Compression Behaviours of Mine Tailings Materials under Microbially Induced Calcite Precipitation (MICP) Treatment
Creators: Atashgahi, Shima
Publisher: name: University of Alberta Library
Year: 2024

<p>Tailings materials generated as a by-product of bitumen extraction in Canada’s oil sands industry present significant challenges due to their low consolidation rate, high water content, and potential environmental impact. Therefore, finding a sustainable practice for improving the engineering properties of mine tailings is of paramount importance. This study aims to explore the use of Microbially Induced Calcium Carbonate Precipitation (MICP) treatment in stabilizing tailings materials. Previous investigations have shown promising results in soil stabilization using MICP (DeJong et al. 2010). However, limited information is available regarding the application of MICP on mine tailings. Improving the compression behavior of sandy tailings materials, which can be used as construction materials, is important to help prevent dam failures caused by slope instability, foundation failure, and static liquefaction (Kossoff et al. 2014). Additionally, improving the physical stability of post-spill tailings is considered instrumental in minimizing the risk of further material dispersion and reducing the risk of contamination to nearby resources (Kossoff et al. 2014). Another important aspect related to mine tailings is the acceleration of the consolidation rate of tailings slurry, which results in a reduced need for long-term storage and enables more efficient progressive reclamation (Kabwe et al. 2024).<br>
Based on the identified needs for improving tailings materials, this study employed the MICP treatment method to enhance the compression resistance and hydraulic conductivity of tailings materials. Research involved conducting a series of 1-D compression tests on sandy tailings (96.3% solid content and 2.96% fines content) and fine tailings (25% solid content and 99% fines content), considering factors, i.e., different cementation and water content levels to compare the engineering properties of the studied materials before and after MICP treatment. Additionally, the compressibility and hydraulic conductivity of transition tailings (56% solid content and 45% fines content) were analyzed using large strain consolidation tests.<br>
The findings from sandy tailings revealed that the untreated sample exhibited rapid displacement from initial loading, with yield stress at 640 kPa and 4.48% axial strain. In contrast, the yield stresses for the MICP-treated samples, which varied in cementation contents, were significantly higher at 2560 kPa, with lower axial strains ranging from 2.2% to 1.7%. Additionally, results from 1-D compression tests on treated fine tailings with water contents ranging from 30% to 50% demonstrated that an increase in water content led to a greater reduction in void ratio, at a maximum load of 500 kPa (0.019-0.35), while the untreated samples showed higher values (0.30-0.51). These results indicate that as the extent of cementation increases and water content decreases, the treated materials become less compressible and more resistant to deformation. Finally, results from large strain consolidation tests demonstrated that as effective stresses increased to 100 kPa, higher axial strains and compression were observed in the MICP-treated sample (120.2%) compared to the untreated sample (43.2%). Also, treated sample consistently exhibited higher hydraulic conductivity (2.75 x 10-8 to 9.32 x 10-10) compared to the untreated one (2.64 x 10-8 to 7.93 x 10-11). The results demonstrated that calcite (CaCO3) acts as a natural cement, binding particles together into larger aggregates, allowing water to escape more easily and thus accelerating the consolidation process after the applied load.</p>