Agglomeration and filtration of colloidal suspensions with DVLO interactions in simulation and experiment

Abstract

Cake filtration is a widely used solid-liquid separation process. However, the high flow resistance of the nanoporous filter cake lowers the efficiency of the process significantly. The structure and thus the permeability of the filter cakes depend on the compressive load acting on the particles, the particles size, and the agglomeration of the particles. The latter is determined by the particle charge and the ionic strength of the suspension, as described by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. In this paper, we propose a combined stochastic rotation dynamics (SRD) and molecular dynamics (MD) methodology to simulate the cake formation. The simulations give further insight into the dependency of the filter cakes' structure on the agglomeration of the particles, which cannot be accessed experimentally. The permeability, as investigated with lattice Boltzmann (LB) simulations of flow through the discretized cake, depends on the particle size and porosity, and thus on the agglomeration of the particles. Our results agree qualitatively with experimental data obtained from colloidal boehmite suspensions.

Using Computational Steering to Explore the Parameter Space of Stability in a Suspension

“…In a detailed study we investigate how the interactions among the particles determine the structure of the so-called filter cake [51], i.e., the solid fraction accumulated at the filter plate. The porosity, and especially the permeability of the filter cake strongly determines the efficiency of the filtration process.…”

“…The suspended particles agglomerate in front of the filter and form the filter cake. Since the dynamics of the particles is not only governed by the hydrodynamics of the fluid, but also by their DLVO interaction, the density and the structure of the filter cake depend on the pH-value and the ionic strength [51].…”

“…We also study how an equillibration prior to the filtration process influences the structure of the filter cake [51]: if attractive forces are present in dilute suspensions, clusters form, which afterwards aggregate at the filter plane. In our simulations the filter is modeled by a closed boundary condition for the particles, which is fully permeable to the fluid.…”

“…In our simulations the filter is modeled by a closed boundary condition for the particles, which is fully permeable to the fluid. We use fully periodic boundaries for the fluid and drive the system either by applying a force to the fluid [18] or by moving the boundaries for the particles [51]. In the first case the force is applied to a limited region of the fluid so that the fluid is accelerated downwards and drags the particles with the flow towards the filter plane.…”

“…The results have mostly been published in a proceedings paper [18], but in this article we focus more on the technical details and give a more estensive description of the simulation method. Additionally, we comment on our work in progress, which will be published elsewhere together with our collaborators [51].…”