Research On The Formation Mechanism And Purification Process Of By-product Micro-silica Powder In The Process Of Industrial Silicon Production

Silica fume is a by-product obtained by the dust collection device during the production of metallurgical grade silicon or ferrosilicon alloy.Because of its high specific surface area and high activity,it has become an important "industrial additive".However,due to the high content of impurities in silica fume,the added value of its utilization is low.Therefore,by studying the formation mechanism of silica fume and removing impurities in a targeted manner,its utilization value and application field will be increased.Dictation technologies,such as XRD,XRF,SEM,EPMA,FIB-TEM and etc.,are used to research the occurrence state and distribution of impurities in the raw materials,and the microstructure,phase composition,product purity of the samples before and after purification.This research studies five aspects: the formation mechanism of silica fume particles,the distribution of impurities,the structure of silica fume,roasting pretreatment and wet acid leaching purification process flow.The results show that during the formation of silica fume,nucleation is the main reason for the formation of very fine particles,while condensation causes its rapid growth,and the change of condensing temperature gradient in the flue causes the silica fume particles to have a specific layered structure.At the same time,by analyzing the FIB-TEM image,it was determined that the inside of silica fume can be divided into impurity regions and silicon dioxide regions,which indicates that there are two processes of the formation of silica fume: the first is the Si O and impurity vapor nucleates homogeneously to form silica particles;the second is the silica particles formed below the material surface escapes through the airway of the material surface,and it condenses out of phase with the volatile components in the carbonaceous reducing agent,forming an impurity region.Additionally,by comparing the carbon removal rate(82.97%)of conventional calcination at 600? for 1 h,microwave removal at 600 ? for 30 min can significantly improve the carbon removal efficiency,which can reach 86.17%.In this paper,the raw material roasted at 900 ?,after it was leaching by HF+HCl mixed acid,and then leaching by high-temperature sulfuric acid at 150? for 4h,the silica purity of the final product is 98.640%.Meanwhile,according to the unique layered structure of silica fume,this paper innovatively compared the purity of silica fume after purification by crushing and unbroken.It was found that the purity of silica fume reached 99.042% after the destruction of the layered structure,which was 2.857% higher than the content of silica in the raw material,and compared with the unbroken purification efficiency increased by 0.402%.To determine the distribution of the internal layer structure and impurities of the micro-silica powder,which provides a theoretical basis for the subsequent improvement of the purity of silica fume.By optimizing silica fume acid leaching process,a new process of silica fume acid leaching purification with high efficiency and low energy consumption is obtained,which provides the reliable basis for the preparation of preparing high-purity silica.It will greatly improve the added value of silica fume and improve the utilization rate of solid waste.