Effect of feed solid concentration on tailings slurry flocculation in a thickener by a coupled CFD-PBM modelling approach

Abstract

The flocculation technique has been proven fruitful for separating beneficiation wastewater from tailings slurry in the thickening process. The tailings flocculation is significantly affected by the feed solid concentration and flow characteristics, however, it is difficult to capture the local solid concentration and the resulting variation in flow characteristics by a conventional experimental approach. This paper thus employed a coupled Computational Fluid Dynamics-Population Balance Model (CFD-PBM) modelling approach to explore the effect of feed solid concentration on the flocculation performance in and around the thickener feedwell. The flocculation kinetics induced by polymer-bridging was incorporated into the PBM framework by aggregation and breakage kernels. The proposed model was validated against the experimental results in terms of liquid velocity and floc size distribution. The designed inner feedwell with deflectors has been demonstrated to have better flocculation performance. The effects of the feed solid concentration on the flow characteristics (e.g. effective viscosity of the slurry, and turbulence dissipation rate) and floc size distribution have been investigated. Results mainly show that the local solid concentration and effective viscosity of the slurry increase with feed solid concentration, while the mean floc size first increases and then decreases. A moderate feed solid concentration facilitates the flocculation performance. This study helps to understand the essential effect of feed solid concentration on the flow characteristics and flocculation performance, thereby guiding the flocculation-thickening process to achieve the sustainable use of beneficiation wastewater and mineral resources.