Extension of the compartment theory for hindered settling suspensions

Above a certain concentration, the fall of any particle in a suspension is observed to be hindered by the presence of other particles in its path. Several theories have been presented which describe the hindered settling nature of suspended particles using monoexponential equations. These theories were superseded by the theory proposed by Ping Tong et al., showing a biexponential nature of hindered settling in concentrated suspensions. In the present study, the associated film of water surrounding the sedimenting flocs of a concentrated aqueous suspension exhibiting hindered settling is considered to be an integral part of the sedimenting mass. Subsequently, a modified density for the flocs can be obtained. It is also assumed that the associated water phase around the flocs is in dynamic equilibrium with the external water phase, which constitutes the dispersing medium. This equilibrium shifts according to changes in concentration of the suspensions, which leads to the development of a three-compartment model. It satisfactorily describes the settling behavior of the concentrated suspensions of dry magnesium carbonate over the entire hindered settling range.