Separation And Purification Of Si-Ti Alloy And Clean Utilization Of Titanium-containing Blast Furnace Slag And Silicon Waste

Aiming at the bottleneck problem of high impurity,low usage and low amount of Si-Ti alloy obtained by silicon reduction of Ti-bearing blast furnace slag,and the key problem of low removal rate of oxygen impurity in diamond wire saw silicon kerf(silicon waste).The separation and purification of Si-Ti alloys was used to combine the cleaning and utilization of silicon waste and Ti-bearing blast furnace slag with the purification process of low-purity silicon.The Si-Ti alloy extracted from Ti-bearing blast furnace slag by strong reducibility of low-purity silicon/silicon waste.The most important and difficult oxygen impurities in the silicon waste were removed by using the oxide slag produced by Ti-bearing blast furnace slag,the high purity silicon and eutectic Si-Ti alloy materials were obtained by physical separation(electromagnetic directional crystallization)of the Si-Ti alloys for the first time,and the high purity silicon and TiO₂,were obtained by chemical separation of the above Si-Ti alloys for the first time too.(1)Si as a reducing agent,the reduction rate of TiO₂in Ti-bearing blast furnace slag is99.5%,which is the highest reported value;(2)When the reaction temperature is not less than 4 h at 1773 K,the reduction rate of TiO₂in Ti-bearing blast furnace slag by silicon reduction does not change much(96.8%),that is,the equilibrium time of TiO₂in Ti-bearing blast furnace slag is 4 h at 1773;(3)Reaction temperature(heat preservation temperature)is 1723 K,the reduction rate of silicon to the TiO₂in Ti-bearing blast furnace slag is only 75.83%.At 1773 K,the reduction rate of silicon to titanium blast furnace slag is 96.8%.Increasing the reaction temperature(heat preservation temperature)has no obvious effect on the reduction rate of TiO₂;(4)When the content of Al₂O₃and Ca O is increased in the slag containing titanium blast furnace,TiO₂the highest reduction rate did not change significantly,the maximum values were 96.2%and 96.7%.An increase of MgO content in slag has the most obvious effect on the reduction rate of titanium in titanium-bearing blast furnace slag(99.1%);(5)Although the amount of reducing agent(mass ratio of titanium blast furnace slag to industrial silicon)has an effect on the reduction rate of titanium in titanium blast furnace slag,the fluctuation is small(the reduction rate is 98.4-99.5%when the mass ratio of slag to silicon is 1:1-1:0.4)Separating Si and Ti in the Si-Ti alloy by physical method(Electromagnetic directional crystallization),a new approach was proposed to prepare multi-products,high-purity Si powders,bulk Si,and Si/TiSi₂materials(eutectic Si-Ti),simultaneously using inexpensive low-purity Si(99.3%)and metallurgical waste(Ti-bearing blast furnace slag).TiO₂in Ti-bearing blast furnace slag was first reduced by Si to form a Si-Ti alloy which was then separated into high-purity bulk Si(99.97%)and Si/TiSi₂materials(99.4%)using directional solidification.The bulk Si could be repeatedly recycled as a reductant,or further upgraded to prepare super-pure Si powders(99.995%)after acid leaching.Separating Si and Ti in the Si-Ti alloy by chemical method(wet method),a novel approach is proposed to simultaneously extract Ti from Ti-bearing blast furnace slag to prepare TiO₂and recycle Si from diamond wire saw silicon kerf to prepare high-purity Si.Firstly,diamond wire saw silicon kerf(86.9%Si)was employed as a reductant to extract Ti from Ti-bearing blast furnace slag to prepare bulk Si-Ti alloys,and the largest extraction rate was 99.4%.Secondly,Si and Ti in the bulk Si-Ti alloy were separated using a HF-containing acid solution.Ti in the Si-Ti alloy dissolved into the HF-containing acid solution,and high-purity Si was obtained after acid leaching.The purity of Si in diamond wire saw silicon kerf increased from 86.9%to 99.94%.Thereafter,a Na OH solution was used to precipitate Ti(OH)₄from the HF-containing acid solution,and TiO₂(81.7wt%)was prepared by roasting Ti(OH)₄.Notably,the new approach had the advantage of concurrently eliminating impurities while recycling diamond wire saw silicon kerf.Finally,Na OH and HF solutions were used to prepare high-purity Na F(>98%)to treat the waste solutions.The results of this study provides a new and sustainable technology for clean utilization of diamond wire saw silicon kerf and Ti-bearing blast furnace slag.Preparation of high-purity silicon powder and TiO₂from Si-Ti alloy by combining physical method(Electromagnetic directional crystallization)and chemical method(wet method);Firstly,The impurity in the Si-Ti alloy was removed by physical method(Electromagnetic directional crystallization);and then,the eutectic Si-Ti(Si/TiSi₂)alloy after impurity removal was separated by chemical method(wet method)to prepare high purity silicon and TiO₂.Thereafter,a NH₄OH solution was used to precipitate Ti(OH)₄from the HF-containing acid solution,and TiO₂was prepared by roasting Ti(OH)₄at 1373K temperature(99.5 wt%).Since the eutectic Si-Ti(Si/TiSi₂)alloy is obtained by silicon reduction Si-Ti electromagnetically oriented crystallization,the impurity content in the eutectic Si-Ti alloy decreases significantly compared with that in the silicon reduction alloy.Such as,Fe11000ppmw,Mn6000ppmw in the Si-Ti alloy,and Fe138ppmw,Mn136ppmw in eutectic Si-Ti(Si/TiSi₂)alloy.