Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2~5~520
This invention relates to a flotation column and to
a method of separating particulate material in a
flotation column.
Large unbaffled columns are subject to severe a~ial
mixing or recirculation. It has generally been
assumed that such columns should be baffled by
vertical baffles located wholly within the slurry
phase to reduce a~ial mixing. The Applicant has
found that these baffles do not prevent a~ial
mi~ing from taking place and that in some instances
they enhance axial mixing.
Axial mi~ing results in a reduced residence time of
some of the particulate material within the column
leading to a poor recovery rate. It is for this
reason that flotation columns have generally only
been used as clea~ers and not as roughers or
scavengers.
It is an object of this invention to provide a
flotation column and a method of separating
2(~ 20
particulate material which at least reduce axial
mi~ing associated with prior art flotation
columns.
According to a first aspect~of the invention,
there is ~;rovided a flotation column for
separating particulate material includes at least
two separate passageways within each of which
slurry is in use separated from froth by an
interface, feed means within each passageway for
feeding the slurry into each passageway below the
interface, bubble generating means located below or
within the passageways, and at least one tailings
outlet below the bu'oble generating means.
In the preferred form of the invention control
means is provided for controlling the positions of
the interfaces.
In one form of the invention the control means may
be valves for manipulating the flow of fluid or
particulate material to or from the column.
The froth zones may merge to form a common froth
zone.
The separate passageways may be formed by at least
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one baffle. The baffle may extend from above the
outlet so that the passageways have a common
outlet. The top of the baffle may terminate at
the froth overflow zone or above at least part of
the froth overflow zone.
The separate passageways may include at least one
closable opening through which the passageways can
communicate with one another. Circulation may take
place through this opening. The circulation can
be used to control the relative levels of the
interfaces. The opening may be closable by a gate
located in the baffle.
According to another aspect of the invention a
flotation column for separating particulate
material includes at least one continuous baffle
which creates at least two separate passageways in
each of which slurry is in use separated from froth
by an interface, the top of the baffle terminating
at the froth overflow zone or above at least part
of the iroth overflow zone.
According to another aspect of the invention a
method of separating particulate material within a
flotation column having at least two separate
passageways includes the step of creating a slurry
phase and a froth phase within each passageway,
with the phases in each passageway being separated
by an interface located within each passageway.
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The method preferably includes the step of 2 ~ 5~5 2 0
controlling the positions of the interfaces within
each passageway by manipulating the flow of fluid
or particulate material to or from the column. In
one form of the invention the position of one of
the interfaces is controlled by controlling the
flow of slurry from the column, and the positions
of the other interfaces are controlled by allowing
circulation between a closable opening between the
passageways or by adjusting the performance of the
bubble generating means.
The invention will now be described by way of a
non-limiting e~amples with reference to the
accompanying drawings in which:
igure 1 is a cross-sectional side view of a
flotation column according to the
invention; and
igure 2 is a perspective view of part of a
~lotation column according to another
form of the invention; and
igure 3 is a cross-sectional side view on line
III - III of the flotation column shown
in figure 2; and
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2~ S20
igure 4 is a graph showing the ef~ect of the
interface position relative to the
ba~fles on the residence time
distribution.
Re~erring to ~igure 1, a flotation column 10
includes a baffle 12 which divides part of the
column 10 into two separate passageways 14 and 16.
The passageways have a common tailings outlet 18
and a common ~roth overflow 20. The outlet 18 is
provided with a valve 19.
Each passageway has a slurry phase 22 separated
from a froth phase 24 by an interface 26.
Furthermore, each passageway has its own slurry
supply 28 which can be controlled by a valve 30.
In addition each passageway has its own bubble
generator 32. Each bubble generator is connected
to an air supply 34, a water supply 36 and a
irother supply 38.
The positlons o~ the inter~aces 26 are controlled
so as to be level with one another or as close to
level with one another as possible. One of the
inter~ace levels is controlled by varying the
tailings rate. The level of the other inter~ace is
controlled by controlling one or more o~ the
~ollowing: the output from the bubble generator,
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2~S~O
the slurry supply to the passageways or the
circulation between the passageways through
closable openings (not shown) in the baffle.
Although also not shown, probes are provided for
monitoring the pressure a short distance below the
interfaces. The outputs from the probes may be
used automatically to vary the bubble and/or slurry
feed to the passageways. Thus the interfaces can
be kept level with one another automatically.
Various other methods could of course be used for
sensing the interface level in each passageway.
8y ensuring that the interfaces 26 are located
below the top of the baffle 12, the column is
effectively divided into two individual columns.
This eliminates recirculation or a~ial mi~ing of
the slurry between the two passageways.
Referring now to figures 2 and 3 in which the same
numerals refer to the same parts of figure 1, the
top 12.2 of the baffle 12.1 terminates at the top
of the froth overflow 20.2 of the flotation column
10.1.
The applicant conducted five experiments using a
flotation column in which the height of baffles
relative to the position of the interfaces could be
varied.
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2~5'~
For each experiment a tracer (3 g of NaCl dissolved
in 2~0 ml water) was inserted into the slurry
supply. The tracer concentration was then measured
by a conductivity probe at the tailings outlet of
the column to determine the residence time
distribution of the tracer within the column. In
the first e~periment the interfaces were located
four centimetres above the top of the baffle. In
the second experiment the interfaces were level
with the top of the baffle, thereafter the
interfaces were 1 cm; 3,5 cm and 1 cm respectively
below the top of the baffle. The gas superficial
velocity (JG), which is a measure of the gas rate,
was kept constant at 0.75 cm/s for each experiment
except for the last e~periment where it was 0 cm/s.
The results of the experiments are shown by way of
five graphs in figure 4. The top graph relates to
the first experiment and the bottom graph to the
fifth experiment. In figure 4, E(X) indicates the
residence time distribution; t indicates time;
X = t indicates the normalised residence time;
T indicates the average residence time; and LINT -
LBAFF is the difference in height between the
interfaces and the baffle. The residence time
distribution E(X) is defined as E(X)dX which is the
~raction of the tracer which spends a time between
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2~ o
X and XtdX in the column where dX is a small time
increment.
The experiment showed that the residence time
distribution of the tracer within the column
improved as the height of the baffle was raised
relative to the interfaces. The time taken for the
fastest moving tracer to move from the slurry inlet
to the tailings outlet increased, and the spread of
the distribution was reduced as the height of the
baffle was raised relative to the interfaces. Thus
more particulate material passed through the column
at residence times which were close to the average
residence time.
The applicant believes that a substantial
improvement in residence time distribution and
hence column recovery can be obtained in columns in
which the interfaces are located below the top of
the baffles. Furthermore the applicant believes
that these columns will be able to be used as
roughers and scavengers.
It wili be appreciated that many modifications
and/or variations of the invention are possible
without departing from the spirit or scope of the
invention.
