Preparation Of APT And Thermal Decomposition To Prepare WO 3 By External Field Assisted Neutralization Crystallization

Ammonium paratungstate(APT)is an important intermediate product in the process of tungsten metallurgy.It is the main raw material for the production of tungsten products such as tungsten powder and tungsten carbide powder.The purity and crystal properties such as morphology,grain size and fluidity greatly affect the subsequent tungsten products of all aspects of performance,so the morphology and particle size control of ammonium tungstate is a key step in the tungsten metallurgy process.At present,industrial production is mainly used in the preparation of APT by evaporation crystallization method.The operation is convenient and the production capacity is large,but the product has the disadvantages of large particle size,poor appearance and large energy consumption.It is difficult to meet the requirements of ultrafine tungsten products.Although fine APT can be prepared at room temperature by neutralization crystallization method,but the morphology of APT is poor and the process takes a long time.Therefore,in order to prepare APT with uniform morphology,small average particle size,uniform particle size and good dispersibility,this paper studied the preparation of APT by microwave and ultrasonic dual field co-neutralization crystallization method,and explored the effect of various reaction conditions on product performance,and the products prepared under the optimum conditions were characterized.At the same time,a new method for preparing WO3 by microwave heating calcined APT was explored.The main work of this paper and the main achievements are as follows:(1)The effects of preparation method,heating method,ammonium tungstate concentration,solution pH value,crystallization temperature,ultrasonic mode,crystallization reaction time,microwave and ultrasonic combined power,aging time on the morphology and grain size of APT were discussed that preparation by microwave and ultrasonic assisted co-neutralization crystallization method.Experimental results show: The morphology of APT prepared by microwave and ultrasonic synergetic mode was significantly better than the morphology of APT that prepared by conventional heating and single microwave heating;The rectangular box column single crystal APT was obtained via neutralization crystallization method assisted by microwave with ultrasonic.The preparation conditions were optimized as 275 g·L-1 ammonium tungstate concentration,pH value 7,95 ?reaction temperature,15 min reaction time,700 W microwave power,1000 W ultrasonic power,1: 2 ultrasonic mode and 0 minute ageing time.The ammonium paratungstate prepared under the optimum conditions was characterized,the results show that the morphology of the crystal particles is smooth and the particle size distribution is between 1.6 and 12.2 ?m,the average particle size is 5.8 ?m,and the dispersity is good.XRD shows that the crystalline particles are pentasodium monovate tannonite with pentahedral monoclinic structure,and the crystallinity is high and the crystal form is complete.Differential thermal-thermogravimetric analysis shows that ammonium pentahydrate can be completely decomposed after 450 ?.(2)The effects of calcination conditions such as microwave power,calcination temperature and holding time on the morphology and particle size of WO3 were investigated by microwave heating calcination of APT,at the same time,the final product WO3 was analyzed by XRD,morphology and particle size.Experimental results show: At the microwave power of 800 W and the calcination temperature of 600 ?,the decomposition of APT was carried out without the need of thermal insulation,and the WO3 particles with regular morphology and uniform size;10 g of ammonium paratungstate can be completely decomposed in 12 minutes by microwave heating calcination,calcination time can be greatly shortened compared with the traditional methods;XRD results showed that WO3 crystals were complete and the crystallinity was high;The WO3 prepared under the optimum calcination inherited the good morphology of ammonium paratungstate,the average particle size of WO3 is about 6 ?m,which is little change compared with the particle size of ammonium paratungstate.