Innovative green binders: Harnessing mine tailings and by-products for sustainable construction

With increasing environmental concerns and the need for sustainable construction materials, alkali-activated binders offer a promising alternative to traditional Portland cement. Mine tailings (MT), a significant by-product of mining operations, pose substantial environmental challenges due to their potential for soil and water contamination. This study investigates the characteristics of alkali-activated binders derived from MT, supplemented with granulated blast furnace slag (GBFS) and alum sludge (AS). Additionally, it examines the impact of substituting commercial sodium silicate (Na 2 SiO 3 ) with sodium silicates sourced from rice husk ash (RHA) in these binders. The binders achieved 21-day compressive strengths ranging from 15 to 37 MPa, demonstrating their potential as alternative construction materials. The inclusion of AS significantly reduced the flow properties of the binders without substantially enhancing their mechanical properties. Replacing commercial Na 2 SiO 3 with RHA led to a reduction in strength; however, binders with 0% commercial Na 2 SiO 3 still achieved a 21-day compressive strength of 15 MPa. Microstructural analysis revealed that the primary reaction product in all binders was a C-(N)-A-S-H-type gel. Reducing the content of commercial sodium silicate increased the presence of partially or unreacted MT particles and micropore volume, indicating incomplete geopolymerization. The total porosity ranged from 1.4% to 7.9% for the samples. Leaching tests showed a decrease in zinc (Zn) leaching in the geopolymers compared to the raw materials, while iron (Fe) leaching remained within Australian drinking water aesthetic standards. However, an increase in arsenic (As) leaching was observed, underscoring the need for further research on its mobility within the geopolymer system. This study highlights the potential of using industrial by-products, such as mine tailings, in the development of sustainable construction materials while also identifying key challenges for practical application. By repurposing MT, we can mitigate its environmental impact and contribute to more sustainable construction practices. • We observe a 40% reduction in 21 day strength of water cured samples compared to heat-cured samples. • We find that adding alum sludge reduces flow without significantly improving strength. • Reducing commercial Na 2 SiO 3 content decreased the flow of fresh binder. • Replacing commercial Na 2 SiO 3 with RHA/NaOH gave a 21-day strength of 15 MPa. • We note an increase in total porosity and maximum pore diameter with reduced commercial Na 2 SiO 3 .