| The exploitation and utilization of coal play a huge role in the social economy. Atthe same time, it also has significant negative impact on the environment. More thanone billion tons of coal gangue is regarded as a kind of the largest industrial solidwaste in China. Its resource-oriented utilization has become the focus of research. Inthis paper, coal gangue from Henan Dayugou Hongqi Coal Group was used as startingraw material. Analytical techniques such as inductively coupled plasma emissionspectrometer (ICP-AES), high-resolution field emission scanning microscope (HR-FESEM+EDS), X-ray diffraction (XRD), simultaneous thermal analyzer and particlesize analyzer were introduced to characterize the properties of coal gangue ore andprepared specimens so as to obtain a comprehensive evaluation of coal gangue.Coal gangue mineral was sorted, crushed, sieved and purified followed bysintering at high temperatures. Mullite homogenization material and porouslightweight mullite material were prepared. This work mainly discussed the influenceof technological parameters such as particle size, sintering temperature and soakingtime on the mullitization of coal gangue, and then applying to the industrial synthesisof mullite raw materials. The significant results were obtained as follows:1. The classification of coal gangue used in this experiment belongs to aluminumrich coal gangue. The main chemical compositions of coal gangue clinker are Al2O3(67.33%) and SiO2(22.05%). The main phases are diaspore (AlOOH) and a smallamount of kaolinite and pyrophyllite. Microscopic morphology presents as flake-likeunder the scanning electron microscopy.2. Sintering experimental research (1000~1500℃) of coal gangue raw ore showsthat a small amount of mullite micro-crystal is generated at1250℃and the mullitecontent increases with the increase of sintering temperature. Pyrolysis activation studyindicates that coal gangue powders have the best activity by sintering at600℃for0.5h. Diaspore loses hydroxyl water and generates amorphous Al2O3. The specificsurface area is big and coal gangue particles present in loose state under SEM.3. Briquetting firing mullite with bulk density of2.81g·cm-3and apparent porosityof6%can be obtained by sintering at1600℃for3h using coal gangue powders ball milled for3h (D50=6.4μm) as raw material. Main phases of the sintered samples aremullite solid solution (Al4.56Si1.44O9.72) and corundum (Al2O3), the relative content ofmullite is74%. Mullite crystals grow up in good condition and develop into columnarwhich are parallel to the C-axis with the cross-sectional shape of quadrangle and grainsize of5~14μm. Mullite crystals cross with each other and constitute an interlockingnetwork structure. Corundum crystals develop into columnar or drum shapes anddistribute around the mullite crystals.4. Porous mullite is prepared by using Dayugou coal gangue mineral as the rawmaterial, corn starch as pore-forming agent, and PVA solution as binder under thetemperature of1500℃for3h. The bulk density and apparent porosity are1.19g·cm-3and62%respectively. Sintered samples contain two phases of mullite solid solution(Al4.80Si1.20O9.60) and corundum (Al2O3). The relative content of mullite increases withthe increase of sintering temperature and reaches73%at1500℃. Mullite crystals growup in good condition and develop into columnar which are parallel to the C-axis withthe cross-sectional shape of quadrangle and grain size of3~10μm. Due to the particlesize of corn starch is small, the pores distribute uniform and are mainly microporeswith leptosomatic shape and the size is around1~5μm. |
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