Study On Selective Extraction And Application Of Silicon Oxide From Blast Furnace Slag

Iron and steel plants in the smelting pig iron will produce a large number of by-products,that is,blast furnace slag,its huge output in China,about 300 million tons per year,its large accumulation is easy to lead to surrounding water,soil and air pollution,and even easy to cause landslide,debris flow and other safety accidents.The blast furnace slag mainly includes Ca O,SiO₂,Al₂O₃and Mg O.Because of the large amount of blast furnace slag,it needs to consume a lot of energy to deal with it,but also will emit a lot of harmful substances to the environment and human body.Therefore,the efficient treatment and utilization of blast furnace slag to develop high value-added products has become a key problem to be solved in domestic and foreign research.At present,some metal oxides,such as Ca O,Al₂O₃and Mg O are recycled by physical and chemical means.In addition,the blast furnace slag is rich in silicon oxide,and its extraction and reuse is an important development direction to realize the resource utilization of the blast furnace slag.For example,the silicon oxide extracted from the blast furnace slag has a wide range of uses and can be used for the preparation of rubber and adsorbents.The extraction of silicon oxide from furnace slag mainly includes acid treatment method and acid-base combined treatment method.Both methods have their own advantages and disadvantages.The acid treatment of furnace slag is simple to operate and the extracted silicon oxide has higher quality and is widely used,but acid treatment requires a higher concentration of acid solution and will produce a certain amount of waste acid after treatment.The combined acid-base method has many kinds of reagents and complicated operation.Compared with the two treatment methods,acid treatment method is favored because it can simultaneously extract a variety of valuable components from the furnace slag to prepare silicon oxide and the extraction rate is high,so it has a great potential for development.In this paper,the traditional acid treatment method was used to optimize the acid treatment conditions and analyze the microstructure of the products in different stages of the acid treatment process,and the application of the extracted silicon oxide was preliminarily explored.This paper mainly studies the extraction of rich silicon oxide from blast furnace slag by hydrochloric acid treatment,and investigates the technological conditions for the extraction of silicon oxide from blast furnace slag and the effects of acid treatment on the microstructure and properties of the products at different stages.The results are as follows:（1）SiO₂ with purity greater than 98% was prepared.Firstly,the influence of concentration of hydrochloric acid on acid leaching effect was investigated.In order to investigate the influence of concentration of hydrochloric acid on acid leaching effect,0.5-4M hydrochloric acid solution was used to extract Ca,Mg,Al,Fe and other metal elements from blast furnace slag,and the residue with high silica content was obtained.On this basis,the acid leaching time and acid leaching temperature were investigated.In this study,the optimal process parameters were obtained as follows:concentration of hydrochloric acid is 3M,acid leaching temperature is 90℃,acid leaching time is 3 h,under the optimal conditions,the purity of silicon oxide was above 98%.Using X-ray diffraction（XRD）,X-ray fluorescence spectrum（XRF）,N₂adsorption-desorption,infrared spectra（FTIR）characterization methods such as analysis of samples,the results show that under the condition of low concentration and low temperature during the high acid leaching slag can not achieve very good effect on silicon oxide extraction,in along with the increase of the concentration of hydrochloric acid can be avoided by increasing reaction temperature appear to achieve extraction of silica sol phenomenon.The silicon oxide product obtained by acid leaching furnace slag was surface modified with sulfhydryl group and applied to the adsorption of heavy metal lead ions.The saturated adsorption capacity of the product could reach 263.5 mg·g^-1.（2）Preliminary exploration of the microstructure changes of the products in the process of blast furnace slag and acid leaching.Through analytical means such as XRD,XRF and SEM of blast furnace slag and acid leaching product properties were characterized,and the results show that the blast furnace slag itself has a complex network structure,the acid leaching reaction can endanger the stability of the blast furnace slag of 3 D mesh structure,make the main component of the original gehlenite disappear,show that acid Baptist gehlenite in blast furnace slag composition such as acid solution and aluminum for free calcium ions so as to realize the effect of damage to its network structure.The conditions for the dissolution of gehlenite were analyzed,that is,to reach a certain Si-Al ratio.The preliminary exploration showed that the dissolution ability of each metal ion was different in the acid leaching reaction.The oxides of Ca and Mg were dissolved first,and then the oxides of Al were dissolved.After acid leaching,the particle size of blast furnace slag decreases but the particle size and distribution are not uniform.The morphology of the samples before and after acid leaching changes greatly,from the flaky and crumbly structure before acid leaching to the rod-shaped and spherical silica particles after acid leaching.The roughness of the sample changed before and after acid leaching and a few particles with rough surface appeared.In the process of acid treatment of blast furnace slag,its complex three-dimensional network structure is destroyed,because the inorganic reaction between hydrochloric acid and metal oxides in blast furnace slag destroys its original crystalline structure,thus obtaining amorphous silicon oxide product.