Assessing the influence of metakaolin and slag on the geopolymerization of mine tailings as lightweight aggregates

Aluminosilicate-rich mine tailings (MTs) are promising materials for producing a novel type of lightweight aggregate (LWA) through geopolymerization. These tailings-based LWAs offer a potential replacement for both natural and industrial aggregates. Since many MTs lack sufficient reactive aluminosilicates for the geopolymerization process, adding amorphous materials such as slag and metakaolin can enhance geopolymerization, leading to the formation of higher-quality aggregates. This paper systematically investigates the effect of incorporating metakaolin on the physical, chemical, and mechanical properties of geopolymer-based LWAs, an area that has received limited attention in previous studies. Three mixtures were prepared to assess the supplement’s impact on the physical, chemical, mineralogical, and mechanical properties of LWAs: (1) 70% MTs and 30% slag, (2) 70% MTs and 30% metakaolin, and (3) 70% MTs, 15% metakaolin, and 15% slag. Incorporation of 30% slag resulted in LWAs with the highest strength, density, and lowest porosity, while 30% metakaolin reduced both density and strength. The optimal mix was achieved with 15% metakaolin and 15% slag. While slag contributed to strength improvement through the formation of calcium-silicate-hydrate (C-S-H) gel, metakaolin helped reduce bulk density by increasing the porosity and size of LWAs. Shortening the LWAs curing time to 5 days represented a significant improvement and enhanced the life-cycle performance of the metakaolin- and slag-modified aggregates compared with both previous tailings-based geopolymer LWAs and conventional industrial LWAs. Additionally, a life cycle assessment (LCA) of tailings-based aggregates revealed that LWAs including 15% slag and 15% metakaolin exhibited lower CO 2 footprint compared to industrial LWAs. • Lightweight aggregates were sustainably produced from mine tailings without sintering. • Slag and metakaolin significantly improved the strength and density of tailings-based aggregates. • Geopolymer aggregates showed a lower CO 2 footprint than industrial lightweight aggregates.