AU8934801A - Froth flotation - Google Patents

Description

*F b Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventor/s: Address for Service: Invention title: Anglo American Research Laboratories (Proprietary) Limited Jan Tjeerd Smit Kabamba Louis Whatum Jacques Frederik Malan James Anthony Jude Tumilty MADDERNS, 1st Floor, 64 Hindmarsh Square, Adelaide, South Australia, Australia FROTH FLOTATION A o* *t f fo ooo...

The following statement is a full description of this invention, including the best method of performing it known to us.

PatAU132) -2- 00': BACKGROUND OF THE INVENTION This invention relates to froth flotation.

In the processing of raw materials, such as rock or coal, it is common to effect a separation of the material into a fraction which contains a low •concentration of a desirable phase and a fraction which contains a high •concentration of a desirable phase. One well-known method to effect such separation is froth flotation. Froth flotation generally involves providing the material in a finely particulate, e.g. ground, form, contacting the finely particulate material with water and suitable flotation and other agents to form a pulp of chosen density, and contacting the pulp with finely dispersed gas bubbles in such a way that the desired phase is either selectively attached to the bubbles, or selectively left behind in the pulp. The phase, be it the froth phase or the pulp, will then have a higher concentration of the desired phase and may be separated and taken for further processing.

SUMMARY OF THE INVENTION According to the present invention, a method of froth flotation includes the steps of providing a material in particulate, preferably finely particulate, form, producing a pulp of the material in a liquid, generally water, contacting the pulp with gas bubbles, generally air, such that a desired phase or component is either selectively attached to the bubbles or selectively left behind in the pulp, and causing the gas bubbles to pass through a perforated barrier wherein the perforations are adapted to allow selective passage of gas bubbles, including gas bubbles to which particles are attached.

According to another aspect of the invention, apparatus for carrying out the above-described method includes a body, a chamber defined within the body, and a perforated barrier dividing the chamber into two sections, the perforations being adapted to allow gas bubbles, including gas bubbles to ~which particles are attached, in a froth flotation medium to pass selectively ~through the barrier.

20:. 0 BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described in more detail, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a schematic sectional side view of a first embodiment of apparatus of the invention; Figure 2 is a perspective view of a perforated barrier that can be incorporated into the apparatus of Figure 1; Figure 3 is a sectional side view of a second embodiment of apparatus of the invention; -4- Figure 4 is a graphic representation of value recoveries from a copper ore sample in a standard froth flotation column using normal frother dosages; Figure 5 is a graphic representation of value recoveries from a copper ore sample in an apparatus of the invention using normal frother dosages; Figure 6 is a graphic representation of value recoveries from a copper ore sample in a standard froth flotation column using higher than normal frother dosages; and Figure 7 is a graphic representation of value recoveries from a 15 copper ore sample in an apparatus of the invention using higher than normal frother dosages.

DESCRIPTION OF EMBODIMENTS The invention is concerned with'froth flotation and is characterised by the use of a perforated barrier which allows selective passage of particlecarrying gas bubbles through it. The perforations will typically be round with a diameter corresponding to between 0,5 and 3 mean bubble diameters, and more typically between 0,8 and 1,5 mean bubble diameters.

Generally, the barrier, which may be in the form of a plate, will have a thickness of no less than 1,5 mean bubble diameters and more typically no less than 2 mean bubble diameters.

In one form of the invention, two or more barriers are provided in the 5" chamber dividing the chamber up into more than two sections. With such an arrangement, a stepwise increase or decrease in the concentration of a desired component in the pulp relative to the position in the chamber may be achieved. It is desirable in such a case to allow some return flow of pulp be achieved. It is desirable in such a case to allow some return flow of pulp between the barriers since otherwise stacking of such barriers can effect no change in grade. This allowance may take the form of a few enlarged perforations. Thus, with such an arrangement multiple flotation stages can be provided in one chamber.

A baffling arrangement may be mounted on the side of the perforated barrier in which the froth flotation medium is produced, typically the underside thereof. Such baffling arrangement may be adapted to minimise lateral movement of the bubbles before passage through the barrier perforations. In this manner, particle detachment from the bubbles is minimised.

The perforated barrier may be mounted within a tubular member or drafting tube. Such a tube would typically have a diameter less than that of the column body such that an annular space is defined between the outer wall :o of the draft tube and the inner wall of the outer body. Such an arrangement ~allows bubbles to rise together with the pulp medium from which the desirable component is recovered within the draft tubes, whilst allowing the pulp medium to return via the annular space provided around the draft tube.

~The conditions used for the froth flotation will vary according to the nature of the material being treated and other such factors. The invention has particular application to the froth flotation of mineral-bearing ores and materials. Generally in such cases the liquid medium will be water and the 25 gas bubbles will be air bubbles.

A first embodiment of the invention will now be described with reference to •oooo S" Figure 1 of the accompanying drawings. Referring to Figure 1, apparatus for carrying out a froth flotation comprises a vertical vessel 10 having a perforated plate 12 extending across the vessel and dividing it into an upper zone 14 and a lower zone 16. A froth flotation medium is produced in the zone 16. Particle-carrying gas bubbles 18 rise and tend to concentrate on the underside of the perforated plate 12, so as to provide for greater contact with particles in the froth flotation medium. The perforations -6are of such dimension that they allow selective passage of the particlecarrying gas bubbles therethrough and into the zone 14. If some of the perforations of the plate 12 are enlarged, some return flow of pulp from the zone 14 to the zone 16 is possible.

Referring to Figure 2 of the accompanying drawings, the perforated plate 12 includes a baffling arrangement 20 depending from below its underside 22. The baffling arrangement 20 defines an array of passages 24 through which the gas bubbles rise. The baffling arrangement 20 minimises the lateral movement of the gas bubbles 18 before passage through the perforated plate 12, hence minimising detachment of the particles from the gas bubbles 18.

A second embodiment of the invention is shown in Figure 3 of the accompanying drawings. Referring to Figure 3, apparatus for carrying out a froth flotation comprises a vertical vessel 30 including a first draft tube 32 having a perforated plate 34 extending across it and dividing it into a first upper zone 36 and a first lower zone 38, and a second draft tube including a perforated barrier 42 extending across it and dividing it into a second upper zone 44 and a second lower zone 46.

A froth flotation medium is produced in the first lower zone 38. Particlecarrying gas bubbles (not shown) rise through the first draft tube 32 where they tend to concentrate on the under side of the perforated plate 34. Once again, the perforations are of such a dimension that they allow selective passage of the particle-carrying gas bubbles therethrough and into the first upper zone 36.

The bubbles then rise from the first upper zone 36 through the second lower zone 46 whereupon they concentrate on the underside of the perforated plate 42. Once again, the perforations of the second plate 42 are of such a dimension that they allow selective passage of the particlecarrying gas bubbles therethrough and into the second upper zone 44. The -7perforations of the second plate 42 may be the same or different to that of the first plate 34.

The particle-carrying gas bubbles then rise towards the upper region 48 of the vessel 30 where they form a froth phase which can be recovered via the weir 50. The froth flotation medium or pulp medium may then pass downwards through the annular spaces 52 or 54 defined around the first and second draft tubes 32 and 40, respectively, to be contacted by further gas bubbles rising towards the froth phase 48.

As a result of using two perforated plates or barriers 34 and 42, a stepwise increase or decrease in the desired component or phase in the pulp is effected.

In order to investigate the efficacy of recovering valuable minerals from an ore using an apparatus of the invention, the apparatus of the invention was compared to a standard froth flotation column. The results of the comparative tests are set out graphically in Figures 4 to 7 of the S. accompanying drawings. The apparatus of the invention incorporated a 0 double barrier arrangement as shown in Figure 3, having a total volume of about 10 litres. A standard froth flotation column of the same height with a S. similar total volume was used for comparative purposes. Air addition flow rates and reagent additions were kept constant in this comparative test, which was carried out on a sample of copper ore from Mantos Blancos, Chile.

Figure 4 shows graphically the results of a froth flotation process carried o:out in the standard column at normal frother dosages, whilst Figure 5 sets out the comparative results obtained using the apparatus of the invention at normal frother dosages. As can be seen from these graphs, far superior concentrate grades where achieved in the double barrier column of the invention (Figure 5) when compared with the comparative figures of the standard flotation column (Figure As the bubble diameters were somewhat larger than the perforation diameter, the rate of concentrate -8recovery in the double barrier column of the invention was slower than for the conventional column.

Accordingly, more frother reagent was added to both the columns and the test repeated, the results of which are set out in Figures 6 and 7. The use of a higher frother dosage resulted in smaller bubbles than the perforation diameter of the double barrier column of the invention. Accordingly, as can be seen from Figure 7, copper recoveries were far superior when compared to the figures of the standard column (Figure at substantially the same final concentrate grade.

As can be seen from the above test results, it has been found that using an apparatus as described above results in enhanced recoveries of a targeted component and/or an increased concentration of such component in a product stream when compared with conventional froth flotation apparatus.

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Claims (14)

1. A method of froth flotation includes the steps of providing a material in particulate form, producing a pulp of the material in a liquid, contacting the pulp with gas bubbles such that a desired phase or component is either selectively attached to the bubbles or selectively left behind in the pulp, and causing the gas bubbles to pass through a perforated barrier wherein the perforations are adapted to allow selective passage of gas bubbles, including gas bubbles to which particles are attached.

2. A method according to claim 1, wherein the gas bubbles are caused to pass through more than one perforated barrier so as to effect a stepwise increase or decrease in the concentration of the desired *"phase or component in the pulp. 4*

3. A method according to claim 1 or claim 2, wherein the particulate material is in a fine particulate form.

4. A method according to any one of the preceding claims, wherein the particulate material is derived from a mineral-bearing ore.

5. A method according to claim 4, wherein the liquid is water and the gas bubbles are air bubbles.

An apparatus for carrying out a method of froth flotation, the 25 apparatus comprising a body, a chamber defined within the body, and a perforated barrier dividing the chamber into two sections, the perforations being adapted to allow gas bubbles, including gas bubbles to which particles are attached, in a froth flotation medium to pass selectively through the barrier from one section to another.

7. An apparatus according to claim 6, comprising two or more perforated barriers for effecting a stepwise increase or decrease in the concentration of a desired phase or component in the froth flotation medium or a pulp from which it is derived relative to its position in the chamber.

8. An apparatus according to claim 6 or claim 7, wherein the perforations are substantially round with a diameter corresponding to between 0,5 and 3 mean bubble diameters.

9. An apparatus according to claim 8, wherein the diameter of the perforations corresponds to between 0,8 and 1,5 mean bubble diameters.

10. An apparatus according to any one of claims 6 to 10, wherein the or each perforated barrier is in the form of a plate having a thickness of no less than 1,5 mean bubble diameters.

-11. An apparatus according to claim 10, wherein the plate has a thickness of no less than 2 mean bubble diameters.

12. An apparatus according to any one of claims 6 to 11, wherein the or each perforated barrier includes a baffling arrangement for minimising lateral movement of gas bubbles passing therethrough S 25 so as to minimise particle detachment.

13. An apparatus according to any one of claims 6 to 12, wherein the or S° each perforated barrier is mounted within a tubular member located within the body, the body and tubular member defining a return passage for the froth flotation medium so as to contact further gas bubbles prior to passing through the or each perforated barrier once again. -11-

14. An apparatus according to any one of claims 6 to 12, wherein the or each perforated barrier includes a number of larger perforations so as to provide for return of the froth flotation medium therethrough so as to contact further gas bubbles prior to passing through the or each barrier once again. Dated this 12th day of November 2001. ANGLO AMERICAN RESEARCH LABORATORIES (PROPRIETARY) LIMITED By its Patent Attorneys MADDERNS S .e e.. S, ***ee *RO**