Study On The Preparation Of Hydrated Silicon Dioxide From Blast Furnace Slag By Hydrothermal Method

In recent years,with the increasing of China's steel production capacity,blast furnace slag as the main by-product of blast furnace iron production is also increasing.At present,the industrial use of blast furnace slag in China is mainly based on the use of traditional low-tech,which makes its economic value reduced.In order to study the high value utilization of the blast furnace slag.Some scholars used blast furnace slag as raw materials to prepare high value-added fine chemical products.But the method of preparation of hydrated silicon dioxide using hydrothermal method to digest blast furnace slag has not been reported.Therefore,in this paper,the blast furnace slag was used as raw material,and the precursor of hydrated sodium aluminosilicate was prepared by hydrothermal method to digest the blast furnace slag,then the silicon dioxide was prepared by adjusting the pH of hydrated sodium silicate solution.The research aims to provide the research foundation for comprehensive utilization of blast furnace slag.The main innovations and achievements are as follows:In this paper,the changes of the vitreous content in the blast furnace slag with the law of time were studied using the blast furnace slag as the research object,which provide the theoretical basis for the comprehensive utilization of blast furnace slag.The influence of various factors on the reaction was studied by using the silicon element in blast furnace slag as the target component.The analysis of thermodynamic and kinetic during the hydrothermal reaction of blast furnace slag,which not only reveales the alkali-soluble behavior of the blast furnace slag and the control mechanism of the target component,but also achieves the efficient separation of target component and blast furnace slag.The mechanism of silica precipitation during pH adjusting process was analyzed,which provided the theoretical basis for precipitation of hydrated silica.The chemical composition and characteristics of blast furnace slag and the variation of vitreous content in blast furnace slag with time were studied.The results shows that the mass coefficient K is 1.89,the coefficient of water is 1.98,the activity coefficient is 0.51,the alkaline coefficient is 0.97,which belongs to acid blast furnace slag with good quality,good influence and high activity.The XRD analysis showed that the vitreous content in fresh blast furnace slag was 97.6%,and the content of vitreous body was linear with the time of stacking.The vitreous content in blast furnace slag was linearly reduced with the stacking time.The products were characterized and analyzed by X-ray diffraction,Fouriertransform infrared spectroscopy,thermogravimetry and transmission electron microscopy.The results show that the products are irregular amorphous hydrated silica powder with the particle size distribution between 50 and 100 nm.The indexes of products meet the requirements of the standard HG/T3061-1999.The effects of different conditions on the conversion of SiO₂ were studied,and the thermodynamics and kinetics were analyzed during the hydrothermal reaction of blast furnace slag.The results show that increasing the concentration of NaOH can significantly improve the dissolution of blast furnace slag.The appropriate reaction conditions were as follows: the reaction temperature was 130 ?,the concentration of sodium hydroxide was 3.0 mol·L-1 the ratio of alkali to slag was 0.8,the reaction time was 4 h,and the conversion of silica was 84.3%.The results of orthogonal experiments show that the degree of influences of the four teachnical conditions on the convesion of SiO₂ was in order of concentration of sodium hydroxide>alkali treatment temperature>ratio of alkali to slag>reaction time.The most significant factor was the concentration of sodium hydroxide.The hydrothermal reaction of blast furnace slag can be described by a interface reaction model,and the relationship between the conversion of SiO₂ and reaction time can be expressed as1-3?1-x?2/3+2?1-x?=k1"t.According to the Arrhenius Equation,the apparent activation energy of leaching SiO₂ was 20.13 kJ·mol-1.The effects of different condition on the purity of SiO₂ were studied and the mechanism of the precipitation of hydrated silica was analyzed in the acid hydrolysis process.The results show that the polymerization process of hydrated silica is relate to its concentration and pH value.The optimum reaction conditions were as follows:he reaction temperature was 65 ?,the concentration of hydrochloric acid was 2.0mol·L-1,the acceleration of hydrochloric acid was 0.3 mL·min-1,the pH was 8.5 and the aging time was 2 h,the purity of silica was 96.8%.The results of orthogonal experiments show that the influence degree of each factor on the purity of SiO₂ was in the order of the final pH>the reaction temperature>the concentrations of HCl>add speed of HCl>reaction time.The most significant factor was the final pH.A preliminary exploration of the treatment of alkali residue and solution waste were carried out to provide a process for the preparation of gypsum,aluminum silicate and magnesium aluminum spinel.The main innovation points: researched the variation of vitreous content of blast furnace slag with time using blast furnace slag as the object.The influence of kinetics,thermodynamics and the related factors on the hydrothermal reaction of blast furnace slag was studied systematically,and which can reveal the intrinsic mechanism of the target fraction of alkali dissolution.