Study On Extraction Silicon And Aluminum From Coal Gangue By Supercritical (Subcritical) Hydrothermal Activation Combined With Hydrochloric Leaching

In recent years,supercritical fluid technology has a good prospect which has been widely used in extraction separation,chemical reaction engineering,environmental protection,material science and so on.Coal gangue is a solid waste discharged during the processes of coal mining and coal washing.In this paper,supercritical fluid technology is applied to activate solid waste against the background of preparation of silica and alumina from coal gangue.The reaction characteristics of coal gangue activation in supercritical（subcritical）hydrothermal and the effects of supercritical water activation conditions on the dissolution rates of silicon and aluminum were investigated.Compared with the traditional activation method of coal gangue,the supercritical（subcritical）water activation technology has the advantages of low reaction temperature,cheap chemical reaction medium and environmentally friendly.Based on these advantages,a new process of the extraction of silicon and aluminum by activated coal gangue by supercritical（subcritical）hydrothermal combined with acid leaching is proposed.Five kinds of coal gangue were selected as experimental materials.Firstly,coal gangue was activated by supercritical（subcritical）water added with inorganic base as the activator,and a series of analysis of the products was carried out to obtain the extraction rates of SiO₂ and Al₂O₃.The experimental scheme,analysis method and calculation method were preliminarily estalishedSecondly,the influence of alkali on the supercritical hydrothermal activation of coal gangue was briefly analyzed.Through the analysis of XRD,ICP-OES and other characterization methods,it was found that the main product in activated samples were cancrinit,sodalite and kaolinite corresponding with NaOH activator,Na2CO3 activator and KOH activator.And these aluminosilicates were easy to soluble in hydrochloric acid.All the activated samples were treated with HCl to obtain SiO₂ and Al₂O₃.When 2.0 mol/L NaOH acted as activator,the dissolution rate of SiO₂ and Al₂O₃ were 70.41% and 65.74%,respectively.When 2.0 mol/L Na2CO3 was acted as activator,the dissolution rate of SiO₂ and Al₂O₃ were 77.03% and 71.57%,respectively.When 2.0 mol/L KOH was acted as activator,the dissolution rate of SiO₂ and Al₂O₃ were 71.46% and 83.04%,respectively.Thirdly,in order to broaden the temperature range,the subcritical hydrothermal activation experiments of coal gangue were carried out.At the same time,the methods to enhance the yields of silica and alumina separated from coal gangue by subcritical hydrothermal activation were also explored.It is found that the dissolution rate of silicon oxide was over 50% and the dissolution rate of alumina was above 80%,based on the results of XRD,ICP-OES,TG-DTG,FTIR and BET.The specific surface area of SiO₂ by separation and purification could reach 818.1 m2/g,and the purity could reach 96.3% and the purity of Al₂O₃ could reach 99.17%.Finally,the material balance,economic benefit analysis and environmental evaluation of the technology of supercritical（subcritical）water hydrothermal activation of coal gangue combined with acid leaching to extract silicon and aluminum,were calculated and analyzed primitively.It is proved that the new technology is an excellent process with high added value,high resource utilization and environment friendly.