The effects of lithium slag on microstructure and mechanical performance of metakaolin-based geopolymers designed by response surface method (RSM)

Abstract This study reports the effects of lithium aluminosilicate residue (LARS) powder, a byproduct in the process of extracting lithium from lithium pyroxene, on microstructure and mechanical performance of metakaolin (MK)-based geopolymer, and RSM was used to obtain the optimal mixing proportions. The compressive strength of all groups of samples was tested to characterize the mechanical properties of the LARS-MK geopolymer, whereas Scanning Electron Microscopy-Energy Dispersive Spectrometer (SEM-EDS) and BET were employed to characterize the microstructures and pore structure. To identify the products formed in the geopolymerization process, the phase compositions and molecular bonds were analyzed using X-ray diffraction (XRD) and Fourier infrared spectrometer (FT-IR). The results show that the introduction of LARS degrades the microstructure of geopolymer in the early ages. However, it is beneficial for the strength development after 28 days of curing when a proper amount of LARS powder was introduced, and the optimal compressive strength of the samples cured for 28 days with about 10% LARS and 105% activator is 77.5 MPa. Meanwhile, the deteriorated mechanical performance at the age of 180 days indicates that the addition of LARS powders may not favor the late age performance of samples. Furthermore, the microstructural analysis indicates that the introduction of LARS may lead to new phases such as rankinite or albite. The findings suggest that LARS has a great potential in developing geopolymers and provides a unique solution to its waste management.