Flocculation-assisted dewatering of fluid fine tailings using a volute screw press

  • Author / Creator
    Wang, Chen
  • Rapid, efficient and economical water removal from fluid fine tailings represents a major challenge to many industries, including mineral processing, food processing, waste water treatment and oil sands extraction. In the absence of large-scale fine tailings processing facilities, there will be an escalating accumulation of such waste material in containment areas, which requires careful, extensive and often costly measures for hazards mitigation. A flocculation-assisted two-stage process to continuously dewater oil sands fluid fine tailings using a volute screw press is developed. A cationic-anionic flocculant scheme was applied first to the fluid fine tailings, which flocculated essentially all suspended solids in the slurry. The concept of elastic and plastic deformations for metallic solids was extended and successfully applied to describe compression and subsequent water release characteristics of semi-solid tailings sediment. The newly developed “controlled vertical strain test” (CVST) enables bench-scale measurement on the theorized impact of flocculants on sediment compressive dewaterability. A new empirical parameter named “compressive dewatering index” (CDI) was obtained from the sediment compression response curve via the CVST method. The flocculated slurry was introduced to the volute screw press through a series of inclined steel rings (volute plates), and carried upwards by a central auger screw. Unobstructed and self-cleaning spacing between all volute plates ensures removal of unhindered supernatant, while large flocs of sufficient mechanical strength were retained and compressed by the screw. Field test work at Canadian Natural Resources Limited with a prototype volute screw press demonstrated successful production of stackable cake containing 55 - 60 wt% solids at 5 - 7 kg dry solids/h production rate. The field test results showed a strong linear correlation between the CDI and the filter cake dry solids content produced by the volute screw press. Such correlation allows predictive evaluations on the volute screw press dewatering performance at bench-scale. For elastic sediments, the slope of this linear correlation is termed as the CDI gain of the fluid fine slurry. This intrinsic and material-specific parameter could be used to universally classify any given fine fluid mineral slurry in its dewatering difficulty by mechanical means. The findings from this study could serve as a unified theoretical framework for future research on post-flocculation dewatering of fluid fine tailings by external mechanical forces as encountered in centrifuge and filtration.

  • Subjects / Keywords
  • Graduation date
    Fall 2017
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • 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.