Methodological considerations for studying self-weight fluidization in a sedimentation column

Traditionally, the onset of fluidization has been examined in the laboratory by observing the formation of inflection points atop the descending mudline interface of a batch test. Recent preliminary experiments question the efficacy of inflection points for indicating the occurrence of fluidization. The utility of the mudline interface to uniquely identify the occurrence of fluidization is examined here. Alternative ways via laboratory and computational tools are employed to describe the temporal and spatial characteristics of fluidization.Detailed controlled experiments are performed for a pure kaolinite–water mixture under different initial concentrations and initial suspension heights. The experimental work is complemented with the use of an existing 1-D batch sedimentation model that accounts for the upward propagation of fluid and provides the variation of the mudline interface with time. Analysis of the experimental results shows that the onset of self-weight fluidization occurs in the early stages of a test, and not within the second falling rate region as other researchers have reported. Formation and upward propagation of fluidization pipes, typically with a diameter of 0.5–5 mm, are recorded. The numerical results further validate the experimental observations that self-weight fluidization cannot be always detected by observing the mudline interface. These findings agree with other results reported in the literature.