Durability and leaching behavior of mine tailings-based geopolymer bricks

Disposal of mine tailings (MT) in impoundments may have adverse environmental impacts such as air pollution from dust emissions and release of heavy metals to surface and underground water. Geopolymerization as an environmentally-friendly and sustainable method has been used to stabilize MT so that they can be used as construction material. In this paper, the durability and leaching behavior of MT-based geopolymer bricks are studied by measuring unconfined compression strength (UCS), water absorption, weight loss, and concentration of heavy metals after immersion in pH = 4 and 7 solutions for different periods of time. Microscopic/spectroscopic techniques, SEM, XRD and FTIR, are also employed to investigate the change in microstructure and phase composition of MT-based geopolymer bricks after immersion in the solutions. To describe the leaching behavior of MT-based geopolymer bricks, the first order reaction/diffusion model (FRDM) is used to analyze the leaching test data. The results indicate that although there is a substantial strength loss after immersion in pH = 4 and 7 solutions, the water absorption and weight loss are small. The strength loss is mainly due to the dissolution of geopolymer gels as indicated by the microscopic/spectroscopic analysis results. The leaching analyses show that the heavy metals are effectively immobilized in the MT-based geopolymer bricks, which is attributed to the incorporation of heavy metals in the geopolymer network. The FRDM can satisfactorily describe the leaching behavior of heavy metals in the MT-based geopolymer bricks and the analysis results indicate that the solubility or reaction rate is an important factor controlling the leaching behavior.