Sodium-based alkali-activated foams from self-ignition coal gangue by facile microwave foaming route

To solve the problems of difficulties in reuse and low utilization of coal gangue, a high value-added strategy was proposed using coal gangue to produce porous ceramic materials. Alkali-activated coal gangue foams were fabricated using self-ignition coal gangue without additional minerals by a facile microwave foaming route. After simply mixing alkaline agents with the waste material, foams can be rapidly obtained under microwave heating treatment within 15min. The effect of alkaline concentration, curing condition, and high-temperature treatment on the total porosity, density, porous morphology, structural characteristics as well as mechanical and thermal conductivity properties of the alkali-activated coal gangue foams was investigated. Results indicated that the properties of coal gangue-based alkali-activated foams were significantly affected by the alkaline concentration, curing condition, and heating treatment. The foams with 100% coal gangue as the mineral constituent can be used for cleaner productions such as sustainable construction insulation material and low-cost refractory material.