Rheology and yielding transitions in mixed kaolinite/bentonite suspensions

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Kaolinite suspensions are known to have quite fast settling behaviour and Newtonian character, particularly at low concentrations, due to the non-swelling nature of their constitutive particles. On the other hand, bentonite is known for its swelling and interacting nature, which leads to the formation of a network structure, even at low concentrations. Therefore, both these clays are known to have significantly different rheological fingerprint. In this study, the yielding transitions in mixed kaolinite/bentonite suspensions have been investigated by varying the kaolinite/bentonite ratio and the total solid content. The detailed rheological analysis of these suspensions was carried out using amplitude sweep tests, frequency sweep tests, stress ramp-up tests and structural recovery tests.

The results showed that the kaolinite suspensions exhibited a two-step yielding behaviour in stress and amplitude sweep tests at higher solid content (≥ 35 wt%). On the other hand, the bentonite suspensions displayed a single-step yielding even at higher concentrations. In mixed kaolinite/bentonite suspensions, a clear transition between a single and two-step yielding behaviour was observed in steady and oscillatory tests as a function of kaolinite/bentonite ratio, for a particular total solid content. The structural recovery experiments showed that for mixed kaolinite/bentonite suspensions at lower total solid content, where two-step yielding was present, the structural recovery was lowest. Furthermore, these results showed that the rheological properties (i.e., moduli) of stable kaolinite/bentonite suspensions were completely recovered to their initial state, even after multiple shearing cycles. The settling column analysis displayed that a very small amount of bentonite was needed to stabilize the kaolinite suspensions, which is necessary for preparing stable clay based formulations.
Original languageEnglish
Article number106206
Number of pages10
JournalApplied Clay Science
Publication statusPublished - 2021


  • Bentonite
  • Kaolinite
  • Mixed suspension
  • Moduli
  • Particle size distribution
  • Rheology
  • Settling behaviour
  • Solid content
  • Two-step yielding


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