The theoretical investigation on the rate of gravity-induced flocculation of non-Brownian particles in quiescent media is presented in this paper. Based on the method of trajectory analysis and incorporating gravitational and interparticle forces (as described by DLVO theory), the stability diagrams for this gravity-induced flocculation of dilute colloidal suspension are provided. Depending on the values of the dimensionless parameters of λ (particle size ratio), ν (electromagnetic retardation parameter), κ (ionic strength), NG (the ratio of gravitational forces to van der Waals attractive forces) and NR (the ratio of electrostatic repulsion forces to van der Waals attractive forces), four distinct regions of flocculation are delineated in the stability diagram, (a) flocculation at the primary minimum of the total interaction energy profile; (b) flocculation at the secondary minimum of the total interaction energy profile; (c) an extremely narrow region of simultaneously flocculation at both the primary minimum and the secondary minimum of the total interaction energy profile; (d) a region of deflocculation where colloidal suspension remains stable. Two critical gravitational parameters (NG)Ci (i = 1, 2) are successfully applied to explain the occurrence of these four flocculation regions. Theoretical calculations of the capture efficiencies corresponding to these four regions are also presented. It is found that the colloidal suspension can be unstable at low and high gravitational forces, but stable at intermediate values of gravitational forces if the electrostatic repulsion is significant. ? 2001 Elsevier Science B.V.
Relation:
Colloids and Surfaces A: Physicochemical and Engineering Aspects 178 (1-3) , pp. 231-247
