Microstructure, strength development mechanism and CO2 emission assessments of molybdenum tailings collaborative fly ash geopolymers

A cost-effective approach is urgently needed to utilize molybdenum tailings (MoT), a mining byproduct with rising output. This study explored the preparation of molybdenum tailings collaborative fly ash (FA) geopolymers (MFG) from mechanically activated MoT and FA raw materials. Orthogonal experiments investigated the impacts of various parameters on the compressive strengths of the MFG. The macroscopic properties of MFG with different mixture ratios were evaluated. The microstructures and components of the MFG were characterized using various methods. Fractal dimensions (Ds) of pore structures in the MFG samples were determined. Carbon emissions resulting from the production of MFG geopolymers were calculated and evaluated using Low carbon Assessment. The findings showed that increasing the content of mechanically activated MoT in the MFG system decreased flowabilities and prolonged setting times. The optimal MoT-to-FA ratio for achieving the highest compressive strength of 31.26 MPa was 1:4, resulting in a Si/Al ratio of 2.03 in the MFG system. XRD, TG, SEM-EDS, and FTIR analyses confirmed the primary product of the MFG was a glassy hydrated sodium-aluminum silicate (N-A-S-H) gel. MIP analysis revealed that addition of mechanically activated MoT improved the pore structure of the MFG, leading to smaller pores. Additionally, for MFG composed solely of MoT or FA, the Ds was smaller, and smaller particles of the raw materials also led to smaller Ds values. Conversely, when the raw materials were mixed, larger Ds values were observed, and a closer volume fraction for the two raw materials resulted in larger Ds values. Furthermore, the carbon emission analysis revealed that the carbon emissions of MFG geopolymers were reduced by 45.4 %-64.3 % compared to traditional OPC slurries.