AU648353B2 - Flotation column - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT (Original) APPLICATION NUMBER:

LODGED:

COMPLETE SPECIFICATION LODGED:

ACCEPTED:

PUBLISHED:

RELATED ART: MULTOTEC

CYCLONES

NAME OF APPLICANT: ACTUAL INVENTOR(S): ADDRESS FOR SERVICE: MULTOTEC CYCLONES (PROPRIETARY) LIMITED MICHAEL HUGH MOYS KELVIN LORD AND COMPANY 4 Douro Place West Perth WA 6005 It INVENTION TITLE: "FLOTATION COLUMN" ftItc

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I ot DETAILS OF ASSOCIATED PROVISIONAL APPLICATIONS: NOS: The.following statement is a full description of this invention including the best method of performing it known to me/us:- M -2- This invention relates to the method of reducing axial mixing within a flotation column.

Large unbaff led columns are subject to severe axial 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 axial mixing. The Applicant has found that these baffles do not prevent axial mixing from taking place and that in some instances they enhance axial mixing.

Axial mixing 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 cleaners and not as roughers or scavengers.

The present invention seek to provide a method of reducing axial mixing within a flotation column.

According to the present invention there is provided a method of reducing axial mixing within a flotation column having a top and bottom and at least two separate upright passageways defined by baffle means having a top and a bottom said column bottom being below said baffle means bottom thereby defining a common zone below the baffle means, said method comprising: feeding a feed slurry in parallel separately into each separate passageway to a location below the top of the baffle means from respective slurry feed means each located Sbelow the top of the baffle means within each passageway; aerating the slurry in each passageway with air bubbles 0 0 on 00~00OO00~~0tW~9cVX YV 0 '~OI~,0$O'0t0 0 -3from aerating means spaced below each of said slurry feed means by directing said air bubbles upwardly through the slurry in each passageway and toward and past the respective slurry feed means to form a froth above the slurry in each passageway with the froth and slurry being separated from one another in each passageway by an interface; and maintaining the positions of the interfaces above'the feed means and below the top of the baffle means in each passageway.

The method may comprise the step of maintaining said interfaces substantially level with one another.

The positions of said interfaces are preferably maintained substantially level with one another by adjusting the position of one of said interfaces by adjusting the tailings rate and by adjusting the position of the other said interface or interfaces by controlling the feed rate i to the air bubbles and/or the feed rate of said slurry to Sthe other said passageway or passageways.

The method may include the step of feeding said slurry at S: 'ii t substantially the same level into each passageway from said feed means.

i i The said froth may overflow from said passageway into a common overflow zone.

S ,i The said slurry may be discharged from said passageways via a common tailings outlet.

The invention will now be described by way of non-limiting examples with reference to the accompanying drawings in Z which: ML M- 411 1 -4- 2 figure 1 is a cross-sectional side view of a flotation 3 column according to the invention; and 4 figure 2 is a perspective view of part of a flotation column according to another form of the invention; and 6 figure 3 is a cross-sectional side view on line III-III of 7 the flotation column shown in figure 2; and e M figure 4 is a graph showing the effect of the interface position relative to the baffles on the residence time distribution.

Referring to figure 1, a flotation column 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 froth overflow 20. The outlet 18 is provided with a valve 19.

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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 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 frother supply 38.

The positions of the interfaces 26 are controlled so as to be level with one another or as close to level with one another as possible. One of the interface levels is controlled by varying the tailings rate. The level of the other interface is controlled by controlling one or more of the following: the output from the bubble generator, I IIID L. r- L 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.

ii By ensuring that the interfaces 26 are located I below the top of the baffle 12, the column is effectively divided into two individual columns.

This eliminates recirculation or axial mixing 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 A 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

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relative to the position of the interfaces could be Ovaried. varied.

.i I Ii For each experiment a tracer (3 g of NaCI dissolved 1I in 200 ml water) was inserted into the slurry I 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 experiment 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 which is a measure of the gas rate, was kept constant at 0.75 cm/s for each experiment except for the last experiment where it was 0 cm/s.

i The results of the experiments are shown by way of five graphs in figure 3. 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; i- X t indicates the normalised residence time;

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T indicates the average residence time; and LINT S, 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 fraction of the tracer which spends a time between *a¢t 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 'elative 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 will be appreciated that many modifications and/or variations of the invention are possible without departing from the spirit or scope of the invention.

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Claims (7)

1. A method of reducing axial mixing within a flotation column having a top and bottom and at least two separate upright passageways defined by baffle means having a top and bottom said column bottom being below said baffle means bottom thereby defining a common zone below the baffle means, said method comprising: feeding a feed slurry in parallel separately into each separate passageway to a location below the top of the baffle means from respective slurry feed means each located below the top of the baffle means within each passageway; aerating the slurry in each passageway with air bubbles from aerating means spaced below each of said slurry feed means by directing said air bubbles upwardly through the slurry in each passageway and toward and past the respective slurry feed means to form a froth above the slurry in each passageway with the froth and slurry being separated from one another in each passageway by an interface; and maintaining the position of the interfaces above the feed means and below the top of the baffle means in each passageway.

2. The method of claim i, further comprising maintaining said interfaces substantially level with one another.

3. The method of claim 2, wherein the positions of said interfaces are maintained substantially level with one another by adjusting the position of one of said interfacis by adjusting the tailings rate and by adjusting the $1 I pI I s~s (II I 444* L I c i I' position of the other said interface or interfaces by controlling the feed rate of the air bubbles and/or the feed rate of said slurry to the other said passageway or passageways.

4. The method of any one of claims 1 to 3, further comprising feeding said slurry at substantially the same level into each passageway from said feed means.

The method of any one of claims 1 to 4, wherein said froth overflows from said passageway into a common overflow zone.

6. The method of any one of claims 1 to 5, wherein said slurry is discharged from said passageways via a common tailings outlet.

7. A method of reducing axial mixing within a flotation column substantially as hereinbefore described. DATED FEBRUARY 4, 1994 MULTOTEC CYCLONES (PROPRIETARY) LIMITED By their Patent Attorneys KELVIN LORD AND COMPANY PERTH, WESTERN AUSTRALIA i CI EL M