(37e) Aggregation and Breakage Dynamics of Alumina Particles Under Laminar Shear By CFD-DEM Simulations

Particle recovery from suspension holds significant importance across various industries including wastewater treatment, food engineering, ceramic powder processing, and mineral processing. An illustrative application is the aggregation of fine valuable mineral particles in mineral processing to facilitate their collection via froth flotation. Thus, effective control of particle aggregation and breakage dynamics is key in powder and particle processing, given that the aggregate characteristics influence product grade and process efficiency [1]. Various control strategies can be employed to manipulate interparticle interactions, including adjusting suspension pH, using salts, adding surface modifiers like polymers, or applying shear forces to suspensions [2]. However, observing and quantifying particle dynamics in suspensions experimentally poses challenges due to the rapid particle aggregation and breakage, usually taking place within microseconds. Particle-based simulations provide a promising approach for studying particle dynamics, enabling direct observation and quantification of aggregate formation and breakage in suspensions [1].

Here, Computational Fluid Dynamics – Discrete Element Method (CFD-DEM) are used to explore how laminar shear affects particle aggregation and aggregate breakage, taking into account interactions among particles and between particles and the surrounding fluid. The steady-state aggregate size distribution closely matches the experimental data (Figure 1 [1, 3]), thereby validating CFD-DEM simulations. The evolving aggregate size and structural characteristics are quantified as they undergo concurrent aggregation and breakage within a linear velocity gradient found in a Couette flow cell, ranging from individual spherical particles to large aggregates, showing strong agreement with experimental observations. The temporal evolution of the aggregate number concentration aligns well with first-order aggregation theory [4] at low shear rates. However, increasing shear rates, increase the deviation from the theoretical collision kernel, due to the reduced collision efficiency at these conditions. Particle dynamics are characterized by three distinct regimes based on shear rate and aggregate size: pure breakage, breakage and restructuring, and restructuring and aggregation (Figure 2 [3]). A novel breakage rate equation is proposed, capturing the transition from the breakage and restructuring regime to the pure breakage limit [3].

References

1. Kushimoto, K., Ishihara, S., Pinches, S., Sesso, M.L., Usher, S.P., Franks, G.V., and Kano, J., Development of a method for determining the maximum van der Waals force to analyze dispersion and aggregation of particles in a suspension. Advanced Powder Technology, 2020. 31(6): p. 2267-2275. https://doi.org/10.1016/j.apt.2020.03.021.

2. Franks, G.V. and Zhou, Y., Relationship between aggregate and sediment bed properties: Influence of inter-particle adhesion. Advanced Powder Technology, 2010. 21(4): p. 362-373. https://doi.org/10.1016/j.apt.2010.02.007.

3. Zeng, L., Franks, G.V., and Goudeli, E., Aggregation and breakage dynamics of alumina particles under shear by coupled Computational Fluid Dynamics – Discrete Element Method. Journal of Colloid and Interface Science, 2024. 661: p. 750-760. https://doi.org/10.1016/j.jcis.2024.01.210.

4. Swift, D.L. and Friedlander, S.K., The coagulation of hydrosols by brownian motion and laminar shear flow. Journal of Colloid Science, 1964. 19(7): p. 621-647. https://doi.org/10.1016/0095-8522(64)90085-6.