(333d) Modelling Particle Aggregation and Breakage in Suspensions By Coupled CFD-DEM

Particle aggregation and dispersion in suspensions are two important processes in the mineral industry because the particle characteristics (e.g., size structure, shape) highly influence the flow properties of suspension (e.g., viscoelasticity, particle settling rate and shear stress), which further affect downstream product grade, recovery and process efficiency. Especially in froth floatation, the physical characteristics of aggregates can determine the collection of valuable minerals. Therefore, the control of dispersion and aggregation of fine particles is significant for the mineral processes. Changing pH, adding surface modifiers, or applying shear force play an important role in controlling aggregate size and structure (Franks and Zhou, 2010). Although much research has focused on aggregate dynamics in the suspension, the mechanisms are still not fully understood due to the difficulties of monitoring aggregate behaviour over very short time steps. Therefore, simulation and modelling of particle aggregation and dispersion in suspensions is becoming a imperative to study aggregate dynamics.

In this work, two numerical models, Discrete Element Method (DEM) and Computational Fluid Dynamics (CFD), were coupled to simulate the effect of shear and pH on aggregate dynamics in suspension. This simulation describes the motion of particles and fluid, particle-particle interaction, and particle-fluid interaction. The structural properties of aggregates (cumulative size distribution, fractal dimensions, average size, etc.) were determined when the aggregate dynamics reached a stable condition in the simulation. Accordingly, a higher shear rate increases the chances of particle collision, but also leads to faster aggregate breakage, in agreement with Kushimoto et al. (2020). Aggregates with higher fractal dimension have a dense, spherical-like structure with more neighbour particles, and are much harder to break into smaller fragments.

References

Franks, G. V.; Zhou, Y., Relationship between aggregate and sediment bed properties: Influence of inter-particle adhesion. Advanced Powder Technology 2010, 21 (4), 362-373.

Kushimoto, K.; Ishihara, S.; Pinches, S.; Sesso, M. L.; Usher, S. P.; Franks, G. V.; 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), 2267-2275.