| The massive accumulation of coal gangue without reasonable disposal can cause water and soil pollution as well as soil erosion and other environment problems. The atmospheric pollutants emitted from spontaneous combustion could also cause environment impacts. It is imperative to develop high value-added products involving high-tech comprehensive utilization technique, improve coal gangue utilization efficiency and expand the useful range of it. Coal gangue is pickled to remove impurities for obtain high value-added mesoporous material in the dissertation. This will not only alleviate the environmental pollution created by coal gangue accumulation in Huainan and Huaibei mining area, Anhui Province, but also keep its economy and other social aspects developing lasting, fast and healthy. Meanwhile, solid waste disposal is a great deal of environment, economical and societal benefits.In the dissertation, coal gangue is acquired from Huainan and Huaibei mining area, the effect of microwave activation and thermal activation is discussed in detail. Coal gangue is activated by calcination and pickled to remove impurities. Effect of pickling process on specific surface area has been investigated. Pore volume and specific surface area are both improved by optimizing process parameter; mechanism of action during pickling is also discussed.The major chemical compositions found in the samples are SiO2, Al2O3, CaO and Fe2O3. The largest component in the coal gangue is SiO2,43.95%, followed by Al2O3 (14.293%), CaO (8.82%) and Fe2O3 (5.55%). The mineral phased found in the coal gangue samples are kaolinite, quartz, calcite and siderite. The research of microwave activation indicates that, free water and absorbed water can be removed under microwave irradiation of 0.715-1.100 kW power for 2-12 min, calcite phase is also decomposed. However, layer structural water in kaolinite fail to dehydration, kaolinite and siderite cannot be decomposed, which lead to the failure in excitation of coal gangue. The research of thermal activation indicates that, kaolinite, calcite and siderite in coal gangue can be decomposed by calcination, generating amorphous noncrystalline products. Calcite and siderite can be decomposed at 500?, kaolinite start to lose layer structural water at 500? and decompose completely at 850?. Holding time has no evident effect on decomposition of kaolinite. The optimum process parameters:calcinating at 850? for 2 h and cooling to room temperature.The mesoporous material derived from coal gangue has been prepared. The results indicate that pickling temperature, duration and acid dosage have significant effects on specific surface area of mesoporous material. In this paper,2 g raw material is calcined at 850? for 2h to generate thermal activated coal gangue,16 mL mixed acid is added, pickling at 80? for 4 h. It is found that the maximum specific surface area reaches at 207.57 m2/g, mean pore size is 6.34 nm, and total pore volume is 0.33 cm3/g. Calcination activation has great impact on the result of pickling, the specific surface area of the coal gangue sample without calcination activation and microwave irradiation is much less than that of coal gangue with calcination activation. The acid merely can corrode amorphous noncrystalline active material during pickling treatment. When the samples are grinded for the second time, specific surface area can be significantly improved. The specific surface area of the sample with grinding for the second time is up to 299.25 m/g, mean pore size is 5.37 nm, total pore volume is 0.40 cm3/g. Grinding for the second time is an effective way to expose active substance. Due to the sudden cooling from high temperature, stable inactive crystal phase transform into amorphous noncrystalline matter, which results in the activity of coal gangue. Hence the activating treatment of coal gangue is the precondition of preparing mesoporous material. |
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