Abstract
Coal gangue, one of the main hazardous emissions of purifying coal from coalmine industry, is rich in silica and alumina. However, the recycling of the waste is normally restricted by less efficient techniques and low attractive output; the utilization of such waste is still staying lower than 15%. In this work, the silica aerogel materials were synthesized by using a precursor extracted from recycled silicon-rich coal gangue, followed by a single-step surface silylation and ambient pressure drying. A low density (~0.19 g/cm3) nanostructured aerogel with a 3D open porous microstructure and high surface area (~690 m2/g) was synthesized, which presents a superior thermal insulation performance (~26.5 mW·m−1·K−1of a plane packed of 4-5 mm granules which was confirmed by transient hot-wire method). This study offers a new facile route to the synthesis of insulating aerogel material by recycling solid waste coal gangue and presents a potential cost reduction of industrial production of silica aerogels.
Highlights
Silica aerogel is one of the hot topics nowadays, because of its exceptional physical properties, for example, high porosity and specific surface area, low density, and thermal conductivity [1,2,3,4,5,6]
After heat treating and HCl leaching, most of the quartz phase remained, the peaks assigned to kaolinite were no longer distinguished anymore, as shown in Figure 2, which correlates with a degradation of Al/Si compounds, the peaks belonging to iron mineral of siderite were getting weaker, especially at 750∘C and 850∘C treatments, which indicates an effective removal of Fe and Al compounds from the coal gangue, and most of the silicon phases were still retained
The pore size and surface area of the coal gangue derived aerogel are comparable to the typical aerogels prepared from tetraethyl orthosilicate (TEOS) and waterglass [28]; in this case, it could be assumed that the large macropores are the minority species and indicate that the aerogel materials prepared from coal gangue present similar structures as typical silica aerogel [29] and should display identical performance, that is, thermal insulation, to such material
Summary
Silica aerogel is one of the hot topics nowadays, because of its exceptional physical properties, for example, high porosity and specific surface area, low density, and thermal conductivity [1,2,3,4,5,6]. There are few reports on silica xerogel preparation from coal gangue, the reported utilization of the silicon resource was lower than 70%, and no systematical characterizations of such materials, but quite a lot of publications, were reported for precipitated silica fabrications [20,21,22]; the main challenge of aerogel preparation is controlling high SiO2/Na2O molar ratio in the extracted silicon sol (over 1 : 1, which needs to restrict Na+ loading or increase silicon concentration) [23] and high extraction efficiency of silica (which requires high Na+ concentration and large amount of solvent) and low concentration of impurities, such as Al, Fe, and Mg, in the final gels (which affects the transparence and thermal performance of aerogels). The study offers a feasible route for synthesizing silica aerogel from recycled waste coal gangue and presents potential niche markets established from such novel route synthesized aerogels
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