Effect of Laminar Shear on the Aggregate Structure of Flocculant-dosed Kaolinite Slurries

  • Author / Creator
    Vaezi Ghobaeiyeh, Farid
  • The research was conducted to investigate effect of hydrodynamic conditioning on the flocculation of the oil sands fine tailings. The main focus was the effect of shearing on the structure of flocculated aggregates and the extent of reflocculation occurring upon cessation of shearing. An experimental technique was developed based on laminar tube flow. This allowed a more realistic estimation of the shear rate to which an aggregate was exposed, and direct sampling of the aggregate to minimize alteration of the aggregate structure by sampling. A combination of aggregate settling velocity and image analysis was used to determine the aggregate structural parameters, i.e. size, shape, density and fractal dimension.

    The laminar flow device was used to investigate the flocculation kinetics and evolution of the aggregate structure. Aggregates were formed by flocculation of kaolinite particles, as model clay, with an anionic flocculant under physicochemical conditions similar to those of oil sands tailings. Detailed statistical analysis showed that a dynamic equilibrium flocculation state was established and the formed aggregate structure was statistically reproducible.

    The accuracy of aggregate density and fractal dimension measurements using size and settling velocity data was improved by developing a new non-spherical drag coefficient correlation. The new correlation uses only two dimensional geometrical parameters obtained from image analysis. The correlation is applicable to the study of fluid particle dynamics for any fragile and non-spherical particles, including the type produced during the treatment and dewatering of oil sands tailings.

    The flocculated aggregates, with well-defined and reproducible structures, were exposed to a wide range of shear rates for different periods of time. The shearing experiments were performed using the laminar tube flow device. The results showed that shearing reduced aggregate size, increased aggregate density and compacted the structure. Also, shearing ultimately produced aggregates having more spherical shapes. Both the magnitude and duration of shearing were found to be important. The degraded aggregates could reflocculate to some degree upon cessation of shearing. The extent of reflocculation was almost independent of the shearing history and the reflocculated aggregates regained much of their original structural properties (i.e. before shearing) with a slight structural compaction.

    The results suggest that the controlled shearing and subsequent reflocculation can improve de-watering and consolidation properties of flocculated fine tailings.

  • Subjects / Keywords
  • Graduation date
    Spring 2013
  • 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.