Recovery of Thickened Kaolinite Suspension Properties Through Shear

• Author / Creator

  Sun, Yijia

• The production of a tailings waste stream is ubiquitous to mining and mineral processing operations, especially in Alberta’s oil sands industry. Due to the presence of colloidal clays such as kaolinite, which do not naturally sediment in suspension, water recycling and land reclamation remain both a priority and a challenge. To facilitate the separation of fine solids by gravity, tailings are commonly treated with additives to promote the formation of large, fast-settling aggregates. Unfortunately, shearing forces inherent to pipeline transport are known to fracture these aggregates, ultimately
  reducing the effectiveness of any tailings thickening efforts. However, under certain conditions, aggregates have been observed to re-form after rupture, though the circumstances under which this happens are not well understood. Therefore, the foremost objectives of this study are to determine
  the suspension conditions which have the greatest impact on the potential for fragmented kaolinite aggregates to re-form, and to establish a connection between suspension rheology and the shear energy required to induce re-aggregation.

  A number of re-aggregation experiments were performed to determine the extent of shear-induced re-configuration possible. Kaolinite clay suspensions of varying solids concentration (28 wt% to 42 wt%), thickening additive dosage, and suspension pH (4.3 to 9.8) were sheared
  using precisely defined protocols in a concentric cylinder rheometer. As fractured aggregate fragments collide, a combination of hydrodynamic and surface forces produce an equilibrium particle agglomerate size. Since the rheological properties of a suspension are strongly dependent
  on the apparent volume fraction of flocs, monitoring the torque response to constant shear provides insight into the evolution of clay aggregate size. The results established that suspensions with the highest clay solids fraction were the most amenable to re-aggregation, while polymer-dosed suspensions showed the least potential for structural recovery, even at relatively high solids concentration of 40 wt%. Furthermore, it was concluded that the energy input required to induce structural changes in kaolinite aggregates can be inferred from a measurement of the initial suspension rheological properties through a reference point defined as the hysteresis loop
  closure. Despite differences in initial composition and conditions, this reference point consistently identified the shear energy necessary to produce the greatest rheological increase in any shear history-dependent kaolinite suspension.
  This study establishes a connection between suspension rheology and re-aggregation. It has been shown that previously degraded rheological properties in kaolinite suspensions can be restored by applying the appropriate level of shear in a concentric cylinder rheometer. From these
  results, it can be inferred that the undesirable rupture of thickened tailings aggregates in pipe flow is possible to reverse under certain conditions. Most importantly, the energy required to produce aggregate restructuring can be determined from a relatively simple bench scale test, and warrants further investigation.

• Subjects / Keywords

  • Kaolinite
  • Reaggregation
  • Rheometer
  • Shear
  • non-Newtonian
  • Tailings
  • Aggregation
  • Rheology
  • Rheopexy
  • Thixotropy

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3H708G7W

• License

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