AU646329B2

AU646329B2 - Froth flotation of fine coal or mineral particles

Info

Publication number: AU646329B2
Application number: AU13190/92A
Authority: AU
Inventors: Christopher Hugh Barwise; John Wilson
Original assignee: Fospur Ltd
Current assignee: Fospur Ltd
Priority date: 1991-03-28
Filing date: 1992-03-25
Publication date: 1994-02-17
Anticipated expiration: 2012-03-25
Also published as: AU1319092A; GB9106746D0; GB2254021B; CA2064357A1; ZW5092A1; GB9206305D0; ZM1692A1; GB2254021A

Description

1

AUSTRALIA

646329 PATENTS ACT 1990 C n M P T, T F 9PFC VTCATIQN r 0 M P L E T FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: Actual Inventors: 0 0 0 Address for Service: 0 T aInvention Title: FOSPUR LIMITED Christopher Hugh Barwise and John Wilson SHELSTON WATERS 55 Clarence Street SYDNEY NSW 2000 "FROTH FLOTATION OF FINE COAL OR MINERAL

PARTICLES"

I I

I

The following statement is a full description of this invention, including the best method of performing it known to us:r-C. i- i FROTH FLOTATION OF FINE COAL OR MINERAL PARTICLES This invention relates to the froth flotation of fine particles and in particular to the recovery of coal from an aqueous slurry of coal fines also containing associated impurities as suspended fine solids by froth flotation, and to the beneficiation of fine mineral particles by froth flotation.

Coal as mined (run-of-mine-coal) contains a proportion of shale which when treated in water in a coal washery tends to revert to the original clay from which it was compressed in geological times. Separation of the coal from the fine shale and clay 10 particles presents considerable problems. In the case of mines where modern, mechanical extraction techniques are used, typically a proportion as high as about 20% of the run-of-minecoal consists of particles smaller than 0.5 mm. This fine "coal" typically has a substantial coal content but also a substantial shale content so it is important to make use of the coal content but also to remove shale from it. Modern coal preparation processes result in the fines (separated from coarser material) being in the form of aqueous slurries, In the United Kingdom the usual way of separating coal fines from shale fines in aqueous slurries is by means of froth flotation i i i 1--

I

followed by filtration.

In the froth flotation process the partially hydrophilic coal particles are treated with a surface active chemical compound, known as a "collector" so as to render the surface of the particles hydrophobic, so that they are attracted to air rather than water, and adding a so-called "frother", either mixed with the collector to form a so-called "froth flotation oil" or independently, to enable a froth of the required stability to be produced, and then aerating the aqueous suspension so that the coal is recovered in the froth so formed. The efficiency of this process is seriously affected by the presence of ultra-fine (of c 0 less than about 50 microns) matter (both coal and shale), often 00 present in significant proportions in the material requiring treatment.

44 The beneficiation of fine mineral particles by froth flotation is carried out in a similar manner, the particles of the mineral which it is desired to recover being rendered hydrophobic by the addition of a "collector" to an aqueous slurry of the mineral particles and particles of other minerals which it is not desired to recover, followed by the addition of a frother, and flotation S* of the particles of the desired mineral.

The largest particle present within a mass of mineral particles which are to be separated by froth flotation must be of size such I that the desired mineral particles will be physically released from the unwanted mineral particles and that the mass of each of the desired mineral particles does not exceed its force of attraction to an air bubble under the conditions of turbulence occurring in the aqueous suspension of mineral particles. It is therefore generally necessary to grind minerals so that the particles are sufficiently small for separation by an industrial froth flotation process. During the grinding process it is inevitable that some of the particles produced will be finer than intended and particles of the desired mineral which are too fine are generally difficult to recover by froth flotation. The size at which the difficulty is met will depend on a number of ,2 ,factors, including the specific gravity of the mineral which it is desired to recover, the degree of turbulence within the 15 aqueous suspension of mineral particles and the size range of the air bubbles in the suspension. Commonly, recovery of the desired mineral and rejection of unwanted minerals starts to deteriorate when the mineral particles are finer than about 10 microns, becoming very poor when the particles are finer than about 1 micron. These difficulties are commonly referred to 'as sliming problems.

GB patent application 2190310A describes a process in which coal fines are separated from shale fines by means of a froth flotation process and in which the particles of coal are treated with a hydrophobic polymer, such as a hydrophobic polyvinylalkyl

-L

4 ether which is highly selective as a flocculant for the coal fines in preference to the shale fines. GB patent publication 2212418A describes a similar process in which particles of a desired mineral are recovered from particles of an unwanted mineral in an aqueous slurry by means of froth flotation, after treatment with a predominantly hydrophobic polymeric flocculating agent which selectively flocculates the desired mineral particles.

It has now been found that alkyl acrylate polymers are particularly useful as selective flocculants in the froth flotation processes of the types described in GB patent publications 2190310A and GB 2212418A.

According to the invention in one aspect there is provided a process for separating particles of a desired material from particles of an undesired material, comprising adding a collector for the desired material and a frother and a polymer selected from homopolymers of alkyl acrylate, homopolymers of alkyl methacrylate, co-polymers of an alkyl acrylate or an alkyl methacrylate with maleic anhydride or vinyl pyrrolidone, and interpolymers of alkyl acrylate or alkyl methacrylate with an associated acrylic ester, to an aqueous slurry containing the particles of the desired material and the particles of the undesired material, and floating the particles of the desired material in a froth flotation cell.

4a The process of the invention may be used to recover coal fines from an aqueous slurry containing coal fines and shale fines, and also to recover fine particles of a desired mineral from an I ~c i t L- ^1 aqueous slurry containing both the particles of the desired mineral and fine particles of one or more undesired minerals. The process is useful when treating a slurry arising in the treatment of copper ores, copper nickel ores and ores containing copper and metals of the platinum group.

Examples of suitable polymers are alkyl acrylates in which the alkyl group may be methyl, ethyl, butyl, propyl, amyl, hexyl, heptyl or octyl (2-ethylhexyl). The polymer may also be an alkyl methacrylate having the same alkyl group. The polymer may be an interpolymer in which the methacrylate has an alkyl group such as methyl or ethyl or butyl, and associated acrylic esters.

To be effective in the method of the invention the selected polymer should have an average molecular weight in the range of about 10,000 to about 40,000, preferably about 20,000 to about 30,000. A preferred alkyl acrylate polymer is poly (n-butyl acrylate) which is commercially available as a highly viscous liquid from BASF United Kingdom Ltd under the trade mark ACRONAL LR 8820. The polymer may also be a copolymer of an alkyl acrylate or alkyl methacrylate and associated acrylic ester with a monomer such as maleic anhydride or vinylpyrrolidone. Mixtures may be used.

V.S "a 6 To be useful in the process of the invention the polymer must be dispersible in water. If the polymer is a liquid it can either be dispersed directly in the aqueous slurry or predispersed or dissolved in a carrier liquid. If the polymer is a solid it must be predispersed or dissolved in a carrier liquid. If desired a dispersant or emulsifying agent such as a non-ionic alkoxylated ester of a fatty acid may be used to aid dispersion of the polymer.

In another aspect the invention includes an additive composition when used to separate particles of a desired material from particles of an undesired material, the additive composition comprising a polymer selected from homopolymers of alkyl acrylate, homopolymers of alkylmethacrylate, copolymers of an alkyl acrylate or an alkyl methacrylate with maleic anhydride or vinyl pyrrolidone, and interpolymers of alkyl acrylate or alkyl methacrylate with an associated acrylic ester and a carrier liquid therefor.

When the process is used to recover coal fines the carrier liquid for the polymer may be a conventional collector as used in the froth flotation of coal, for example gas oil, Diesel oil, kerosene or other petroleum or coal-based distillates, or mixtures thereof. The polymer may also be dispersed or dissolved in a conventional froth flotation oil which consists of not only the collector but also the frother, and possibly other additives such as an emulsifier or dispersant.

6a When the process is used to recover a desired mineral from an undesired mineral the frother which is used in the conventional ~(R~i

O

CS

%h I_ I -ri--Xi froth flotation may act as the carrier liquid for the polymer.

Any of the known frothing agents used in the froth flotation of minerals, for example methylisobutylcarbinol, a propoxylated butanol or a polypropylene glycol, may be used as the carrier.

In the recovery of coal fines the amount of polymer used will usually be in the range of about 0.3g to about 200g per tonne of solids treated, and when the polymer is added as part of an additive composition containing the collector and the frother the additive composition will usually contain about 0.2% to about by weight of polymer, about 50% to about 90% by weight of collector or carrier liquid and about 10% to about 30% by weight of frother.

In the recovery of a desired mineral the amount of polymer used will usually be in the range of about 0.1g to about 10g per tonne of total mineral solids or about 0.5g to about 50g per tonne of the desired mineral, and when the frother acts as the carrier liquid for the polymer the additive composition will usually contain about 0.2% to about 25% by weight of polymer and about to about 99.8% by weight of frother.

Although in the recovery of a desired mineral the polymer is usually added to the frother as the polymer is soluble in the frother, if the polymer is soluble in the collector or another flotation reagent, such as a modifier (which modifies the collection or flotation), the polymer may be added to that reagent.

Variations in the structure of the alkyl acrylate polymers or alkyl methacrylate polymers, which vary their hydrophobicity, will vary the characteristics of the flocculation of the desired material and also the secondary characteristics of the flotation of the desired material.

For instance in the recovery of coal fines a poly (n-butyl acrylate) polymer which has a moderately high degree of hydrophobicity will strongly but selectively flocculate the ultra fine coal particles in a slurry, and will also yield a very dry froth compared to that obtained in a conventional froth flotation process.

It has also been found that an alkyl acrylate polymer or alkyl methacrylate polymer is particularly useful when it is used in conjunction with a hydrophobic polyvinylalkyl ether,'such as polyvinylethyl ether or polyvinylisobutyl ether, as a selective flocculant, and that when used together. the alkyl acrylate polymer or alkyl methacrylate polymer and the polyvinyl alkyl ether are complementary in their effect.

The following examples will serve to illustrate the invention in which parts are percent by weight unless otherwise indicated. In I 9 the examples, the froth flotation oil was a hydrocarbon oil acting as the collector and containing an emulsifier and a frother. The poly (n-butyl acrylate) used in Example I had an average molecular weight of 20,000 to 30,000, as did the polyalkylmethacrylate used in Example II. ACRONOL LR 8820 is a trade mark of BASF United Kingdom Ltd., as is LUTANOL Example I Two additive compositions were prepared as follows:proprietary froth flotation oil 98 poly (n-butyl acrylate) (ACRONOL LR 8820) 2 proprietary froth flotation oil 88 poly (n-butiy acrylate) (ACRONOL LR 8820) 2 polyvinylethyl ether (LUTANOL A25) Froth flotation tests were carried out on a coal/shale slurry in which the particle size of the solids was less than 700 microns and the solids content was 5.1% by weight, using compositions (1) and and as a control the proprietary froth flotation oil alone. In each test 0.062g. of the composition was added to 2.65 i litres of the slurry in a Denver DR cell turning at 1500 rpm.

After a conditioning time of 1 minute the air supply to the cell was turned on, and the froth which was produced was taken off for 160 seconds.

The results obtained are shown in Table I.

These results indicate the poly (n-butyl acrylate) polymer selectively flocculates the ultra-fine coal particles improving their separation from the ultra-fine shale and clay. When used on its own in the froth flotation oil the dry froth which it produces yields the minimum of clay in the coal product. When used in conjunction with the polyvinyl ethyl ether stronger frothing yields a higher recovery of coal with only slight increase in the clay content.

Example II An additive composition was prepared as follows: proprietary froth flotation oil polyalkylmethacrylate The polyalkylmethacrylate is an interpolymer of a mixed alkylmethacrylate and associated acrylic esters available from Rhone-Poulenc.

Comparative tests were performed in a coal flotation plant and filter using the composition and the oil alone. Samples of the coal slurry feed to the flotation were analysed together with samples of the froth, tailing products and filter cake. The recovery of combustible coal in the froth and the rejection of the ash into the tailing were calculated in the usual way. The results are set out in Table II and selectively flocculates the ultra-fine improving their separation from the ultra The filtration of the coal products is thus show that the polymer coal particles so fine shale and clay.

improved.

12 TABLE I

ADDITIVE

COMPOSITION

COAL

COAL PRODUCT ASH% TAILING ASH

COMBUSTIBLES

RECOVERY FEED ASH

CALCULATED

CONTROL

39.4 11.3 75.5 70.2 50.2 (1) 38.7 9.1 76.3 70.8 50.3 (2) 42.4 78.8 75.8 49.4 TABLE II CONTROL COMPOSITION DOSAGE RATE ml/minute 130 ASH IN FEED 45.3 j 46.5 COAL PRODUCT FROTH ASH) FILTER CAKE

ASH)

TAILING

ASH)

SOLIDS IN

FROTH

MOISTURE

IN FILTER CAKE

COMBUSTIBLE

RECOVERY 12.8 11.5 42.7 12.1 12.1 84.4 12.9 12.4 84.1 84.0 27.5 30.9 86.7 28.2 27.4 28.4 25.9 85.6 88.5 ASH REJECTION 84.6 87.2 L 83.7

COMBUSTIBLE

RECOVERY X ASH REJECTION 73.4 74.6 '74.1

Claims

1. Process for separating particles of a desired material from particles of an undesired material, comprising adding a collector for the desired material and a frother and a polymer selected from homopolymers of alkyl acrylate, homopolymers of alkyl methacrylate, co-polymers of an alkyl acrylate or an alkyl methacrylate with maleic anhydride or vinyl pyrrolidone, and interpolymers of alkyl acrylate or alkyl methacrylate with an associated acrylic ester, to an aqueous slurry containing the particles of the desired material and the particles of the undesired material, and floating the particles of the desired material in a froth flotation cell.

2. Process according to Claim 1, wherein the selected alkyl acrylate or alkylmethacrylate polymer has an average molecular weight of from about 10,000 to about 40,000.

3. Process according to Claim 1 or 2, wherein the selected alkylacrylate or alkylmethacrylate polymer has an average molecular weight of from about 20,000 to about 30,000.

4. Process according to any one of Claims 1 to 3, wherein the polymer is poly(n-butylacrylate). Process according to any one of Claims 1 to 3, wherein the polymer is a polyalkylmethacrylate.

6. Process according to any one of the preceding Claims, wherein the selected polymer is dispersible in water. ll^- p- -i 15 4 4 4 \*44I 'SA--

7. Process according to any one of the preceding Claims, wherein the polymer is a liquid and is dispersed directly in the aqueous slurry or predispersed or dissolved in a carrier liquid.

8. Process according to Claim 7, wherein the polymer is a solid and is predispersed or dissolved in a carrier liquid.

9. Process according to any one of the preceding Claims, used to treat an aqueous slurry containing coal fines wherein the carrier liquid for the polymer is the collector. Process according to Claim 9, wherein the carrier liquid comprises the collector, a frother, and an emulsifier or dispersant.

11. Process according to Claim 9 or 10, wherein the polymer is used in the proportion of about 0.3g to about 200g per tonne of solids in a coal slurry to be treated.

12. Process according to Claim 9, wherein the polymer is added in the form of an additive composition containing about 0.2% to about 15% by weight of the alkylated polymer, about 50% to about 90% by weight of collector or carrier liquid and about 10% to about 30% by weight of frother.

13. Process according to any one of Claims 1 to 8, used to recover a desired mineral from an aqueous slurry, wherein the carrier liquid for the polymer is the frother.

14. Process according to Claim 13, wherein the frother is methylisobutylcarbinol, a propoxylated butanol or a polypropylene glycol. 16 Process according to any one of the preceding Claims, wherein the polymer is used in the proportion of about 0.lg to about 10g per tonne of total mineral solids or about 0.5g to about 50g per tonne of the desired mineral.

16. Process according to Claim 15, wherein the polymer is added in the form of an additive composition which contains about 0.2% to about 25% by weight of the polymer and about 75% to about 99.8% by weight of frother.

17. Process according to any one of the preceding Claims, wherein the polymer is used in conjunction with a hydrophobic polyvinylalkyl ether.

18. Process according to Claim 17, wherein the hydrophobic polyvinylalkyl ether is polyvinylmethyl ether, polyvinylethyl ether or polyvinylisobutyl ether. V' 19. An additive composition when used to separate particles of a desired material from particles of an undesired material, the additive composition comprising a polymer selected from homopolymers of alkyl acrylate, homopolymers of alkylmethacrylate, copolymers of an alkyl acrylate or an alkyl methacrylate with maleic anhydride or vinyl pyrrolidone, and interpolymers of alkyl acrylate or alkyl methacrylate with an associated acrylic ester ,1 and a carrier liquid therefor. An additive composition according to Claim 19, wherein the polymer has an average molecular weight of from about 10,000 to about 40,000. X^^r~.L i -I~ 17

21. An additive composition according to Claim wherein the polymer has an average molecular weight of from about 20,000 to about 30,000.

22. An additive composition according to any one of Claims 19 to 21, comprising about 0.2% to about 15% by weight of the polymer, about 50% to about 90% by weight of collector or carrier liquid and about 10% to about by weight of frother.

23. An additive composition according to any one of Claims 19 to 21, comprising about 0.2% to 25% by weight of the polymer and about 75% to abouc 99.8% by weight of frother.

24. An additive composition according to any one of Claims 19 to 23, including a hydrophobic polyvinylalkyl ether. Process for separating particles of a desired material from particles of an undesired material, substantially as described and with reference to Example I or Example II.

26. An additive composition for use in separating particles of a desired material from particles of an undesired material, substantially as described and with reference to Example I or Example II. DATED This 8th Day of December 1993 FOSPUR LIMITED Attorney: IAN T. ERNST Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS