Settling velocity of an aluminium-kaolinite floc

The settling velocity of a single floc made of well-characterized kaolinite coagulated with aluminium sulfate was measured as a function of floc diameter in order to reconsider the Tamboʹs floc density function. Our analysis focused on the exponent n in the scaling relation between the settling velocity and the floc diameter. A slight difference in n was observed when a different definition of floc diameter in the projection was adopted. That is, the projected area was found not to be proportional to the square of the scales measured in the projection such as the maximum distance in projected floc or the Feret diameter. This result agreed with the tendency reported by means of numerical simulation. The range of n obtained in the present study consistently corresponded with that reported in the computer simulation. Uniquely small values of n reported by Tambo and Watanabe (1979) for kaolinite-aluminium floc were not observed.