Towards coal mining waste valorization: Gangue as resource for the production of geopolymer and related alkali-activated materials

The high rate of coal production leads to the formation of huge amounts of waste and byproducts, including coal gangue (CG), which has become the largest industrial residue in the energy industry. Among new management strategies, recycling and valorization of CG to produce alkali-activated binder systems promises environmental and economic benefits, including carbon emission reduction, stabilization of contaminated or inert coal mining waste, and reduced consumption of primary resources used in the construction sector. This paper provides a critical and comprehensive review of earlier studies on using coal gangue as a resource for geopolymers and related alkali-activated materials (AAMs). More specifically, this review summarizes the physicochemical features of CG and discusses the main factors influencing the performance of AAMs based on them. The possible engineering uses of these materials are also covered. Additionally, it is important to note the limitations of coal gangue to make AAMs and identify where further research is needed.