From Waste to Thermal Barrier: Green Carbonation Synthesis of a Silica Aerogel from Coal Gangue

A sustainable pathway for converting low-value solid waste (Coal gangue, CG) into high-performance thermal insulation materials through a green synthesis strategy has been demonstrated. The SiO2 was successfully and efficiently extracted from CG in the form of sodium silicate. The subsequent sol–gel process of sodium silicate solution utilized an innovative CO2 carbonation method, which replaced the conventional use of strong acids, thereby reducing the carbon footprint and enhancing process safety. Hydrophobic SiO2 aerogel was subsequently prepared via ambient pressure drying, exhibiting a high specific surface area of 750.4 m2/g, a narrow pore size distribution ranging from 2 to 15 nm and a low thermal conductivity of 0.022 W·m−1·K−1. Furthermore, the powdered aerogel was shaped into a monolithic form using a simple molding technique, which conferred appreciable compressibility and resilience, maintaining the low thermal conductivity and hydrophobicity of the original aerogels, ensuring its functional integrity for practical applications. Practical thermal management tests including low and high temperature, conclusively demonstrated the superior performance of the prepared aerogel material. This work presents a viable and efficient waste-to-resource pathway for producing high-performance thermal insulation materials.