Extraction And High Value Utilization Of Si And Al Elements From Coal Gangue

The characteristics of my country’s energy structure of"rich coal,lean oil,and little gas"determine that coal occupies a dominant position in energy utilization,and will not change for a long time in the future.Nevertheless,a large amount of coal gangue has been produced with the mining of coal.The existence of coal gangue will have many adverse effects on the environment.However,from the current situation of comprehensive utilization of coal gangue,the main problem at present is the lack of utilization methods that combine high utilization rate and high value-added of coal gangue.In this work,the effective elements of coal gangue were extracted by alkali fusion activation and acid leaching from the above-mentioned coal gangue,and converted into a variety of high value-added aerogel materials using different preparation processes.At the same time,a variety of characterization and detection methods were used to conduct in-depth research on the samples.The specific research contents are as follows:（1）The technological process of extracting silicon and aluminum elements from coal gangue is proposed through experimental research,and the optimum parameter including ratio,reaction temperature and reaction time between coal gangue and Na2CO3 are determined.By the way,coal gangue can be effectively activated,and the obtained clinker reached the maximum decomposition rate in acid solution,which paved the way for the efficient leaching of silicon and aluminum elements in the form of solution in the later stage.（2）Using calcined gangue clinker,pure SiO₂ aerogel powder and SiO₂-Al2O3 binary composite aerogel powder were prepared by sol-gel process and supercritical drying method.The effect of different p H values on the gel during the clinker decomposition process,the effect of the volume of water added to the clinker on the gel,and the effect of the p H value of the aluminum-rich silica gel on the properties of the aerogel samples were studied.（3）SiO₂-Al₂O₃/agarose composite aerogel beads（SCABs）with certain toughness and ultra-high specific surface area were prepared by soaking method.The effects of different concentrations of SiO₂ sol containing Al³⁺and agarose solutions of different concentrations on the prepared SCABs were investigated.The characterization and analysis were carried out by scanning electron microscope,infrared spectroscopy,thermogravimetry,thermal insulation and so on.The proposed method for preparing SCABs has simple preparation process and low preparation cost,and is suitable for large-scale industrial production.（4）It is proposed to prepare the pomegranate-like structure composite aerogel beads（CABs）by the secondary gel method,and the feasibility of the method is verified by experiments.The CABs were prepared by combining the hydrophobic SiO₂-Al2O3 aerogel powder prepared based on coal gangue with polyvinyl alcohol and agarose with hydrophilic groups by a secondary gel method.The special wettability（hydrophilic on the outside and hydrophobic on the inside）not only preserved the three-dimensional nanoporous structure of the aerogel,but also solved the problem that it is difficult to use in combination between hydrophobic aerogel powder and the water-rich cementitious matrix due to its low bonding strength.In addition,the special structure also brings the excellent mechanical properties of this composite material,which expands the application field of aerogels.