Accelerating Polymer Degradation to Explore Potential Long Term Geotechnical Behaviour of Oil Sands Fine Tailings

• Author / Creator

  Stienwand, Kelsey Alissa

• Many tailings’ technologies used in the Athabasca oil sands require the use of chemical amendments such as synthetic flocculants to densify tailings by releasing water. It is anticipated that the synthetic flocculants will eventually degrade with time leaving only a mineral soil structure behind. The geotechnical properties following potential degradation of the amendments are unknown. This research provided the opportunity to further understand the long-term strength behavior of polymer amended tailings deposits. Specific objectives included: evaluation of potential polymer degradation methods to accelerate degradation of chemical amendments, compare impact of thermal polymer degradation on geotechnical behaviour on control samples, compare impact of polymer degradation on geotechnical behaviour on various chemically amended samples and finally to compare impact of polymer degradation on the geotechnical behaviour of various percent solids/ void ratios to reflect an in-situ tailings deposit.
  
  Two degradation pathways were investigated: chemical/thermal degradation and biological degradation. The clay slurries and tailings samples used in the research were kaolinite, fluid fine tailings, flocculated fluid fine tailings, and centrifuge cake. Various techniques were employed to compare the impact of degradation, which included oscillatory rheometry, vane shear, and SEM imaging. Kaolinite and fluid fine tailings were used as control samples to determine if the thermal degradation pathway was altering the mineral structure of the polymer amended samples. Additionally, large strain consolidation (LSC) was utilized to consolidate centrifuge cake samples to simulate various void ratios that occur in in-situ tailings deposits.
  
  In the control samples for the thermal degradation, the results showed changes to the rheological measurements and no changes to structure in the SEM images. Changes occurred from the heat treatment process; however, it is difficult to determine whether it was a result of the change in percent solids that occurred during the heat treatment process or if the process was altering the mineral structure of the clay / tailings sample. The second polymer degradation method used was bacterial degradation. This pathway was explored using a commercially available bacterium. It is sold under the name ‘Frac-Bac’ and was provided for this research by Re-Nuu Production Optimization Inc. The results suggest impacts to the long-term strength behaviour of polymer amended tailings, however, many of these changes to the measured parameters were low to moderate in magnitude (average 20% decrease). When comparing the two polymer degradation methodologies, less error was introduced in the bacteria treated samples and consistent negative impacts were seen in all parameters.
  
  The results suggest negative impacts to the long-term strength behaviour of polymer amended tailings; however, many of these changes were low to moderate in magnitude (average 30% change). Errors introduced from the limitations of the heat treatment process (change in percent solids) are known to have large effects on the measured shear strength in oil sands tailings and were difficult to control in the experiment. It appears that a change in structure occurred from the heat treatment process, however it is difficult to quantify whether it was a result of the change to percent solids or from degradation of the polymer itself. The results from the bacteria treated samples showed consistent negative impacts seen in all parameters.
  
  Some suggestions for improving future work are additional research on the bacterial treatment process as the pathway showed consistent negative impacts to the samples and introduced fewer errors, quantifying error in the oscillatory rheology for each tailing sample, and improvements to the heat treatment process to ensure that moisture content / percent solids of the samples stay within defined parameters.
  This research provided the opportunity to further understand the long-term strength behavior of polymer amended tailings deposits which found degradation of flocculants could have some negative impacts.

• Subjects / Keywords

  • polymer degradation
  • oil sands fine tailings

• Graduation date

  Fall 2021

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/r3-22gg-w411

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.