(457c) Direct Simulations of Flocculation In Sedimenting Solid-Liquid Suspensions

Direct simulations of flocculation in sedimenting
solid-liquid suspensions

Gravity-based separation (settling) is common practice in
many processes involving solids handling, specifically in mining and related
(mineral processing) applications. A widely used way to increase settling
rates, and to allow for gravity based separation of fine particles is to
promote aggregation so that flocs are formed that
fall faster through liquid than the primary particles. We study flocculation in
sedimenting solid-liquid suspensions numerically by
performing direct simulations with full resolution of the solid-liquid
interfaces and with full (two-way) coupling between liquid flow and solid
particle motion. In the simulations uniformly sized solid spheres are released.
They fall under the action of (net) gravity, they collide with one another
according to a hard-sphere model, they interact through the interstitial
liquid, and they tend to aggregate as a result of a square-well potential surrounding
each sphere. By means of the simulations we study how the settling velocity depends
on the strength of the square-well potential and the other key parameters in
the process: the solids volume fraction and the particle size. The observations
regarding settling velocities are interpreted in terms of the micro structure
of the suspension (radial and angular distribution functions), and in terms of
the floc size distribution and the fractal dimension
of the flocs.