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report 1 : Jan 5, 2010

Particle Residence Time in Column Flotation
Based on Cyclonic Separation
ZHOU Xiao-hua1,2, LIU Jiong-tian2
1Department of Mining Engineering, University of Kentucky, Lexington, KY 40506, USA
2School of Chemical Engineering and Technology, China University of Mining & Technology, Xuzhou, Jiangsu 221008, China
Abstract: The cyclonic static micro-bubble column flotation (FCSMC) is an effective separation device for fine particle
treatment. The high mineralization rate and short flotation time of this equipment can be attributed to its unique cyclonic
force field. It also has been observed that the presence of a cyclonic force field leads to a lower bottom separation size
limit and a reduction of unselective entrainment. The collection zone of the column is considered to consist of two parts,
a column separation zone and a cyclonic zone. Total recovery of the collection zone was developed. For our study, we
analyzed the particle movement in the cyclonic zone. Particle residence time equations for the cyclonic zone were derived
by force analysis. Results obtained in this study provide a theoretical foundation for the design and scale-up of the
FCSMC.
Key words: column flotation; cyclonic separation; residence time
CLC number: TD 94
1 Introduction
Column flotation can be designed using the same
principles applied to the design of chemical reactors.
This requires an understanding of flotation kinetics
and the residence time distributions of the solid and
liquid phases. Hence it is clear that in the design of
such columns a thorough investigation needs to be
made in order to determine the appropriate rate and
residence time distribution constants. An appropriate
model was developed in our study to determine the
residence time and describe the flow characteristics
of the solid and liquid phases in both column flotation
and cyclonic zones.
Several researchers have conducted residence time
distribution studies on column flotation cells. All the
models proposed describe the behavior of the collection
zone. However, data for the collection zone cannot
be obtained using liquid tracers since very little of
the feed water reports to this zone. In a study reported
by Dobby and Finch non-floatable manganese dioxide
was used as a tracer[1]; however, the concentration
of solids was 2%–3%, which was too low to highlight
any behavioral differences between different phases.
The most common approach to describe the collection
zone residence time distribution is to use a vessel
dispersion model. However, this model does not work
well for column scale-up because, although it has
been observed that for large columns the effect of the
degree of mixing on the predicted performance of the
column becomes less significant, it is, nevertheless,
inappropriate to use vessel dispersion numbers (D/uL)
greater than 0.2 because of the underlying assumptions
of the model[2]. The approximation for the vessel
dispersion model assumes that the end effects are
negligible, which is clearly not the case at low aspect
ratios. Secondly, in using the axial dispersion model
the assumption is made that there is no radial mixing.
This is unlikely to be valid in larger diameter columns.
This model therefore underestimates the mixing
in full-scale columns and leads to an overprediction
of the required column size[3]. The use of a
tanks-in-series model, or some other compartment
model, is therefore preferred.
Several researchers have derived correlations for
the solid phase dispersion coefficient (D) as a function
of the column diameter, the concentration of solids
and superficial gas rates[1, 3–4]. Mills, et al have