Abstract
Coal gangue-based geopolymer (CGGP) is one of the hot spots existing in the recycling of coal gangue resources due to its good comprehensive mechanical properties. However, the coal gangue structure is stable and reactivity is poor, so the coal gangue needs to be activated before utilization. In this paper, the microstructure changes of activated coal gangue by different mechanical and thermal activation methods, as well as the mechanical properties and microstructure changes of the CGGP specimens were studied by experimental investigation. The results indicated that mechanical activation and thermal activation were two effective methods to change the reactivity of coal gangue, which consisted of destroying the stable kaolinite structure and improving the activity of coal gangue. Conversely, part of the amorphous structure in coal gangue was destroyed when the activation temperature reached 900 °C, which was not conducive to the further enhancement of coal gangue activity. For the CGGP prepared by thermally activated coal gangue and modified sodium silicate alkali solution, the uniaxial compressive strength of the CGGP specimens decreased with thermal activation temperatures of the raw coal gangue materials at 700 °C, 800 °C, and 900 °C. The main reason for this was the lower amount of the active metakaolin structure in coal gangue at 900 °C, which was not conducive to the geopolymerization process.
Highlights
China is one of the large energy producer and consumer countries in the world, mainly relying on coal
The intensity reduction of the kaolinite structure indicated that the stable crystal structure of kaolinite in coal gangue can be effectively destroyed by mechanical grinding
Mechanical activation and thermal activation are two effective methods for changing the reactivity of coal gangue, whereby both can destroy the stable kaolinite structure and improve the activity of coal gangue. Both FTIR and X-Ray Diffraction (XRD) spectra showed the removal of inner surface hydroxyl and inner hydroxyl, a decrease of Si–O–AlVI structure, and an increase of AlIV –O structure in the activated coal gangue
Summary
China is one of the large energy producer and consumer countries in the world, mainly relying on coal. Long-term and large-scale development of coal resources lead to massive accumulation of coal gangue [1,2]. In a coal mining environment, the large amount of coal gangue piled up on the ground encroaches the land, and pollutes both the air and water environments [3,4,5], seriously threatening the ecological security of the mining area and the sustainable development of the coal mining industry. Resource utilization of coal gangue is urgently required. Coal gangue are mainly reused as supplementary materials in backfilling technology, building construction, energy fuel, soil improvement, water purification, special cementitious materials, etc.
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