Yield stress augmentation of fine-particle slurries by coarse particles

  • Author / Creator
    Olayode, Abiodun E.
  • The transport of thickened tailings through pipelines in the mineral processing industry is challenging partly because knowledge of the yield stress of these complex non-Newtonian mixtures is required for design and optimal operation. Unfortunately, the yield stress of these mixtures cannot be accurately predicted partially because of the complexities introduced by the presence of coarse particles. It is known that the presence of coarse particles increases the yield stress of an initial flocculated fine-particle suspension. Also, the rheological characterization of these fine-coarse particle suspensions, which are often referred to as bimodal suspensions, is tedious and very difficult due to the fast settling nature of the coarse particles.
    In this study, an experimental program was completed to obtain improved vane yield stress data for a wide range of bimodal suspension types and concentrations. Kaolin slurries and industrial mature fine tailings were prepared at different concentrations and tested with three types of sand of different shapes and sizes. The performance of three semi-empirical yield stress correlations were tested and compared on these yield stress measurements. The contribution of coarse particle properties, such as shape and size, to yield stress augmentation was also investigated.
    Results show that in addition to concentration, the effect of coarse particle shape and size is significant and contribute to the yield stress increase. Specifically, higher yield stress values were observed with the angular sand when compared with rounded sand of similar size. When yield stress is expressed as a function of coarse particle concentration ratio (in situ/ maximum packing, i.e. Cs/C(max,s) ), the higher increase in yield stress due to coarse particle shape is normalized for sands with sizes larger than d50≈100μm.
    In terms of semi-empirical correlation performance, the Deltares correlation gave the best prediction, followed by the Thomas and the Lim et al. correlations. The use of a concentration ratio, C
    s/C(max,s), captures the effect of shape and improved the predictive capabilities of the Deltares and Thomas correlations.
    In conclusion, it appears that coarse particle contribution to yield stress increase is through an indirect physical interaction with aggregates in the fine-particle suspension, suggesting coarse particles are “rheologically inert” i.e. they simply occupy space. To improve upon the current understanding of the effect of coarse particle properties on yield stress, further investigations of smaller coarse particles (d
    50≤100μm) are required as well as tests involving polymodal suspensions.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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