AU744544B2 - Process for improving recovery of copper, nickel and PGM bearing minerals - Google Patents

Description

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AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

Name of Applicant: BOC GASES AUSTRALIA LIMITED, A.C.N. 000 029 729 Actual Inventors: Andrew James Haigh NEWELL, David William CLARK and Henry Nhlanhla GUMEDE Address of Service: BALDWIN SHELSTON WATERS MARGARET STREET \SYDNEY NSW 2000 Invention Title: "PROCESS FOR IMPROVING RECOVERY OF COPPER, NICKEL AND PGM BEARING MINERALS" Details of Associated Provisional Application No. PO 7882 dated 14 July, 1997 The following statement is a full description of this invention, including the best method of performing it known to us:- TECHNICAL FIELD The present invention relates to froth flotation separation of minerals and in particular froth flotation of chalcopyrite, pentlandite, chalcocite, and platinum group metal (PGM) bearing minerals.

BACKGROUND ART Platinum group metals occur in mainly two forms, as discrete minerals and in solid solution in base-metal sulphides.

PGMs and PGM minerals are often associated with nickel and copper ores however this is not always the case. In South Africa, for example, PGMs are recovered from both 10 Merensky and UG-2 ores.

The predominant base-metal sulphides in Merensky ore are chalcopyrite, pentlandite, pyrrhotite and pyrite. Pentlandite, pyrrhotite and pyrite contain various amounts of platinum, palladium and rhodium.

UG-2 ore contains a high chromite content (60-90%) along with 5-25% of gangue 15 silicates, orthopyroxene and 5-15% plagioclase. Trace amounts of base-metal sulphides occur mainly interstitially to the chromite grains. The sulphides are mainly pentlandite, pyrrhotite, chalcopyrite, cobalt-pentlandite and millerite. The PGMs are usually associated with the base metal sulphides and are normally included in or attached to the sulphide grains.

The platinum group metals including platinum, palladium, rhodium, osmium, iridium and ruthenium are recovered by traditional flotation methods ie. crushing, milling and flotation. Many producers, for example in South Africa, re-grind and float the flotation tail in a so called MF/MF circuit ie. mill/float, mill/float.

-3- Of course the primary objective of these conventional flotation processes is to increase the recovery ofPGMs. Unfortunately, however, the conventional processes have several problems.

The first of these is the chromite content in the final flotation concentrate. As chromite has a relatively high density and is brittle in nature, it is inevitably over-ground in a milling circuit This results in a fine chromite being entrained in the final concentrate with serious implications in the downstream smelting process when the levels of Cr20 3 are excessive. Indeed the maximum permissible chromite content in the final concentrate is preferably 3-4% depending upon the smelter.

Conventional flotation processes also have difficulty in separating PGMs while maintaining an acceptable grade. The flotation rates/kinetics of sulphide minerals are slow.

To achieve an acceptable grade/recovery, the conventional flotation circuits have extensive S. stages of cleaning and re-cleaning.

The order of sulphide mineral bulk flotation response in descending order are 15 chalcopyrite, pyrite, pentlandite and pyrrhotite.

Lastly, the effect of talc can vary from mild to severe depending upon the degree of alteration of the ore. Moderate quantities of talc may be handled by the addition of a depressant such as CMC, however large quantities of talc create serious difficulty.

Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.

It is an object of the present invention to overcome at least someof the disadvantages of the prior art or provide a commercial altemative to the prior art.

-3a DISCLOSURE OF 'TEE INVENTION The present invention provides a process* for the recovery of valuable sulphide mineral ores comprising providing a slurry of said ore, conditioning said slurry with suitable activators, collectors, frotler and/or depressants -ad subjecting the conditioned -4slurry to further conditioning with an inert/non-oxidising gas in a quantity conducive to improving separation of the sulphide minerals from the remainder of said ore, and subsequently subjecting said slurry to a final flotation treatment with a gas having a higher oxygen content than said inert/non-oxidising gas.

The present process is suitable for recovery of various base metal sulphide minerals.

It is particularly suitable for recovery of chalcopyrite, chalcocite, pentlandite, pyrrhotite and pyrite, and PGM bearing sulphide minerals.

Nitrogen is the preferred inert/non-oxidising gas however other inert/non-oxidising gases may be used including argon, neon or carbon dioxide, methane, propane, ethane and 10 mixtures thereof.

In a preferred embodiment, the nitrogen gas is added to the slurry prior to the reagent conditioning stage. In another embodiment, the nitrogen is added to the slurry after the reagent conditioning stage but prior to the final flotation treatment.

Preferably air is used as the flotation gas in the final flotation treatment however other gases which have a higher oxygen content than the inert/non-oxidising gas used in the conditioning step, may be used.

In still a preferred embodiment, the flotation maybe conducted over the several stages to remove a PGM bearing chalcopyrite followed by a PGM bearing pentlandite followed by PGM bearing a pyrrhotite and pyrite.

The applicants have found that nitrogen injection into the slurry not only increases recovery of PGMs and PGM minerals but also improves recovery of the base metals eg.

nickel, copper, which are intimately associated with the PGMs.

The improved process not only improves recovery but also simplifies the equipment necessary for recovery of PGMs. As mentioned above existing technology uses multiple rougher/cleaner flotation stages or the so called MFMF circuit (mill/float, mill/float) to achieve an acceptable concentrate. Use of the present invention avoids or at least reduces the need for such complex flotation circuitry.

In still a further embodiment of the present invention, as well a conditioning with the inert/non-oxidising gas prior to the final flotation step, an initial flotation using the inert/non-oxidising gas may be included.

In still another embodiment, the inert/non-oxidising gas conditioning or flotation step may be included in a milling circuit such that the slurry leaves the milling circuit, is conditioned and/or floated using an inert/non-oxidising gas and the resultant tailings return 10 to the milling circuit and subsequently to the final treatment.

In another embodiment, the slurry can be conditioned with the inert/non-oxidising gas prior to its entry into a series of flotation cells. The first group of cells may use nitrogen as a flotation gas with the remainder using air as a flotation gas.

Such an arrangement may be provided in rougher/scavenger circuit or in the cleaner 15 circuits of a mineral recovery plant.

The applicant has surprisingly found that the use of such a discrete conditioning period in which the slurry is intimately contacted with an inert/non-oxidising gas improves the recovery of both the base metal sulphides eg chalcopyrite, pentlandite, pyrrhotite and pyrite along with the PGMs and PGM minerals associated therewith.

Unless the context clearly requires otherwise, throughout the description and the claims, the words 'comprise', 'comprising', and the like are to be construed in an inclusive as opposed to an exclusive or exhaustive sense; that is to say, in the senSe of "including, but not limited to".

-6- BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a simplified flow diagram of a process for the treatment of PGM mineral bearing ores according to a first embodiment of the present invention, and Figure 2 is a simplified flow diagram of a process for the treatment of PGM mineral bearing ores according to a second embodiment of the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION In the first embodiment shown in figure 1, the PGM bearing ore is milled, normally 10 in a liquid, in the milling circuit 10. A suitable liquid diluent eg water is then added to this milled material and the resultant slurry passed through a separation means 20 eg. cyclone bank. The overflow from the cyclone ie. slurry with particles of the required size, is then fed to the reagent conditioning stage 30. In this stage one or more of a suitable activator 32 CuSO 4 a collector 34 preferably a xanthate eg SIBX, a frother 36 such as MIBC and a S 15 suitable depressant 38 such as dextrin or other organic colloids may be added either separately or simultaneously.

The conditioned slurry is then transferred to the inert/non-oxidising gas conditioning stage where the slurry is conditioned with an inert/non-oxidising gas, in this case nitrogen, for a suitable period preferably between 1 and 30 minutes and most preferably between 2 and 10 minutes prior to flotation.

The conditioning of the slurry with inert/non-oxidising gas may be conducted in a range of equipment including mechanically agitated conditioner vessel(s), gas agitated vessel(s) (Pachua), flotation cell(s), modified flotation cell(s) and slurry pipe line, hydrocyclones or modified versions thereof.

-7- The nitrogen conditioned slurry is then transferred to the flotation stages 50 where flotation is carried out with air as the carrier gas in a number of stages. In a preferred embodiment, the flotation stages may be arranged to selectively remove various base metal sulphide minerals which are intimately associated with the PGM mineral. For example, the flotation stages may be arranged to remove in order PGM bearing chalcopyrite, followed by PGM bearing pentlandite followed by PGM bearing pyrrhotite and pyrite.

The applicant has found that dosing the slurry with inert/non-oxidising gas eg nitrogen increases the recovery of both the base metal sulphide and the associated PGM minerals. In the case of Merensky ores, for example, there appears to be a direct 10 correlation between nickel, copper recovery and PGM values.

The quantity of inert/non-oxidising gas added to the slurry depends on a number of factors but is preferably between the range of 0.1 and 10 m 3 /t of mineral bearing ore.

In one embodiment of the present inventive process, the slurry is conditioned with an inert/non-oxidising gas to achieve a very low dissolved oxygen level preferably below 15 ppm and most preferably below 0.1 ppm.

Figure 2 shows an alterative embodiment of the present invention. In this embodiment the inert/non-oxidising gas conditioning stage 40, which once again uses nitrogen, is placed prior to the reagent conditioning stage 30. Once again one or more of the activator 32, collector 34, frother 36 and depressant 38 may be added at the reagent conditioning stage The following examples serve to further clarify the present invention.

Two tests were conducted in which 1 kg charges of crushed ore containing disseminated nickel and copper sulphides with associated PGM minerals assaying 0.6% nickel and 0.2% copper were slurried in water to obtain pulp density 60 wt solids and -8milled in a stainless steel rod mill employing stainless steel rods to achieve P78 of approximately 75 microns.

The milled slurry was then transferred to a 2.5 litre Denver flotation cell and diluted with water to achieve a pulp density 35 wt solids. The agitator speed was set at 1200 rpm and maintained constant throughout the tests. The appropriate quantity of sulphide mineral collectors were added and the slurry was conditioned for 13 minutes. In the subject test sample (Example 1) N 2 gas at 1 litre per minute was added by injection into the S•slurry for the full 13 minutes of the collector conditioning. In the comparative test 0 0. (Example 2) no N 2 gas was added to the control sample. At the completion of collector i0.00. 10 conditioning an appropriate quantity of talcose depressant was added together with a quantity of frother. The slurry was conditioned for a further 2 minutes prior to flotation.

Flotation with air was commenced and six rougher concentrates were produced after 1, 2, 4, 8, 12 and 16 minutes respectively of flotation. Additional talcose depressant rd was added after production of the 1 st and 3 d rougher concentrates respectively.

S 15 The flotation products were assayed for nickel and copper content. The recovery of S"PGM minerals is known to be proportional to the flotation recovery of nickel and copper.

EXAMPLE 1 Metallurgical results of the test following the procedure outlined above with N 2 gas being added at 1 litre per minute for 13 minutes during collector conditioning. During this time the measured dissolved content of the slurry was close to zero: Flotation Performance sibti~ Product Ni) Ou"h~ Conc 1 7.76 15.5 8.3 49.7 Conc 1 +2 11.6 8.37 36.3 78.2 Conc 1 2 3 10.48 4.78 64.1 87.3 ConclI+ 2 3+4 9.12 4.02 68.0 89.5 Concl+2 3+ 4 +5 7.82 3.39 69.9 90.6 Concl+ 2+ 3+ 4+ 5±+6 6.67 2.88 71.0 9.

5 EXAMPLE 2 Metallurgical results of the comparative example with no inert gas conditioning following the procedure described above are as follows: Flotation Performance ~Ni'it C Ni Coc17.83 9.59 18.4 73.1 Concl1+2 8.61 7.08 30.1 80.5 Conc 1+ 2 +3 7.82 4.66 43.2 83.7 Conc I+ 2+ 3 +4 6.90 3.79 47.9 85.5 Conc I+ 2+ 3 +4 +5 5.71 2.96 51.5 86.6 Concl+ 2 +3 +4 +5 +6 4.73 2.38 53.5 187.4 In both examples, the flotation gas used was air.

The test data clearly indicates that conditioning with nitrogen gas has significantly increased the flotation recoveries of nickel and copper and the concentrate of the nickel and copper content.

The beneficial effect found from conditioning with nitrogen is quite surprising particularly as the example uses air as the flotation gas. Such an arrangement is much simpler to apply in practice than total nitrogen flotation or milling in the complete absence of oxygen.

The benefit of nitrogen conditioning was less pronounced on milled ore slurries S-already deficient in dissolved oxygen. In the examples given, the milled slurry after i' 10 transfer to the flotation cell had a dissolved oxygen content of approximately 60% of air saturation. In the test involving nitrogen conditioning, this was reduced to close to 0%.

0* S.The optimum for nitrogen conditioning time would depend upon a number of factors including ore types. Conditioning times with the inert gas may range from a few minutes up to several hours.

The present inventive process provides improved base metal sulphide and PGM recovery. It also improves the base metal grades of concentrate which, as will be clear to persons skilled in the art, has a significant impact on smelting of the resultant concentrate.

The present inventive inert/non-oxidising gas conditioning step may be accompanied by flotation using air, nitrogen, another inert gas or even oxygen depleted air. The flotation stages maybe arranged to selectively remove the various PGM varying base metal sulphides or alternatively the flotation stages maybe arranged to remove two or more PGM bearing base metal sulphides in a single flotation circuit.

It will also be clear to persons skilled in the art that the present invention provides an opportunity to simplify existing technology for the recovery of the PGMs.

-11- It will be understood that the present invention maybe embodied in forms other than that disclosed in the specification without departing from the spirit or scope of the invention.

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Claims (8)

12- THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:- 1. A process for the recovery of valuable sulphide mineral ores comprising providing a slurry of said ore, conditioning said slurry with suitable activators, collectors, frothers and/or depressants and subjecting the conditioned slurry to further conditioning with an inert/non-oxidising gas in a quantity conducive to improving separation of the sulphide minerals from the remainder of said ore, and subsequently subjecting said slurry to a final flotation treatment with a gas having a higher oxygen content than said inert/non-oxidising gas. 2. A process as claimed in claim 1 wherein the ore contains platinum group metal bearing minerals, said slurry being conditioned with the inert/non-oxidising gas in a quantity conducive to improving separation of the platinum group metal bearing minerals from the remainder of said ore. 3. A process as claimed in claim 1 wherein the ore contains base metal sulphides •selected from the group consisting of chalcocite, chalcopyrite, pentlandite, pyrrhotite and pyrite, said slurry being conditioned with an inert/non-oxidising gas in a quantity *conducive to improving separation of one or more of said base metal sulphides from the remainder of said ore. 4. A process as claimed in any one of claims 1 to 3 wherein the inertiion-oxidising gas is selected from the group consisting of nitrogen, argon, neon and mixtures thereof. 5. A process as claimed in any one of claims 1 to 3 wherein the inert/non-oxidising gas is selected from the group consisting of carbon dioxide, methane, propane, ethane and mixtures thereof. 6. A process as claimed in any one of the preceding claims wherein the final flotation treatment uses air or oxygen as the flotation gas.

13- 7. A process as claimed in any one of the preceding claims wherein the inert/non- oxidising gas is added to the slurry prior to the reagent conditioning stage. 8. A process as claimed in any one of the previous claims wherein nitrogen is added to the slurry after the reagent conditioning stage but prior to the final flotation treatment. 9. A process as claimed in any one of the preceding claims wherein the slurry is conditioned with an inert/non-oxidising gas for between 1 and 30 minutes. A process as claimed in any one of the preceding claims wherein the slurry is conditioned with an inert/non-oxidising gas for between 2 and 10 minutes. 11. A process as claimed in any one of the preceding claims wherein the slurry is 10 conditioned with an inert/non-oxidising gas to achieve a dissolved oxygen level below ppm. 12. A process as claimed in any one of the preceding claims wherein the slurry is conditioned with an inert/non-oxidising gas to achieve a dissolved oxygen level below 0.1 ppm. 13. A process as claimed in any one of the preceding claims wherein between 0.1 and *o i 10m of inert/non-oxidising gas is added to the slurry per tonne of mineral-bearing ore.

14. A process as claimed in any one of the preceding claims wherein the flotation treatment is conducted over several stages to selectively remove chalcopyrite, pentlandite, pyrrhotite, pyrite or other selected sulphide minerals.

15. A process as claimed in any one of the preceding claims wherein PGM bearing chalcopyrite is recovered followed by PGM bearing pentlandite followed by PGM bearing pyrrhotite and pyrite. -14-

16. A process as claimed in any one of the preceding claims wherein an initial step is conducted using the inert/non-oxidising gas as a flotation gas, prior to said final flotation treatment.

17. A process as claimed in claim 16 wherein the conditioning and an initial flotation step with the inert/non-oxidising gas are conducted simultaneously and prior to said final flotation treatment.

18. A process as claimed in claim 16 wherein after conditioning with the inert/non- oxidising gas, the slurry is transferred to a series of flotation cells, a first group of the cells using the inert/non-oxidising gas as a flotation gas and the remainder of the cells using a 10 gas having a higher oxygen content than said inert/non-oxidising gas as the flotation gas.

19. A process as claimed in claim 16 or claim 17 wherein the conditioning and flotation with the inert/non-oxidising gas is conducted in a milling circuit whereby the slurry leaves the milling circuit and is conditioned and floated using the inert/non-oxidising gas as the flotation gas, the tailings from this flotation step being returned to the mill for further 15 grinding and the subsequent final flotation treatment. A process for the treatment of platinum group metal bearing mineral ores substantially as hereinbefore described with reference to any one of the drawings and examples but excluding comparative examples. DATED this 10th Day of July, 1998 BOC GASES AUSTRALIA LIMITED Attorney: PAUL G. HARRISON Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS