Durability of red mud-fly ash based geopolymer and leaching behavior of heavy metals in sulfuric acid solutions and deionized water

• RFFG showed comparable resistance against low pH sulfuric acid to OPC.
• Depolymerization and dealumination were the main reasons for RFFG’s mechanical deterioration.
• The concentrations of leached heavy metals in RFFG were lower than respective EPA limits.

The durability and heavy metal leaching behavior of red mud-class F fly ash based geopolymers (RFFG) were investigated in this study. RFFG specimens were soaked in sulfuric acid solutions (pH = 3.0) and deionized water (pH = 7.0) for 1–120 days, and then their remaining mechanical properties and the change in the microstructures were characterized with unconfined compression tests, three-point bending tests, scanning electron microscopy, X-ray diffractometer and Fourier transform infrared spectroscopy, respectively. The leaching behavior of heavy metals in RFFG samples after soaking up to 14 days was also examined with atomic absorption spectroscopy. The RFFG samples’ resistance against sulfuric acid was comparable to the ordinary Portland cement (OPC), and their mechanical degradation was mainly attributed to the depolymerization and dealumination of geopolymer gels. The highest concentrations of the heavy metals leached by the sulfuric acid from the RFFG samples were much lower than the respective US EPA limits for soil contamination.

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