Coal gangue, a solid waste generated during coal mining and washing, represents a silicon-rich feedstock that can be exploited for the economical synthesis of industrially valuable silica aerogels. An approach for the high value-added use of this waste material was demonstrated by researchers from China’s Changzhou University.

As a precursor for silica aerogels, sodium silicate was prepared from a cheap industrial waste coal gangue in a one-pot method for silica wet gel preparation. Mechanical stirring was applied to achieve solvent exchange/surface modification, followed by drying of gangue-derived wet gels at ambient pressure.

The resulting nanostructured aerogel had a high surface area of about 748 m²/g with a 3D open porous microstructure and a low density of approximately 0.18 g/cm³. The material displayed excellent thermal insulation performance with a thermal conductance value of 0.033 W/m/K. Reusing coal gangue boosted the synthetic yield of silica aerogel powder to 92%.

Scanning electron microscope image of silica aerogel powders at (a) 50 kX and (b) 100 kX magnification. Source: Jian Wei et al./Changzhou University

In addition to its use as a thermal insulating material, the coal gangue-based aerogel described in the journal Materials can also be applied as an absorbent of air and water pollutants.