Oil Sands Mature Fine Tailings Consolidation Through Microbial Induced Calcite Precipitation

  • Author(s) / Creator(s)
  • The accumulation of mature fine tailings (MFT) in tailings ponds has been a concern of the oil sands industry and regulators for decades. Previous studies and current practices for fine tailings consolidation focus on the addition of inorganic and organic additives to reduce MFT production and accumulation. These treatment processes are were not sufficiently efficient in reduction of fluid tailings accumulation. In addition, treatments using chemical and polymer additives do not effectively increase the solids content of the settled tailings to more than 50%, which is lower than the required level for the surface trafficability mandated in Directive 074 issued by the Energy Resources Conservation Board. The development of treatment technologies to remove the last remnants of water from the settled tailings is critical. It is desirable to develop more efficient and effective techniques for MFT consolidation to reduce the risk to wildlife and ecosystems in the surrounding area. In this study, the performance and mechanisms of a microbial induced calcite precipitation (MICP)-assisted MFT settling and consolidation method was assessed. MFT samples of 35 wt% and 60 wt% were treated with MICP. The volume of released water, the solids content of the tailings, and the shear strength of MFT were measured to evaluate the effects of MICP on MFT consolidation. MFT initial settling curves were developed by monitoring the change of the water-solid interface position over time. To investigate the surface interaction mechanisms involved in the process, the calcium concentration of MFT release water was measured and the size and shape of MFT particles were observed by scanning electron microscopy (SEM). The results showed that although treatment with ureolysis-driven MICP effectively accelerated diluted MFT settling, ureolysis-driven MICP had little capacity to settle solids in raw (undiluted) MFT samples using tested reagents concentrations. In terms of MFT consolidation, our results clearly showed that ureolysis-driven MICP can accelerate raw MFT consolidation, leaving compact sludge with significantly enhanced shear strength within 24 hours of the experiment. Consolidation of the settled solids and settling of the MFT slurry through ureolysis-driven MICP might be achieved through precipitation of calcite on bacteria and solid surfaces, altering surface characteristics of particulate materials, and reducing steric or electrostatic stabilizing effects among particles. The denitrification-driven MICP did not show promising results in terms of either MFT settling or consolidation. Denitrification may require more time and/or additional nutrient addition to accelerate the denitrification process, and to settle and consolidate MFT. Ureolysis-driven MICP provides several advantages compared to traditional chemical additives currently used or studied to accelerate MFT consolidation: (1) ureolysis-driven MICP is effective for consolidating MFT from different sources and with different surface properties; (2) although mixing is needed to introduce the bacterial culture to MFT, mixing conditions do not significant impact the effectiveness of MICP-assisted consolidation process; (3) the key sources (calcium and carbonate ions) required to expedite CaCO3 precipitation and MFT settlement are readily available in tailings; (4) the required dosage of urea is much less than that of other traditional chemical additives; and, (5) CaCO3 precipitation reduces the calcium concentration, potentially enhancing the quality of the recycled water. For future research, experimental conditions for ureolysis-driven MICP can be improved by optimizing stoichiometric amounts of Ca and urea, bacterial growth conditions and nutrient levels. Field application strategies for urea and bacterial culture should be evaluated. Options for anaerobic calcite precipitation should be tested, particularly processes that utilize endogenous microorganisms. The options of combining MICP to other consolidation processes and to further improve MFT consolidation and strength should be tested and evaluated. Long-term studies on the impact of MICP assisted MFT settling and consolidation on land reclamation should be performed.

  • Date created
  • Subjects / Keywords
  • Type of Item
  • DOI
  • License
    Attribution 3.0 International