Towards a Sustainable Mining: Reuse of Slate Stone Cutting Sludges for New Geopolymer Binders

In recent years, the mining industry of slate stone in Spain, from Castille and Leon, has grown significantly due to construction and building sector demands. The continuous accumulation of cutting sludges in ponds from mining and processing operations brings associated environmental problems if the cutting sludges are not properly treated. A potential environmental mitigation measure is the valorization of cutting sludges for the development of new binder materials through geopolymerization. Therefore, this research focused its attention on studying the feasibility of slate stone cutting sludges as a source of aluminosilicates for geopolymer conformation. For this experiment, the mining raw material was analyzed through a typical characterization test campaign in order to validate its feasibility as a source of aluminosilicates for geopolymerization. Subsequently, geopolymers were prepared with slate stone cutting sludges and a 12 M concentration using different Na 2 SiO 3 /NaOH ratios (5, 2.5, 1.6, 1.25, and 1). Geopolymer samples were tested, and their physical and mechanical characteristics were evaluated. The test results show that an alkali activator with a 2.5 ratio led to better mechanical and physical properties, with a 7-day compressive strength value of 27.23 MPa. Therefore, this research aims to demonstrate that slate stone cutting sludge could constitute a sustainable binder material for construction purposes.