This presentation was presented at the 2018 COSIA Summit in Calgary, Alberta

ABSTRACT: The focus to date at oil sands operations has been on achieving stronger FFT by removing water and increasing the solids content. Oil sands operators currently treat FFT with polymeric flocculants, followed by initial dewatering, thickening, centrifugation or air-drying. These processes can result in significant increases in solids content. However, the further development of polymer-treated FFT into geotechnically viable material remains a challenge.

This study tested the following hypotheses:

  1. There are fundamental limitations to the ability of polymer-treated FFT to consolidate, to drain or transmit water, and to gain strength
  2. These limitations are due to colloidal and surface chemistry effects associated with FFT
  3. The addition of polymer as is currently practiced does not address surface chemistry effects and may even exacerbates the associated limitations
  4. The addition of both coagulant and polymer to FFT can produce materials with better geotechnical properties.

The first and fourth hypotheses were confirmed. The second and third hypotheses were found to be probable but were not confirmed. Findings show that the strength of FFT can also be enhanced by treatments that increase liquid limit and plasticity index, and that treatment of FFT with both coagulant and polymer has stronger effects on liquid limit and plasticity index than treatment with polymer alone. The result is that FFT treated with both coagulant and polymer starts to gain strength at a lower solids content than polymer-treated FFT, and continues to display higher strength as the solids content further increases. Improving FFT strength by treatment with both coagulant and polymer means that FFT can be ready for reclamation in times that are 10% to 30% less than those needed for FFT treated with polymer only.

This line of work seeks to improve the understanding of what can ultimately be expected of treated FFT in reclaimed mine landscapes and to provide insights leading to modified FFT management methods that will result in geotechnically viable materials. The use of other coagulants warrants further investigation. The magnesium sulphate coagulant chosen for this project was as mild as possible to avoid any confounding chemical reactions. Stronger coagulants, such as trivalent ions, acids, and polymeric coagulants, may have more significant effects on FFT strength gain.

Links: See profile on pages 118 to 120 of COSIA’s 2018 Tailings Research Report