Porosity and interior structure analysis of pellet-flocs

Abstract

Pellet-flocs are the result of modified flocculation performance. They are spherically shaped and can reach several millimeters in size. Since pellet-floc aggregates are created from macroflocs and these from microflocs and these, in turn, from primary solid particles, it can be expected that the total porosity is composed of porosities resulting from spaces between all these sub-elements. Accordingly, micro- and macroporosity can be distinguished in the interior structure of pellet-flocs. Although considerable attention has been given to total aggregate porosity measurement, no reports can be found about the full morphological characteristics of different types of pores. Moreover, there is no single reliable method that can accurately obtain values for the respective fractions of pore volume (microporosity, macroporosity) within a relatively big floc aggregate. This work is an approach to probe the porosity within pellet-flocs at different size levels by combining the outcomes from different examination methods. Pellet-floc aggregates were investigated using the following techniques: free settling, light microscopy of resin-embedded microtome slices and scanning electron microscopy (SEM). The results confirmed that the biggest portion of porosity is composed of micropores in the size range of a few microns, which were first visible by SEM image analysis. Light microscopy of resin-embedded microtome slices is an accurate method to obtain so called macroporosity of a whole agglomerate with equivalent pore diameter above 50 μm. The study of free settling data revealed satisfactorily the total porosity of pellet-flocs. Finally, a multilevel porosity model of pellet-flocs could be obtained.