investigated.Both microwave radiation and TiC doping can effectively lower the phase transition temperature point of ART（450℃）by 600℃.The activation energy of phase transition kinetics in the ART stage of calcination of metatitanic acid calculated by JMAK model is 40.81 kJ/mol,which is only 0.0028-0.43 times of that reported.The analysis of ART strengthening mechanism shows that TiC can play the role of heating inducer,providing calcined crystal seeds and promoting oxygen vacancy generation;microwave radiation can play the role of direct energy supply.