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

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. (C) 2016 Elsevier Ltd. All rights reserved.