Immobilisation Efficiency and Mechanism of Pb2+ and Cr3+ in Red Mud-Based Geopolymer Grouts

In the present research, a geopolymer based on red mud was prepared for immobilisation of Pb 2+ and Cr 3+ , with the aim of improving the utilisation rate of red mud, which also represents an efficient and low-cost material for heavy metal solidification and grouting engineering. We investigate the mechanical strength and leaching characteristics of these geopolymer grouts, as well as immobilisation mechanisms through FT-IR, X-ray Diffraction (XRD), MAS-NMR, X-ray photoelectron spectroscopy (XPS) and SEM-EDS. Results showed that mechanical strength firstly increased and then decreased with the increment of the content in alkali activator molecule, that the aluminosilicate component in red mud can participate in the geopolymerisation reaction and that Pb 2+ and Cr 3+ could improve the mechanical strength of red mud-based geopolymer grouts when their content corresponds to 0.4 and 0.6 wt.%, respectively, and decrease it dramatically when the dosage is up to 1.0 wt.%. Chemical fractions of Pb 2+ and Cr 3+ revealed that the soluble and exchangeable fraction coud be converted to carbonate bound fraction, iron-manganese oxide and organic fraction, while the immobilisation rate was up to 91.46% and 95.86%. Characterisation results verified that adding Pb 2+ and Cr 3+ participated in the geopolymerizaiton process