Gravity-induced flocculation of binary particle suspensions

A theoretical investigation on the gravity-induced flocculation rates of non-Brownian/Brownian particles in quiescent media is provided in the present paper. Based on the method of trajectory analysis and incorporating gravitational and interparticle forces (as described by the DLVO theory), the effects of the particle size ratio and the reduced density ratio on the capture efficiencies of non-Brownian/Brownian particles in binary suspensions are systematically studied. We find that the capture efficiencies of non-Brownian/Brownian particles will always increase with the increase of either the particle size ratio or the reduced density ratio under the condition of high ionic strength where the electric double layer repulsive force diminishes. When the electric repulsive force is presented, we find that the dispersions will become unstable at some intermediate particle size values, and those non-Brownian/Brownian particles will not become flocculated until a critical ionic strength is reached for a fixed reduced size ratio. We also confirm that the Brownian diffusion behavior of particles can decrease their flocculation rates under the strong Brownian/weak gravity condition.