AU2002248965B2 - Process for sulphide concentration - Google Patents

Description

WO 02/083316 PCT/AU02/00471 1 PROCESS FOR SULPHIDE CONCENTRATION FIELD OF THE INVENTION The present invention relates generally to a method and an apparatus for separating a solid contaminant from a valuable mineral concentrate. The invention relates particularly, though not exclusively, to gravity separation of magnesia minerals from a nickel sulphide concentrate such as a serpentinitic hosted low grade nickel sulphide ore.

BACKGROUND OF THE INVENTION The conventional development of low grade nickel sulphide serpentinitic ore bodies such as Mt Keith, Western Australia, have been limited by the requirement to produce a nickel concentrate product containing low levels of Magnesia (MgO) minerals. This constraint is usually referred to as the Iron to Magnesia ratio of the concentrate (Fe:MgO ratio). The MgO constraint is a result of a physical limitation of the downstream smelting process. The concentrate smelting process typically require Fe:MgO ratios of about 5.5, which corresponds to an MgO content of One means of increasing the Fe:MgO ratio is the addition of Fe to the concentrate however this is not an ideal solution as it dilutes the nickel content and reduces the smelter capacity. Hence the objective is to achieve an Fe:MgO ratio of 5.5 by rejecting MgO.

The conventional processing route for these types of ores involves crushing and grinding followed by concentration of the nickel through multiple stages of flotation.

Conditions in the flotation process are optimised to recover Ni minerals and reject MgO minerals. This technology has been applied at Mt Keith and the concentrate Fe:MgO has averaged around 2.9 that corresponds to a MgO content of about 10%. Although not 2 C meeting the acceptable Fe: MgO specification, it has been Spossible for the smelter to accept this concentrate through blending the Mt Keith concentrate with C- concentrates from other locations. This blending has provided the smelter with the required 5.5 Fe: MgO ratio.

V) However, the smelting requirement of the Fe: MgO of limits the future amount of Mt Keith concentrate that can Sbe smelted without blending with other concentrates.

0 10 SUMMARY OF THE INVENTION CI According to the present invention there is provided a method of processing a mineral stream containing valuable nickel sulphide and a solid contaminant in the form of magnesia (MgO) that includes the steps of: separating a feed stream in a first stage on a screen into a coarse stream of particles greater than 110 microns and a fines stream of particles less than 110 microns; separating the fines stream in a cyclone in a second stage and producing an ultra fines/slimes stream of P80 less than 25 microns and a middlings stream of greater than 25 microns; subjecting the middlings stream to flotation and recovering nickel sulphide which is sent to final concentrate and rejecting or depressing MgO in a tails stream; and treating the rejected/depressed MgOcontaining tail stream by gravity separation and concentrating the MgO.

Preferably the gravity separation in step is conducted in at least two stages such as a rougher stage and a scavenger stage arranged in series.

Preferably the coarse stream from step is ground and then floated to reject more of the MgO.

N:\Melbourne\Case\Patent\41000-41999\P4177 .AU. ]\Specis\P41775.AU.1 N032 amendmenta.doc 25/07/07 -3 eC Preferably the middlings stream is treated with an alkali and/or depressant to enhance flotation of the nickel sulphide in step to the final concentrate and depress C- the MgO to thereafter undergo the gravity separation.

V Preferably the ultrafine/slimes stream is subjected to flotation in a further step to reject any of the MgO to Supgrade the concentration of nickel sulphide.

O 10 Preferably the ultrafine/slimes stream is treated with an C< acid and/or activator to enhance flotation of the nickel sulphide to a final concentrate and depress the MgO to a concentrated contaminant or tails stream.

Preferably the MgO is rejected to a concentrated contaminant or tails stream which is subjected to flotation in a further step to recover residual nickel sulphide from the mineral concentrate.

Preferably the concentrated contaminant or tails stream is ground to liberate at least some of the residual nickel sulphide prior to said flotation.

Preferably the fines stream from step is from 30 to 110 microns.

According to the present invention there is also provided an apparatus for processing a mineral stream containing valuable nickel sulphide and a solid contaminant in the form of magnesia (MgO) minerals, the apparatus comprising: size separation means including a screen for separating the mineral stream into a coarse stream and a fines stream, with the fines stream being predominant in MgO; and a cyclone for separating the fines stream into an ultra fines/slimes stream and a middlings stream, with the middlings stream being predominant in MgO; and N\Melbourne\Caaes\Patent\410OO-41999\P41775.AU.\SpeCia\P41775.AU.1 N032 amendments.doc 25/07/0 4 C gravity separation means for separating the Smiddlings stream and thus reject a majority of the MgO from the middlings stream.

Preferably the gravity separation means includes a V) centrifugal separator.

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SPreferably the centrifugal separator is similar to a C Kelsey jig.

CI Preferably the apparatus also comprises flotation means disposed between and arranged to operatively cooperate with the size separation means and the gravity separation means, the flotation means being designed to subject nickel sulphide concentrate or middlings streams to flotation to recover nickel sulphide and reject MgO which is fed to the gravity separation means.

Preferably the apparatus also comprises treatment means for treating the nickel sulphide concentrate or middlings streams with alkali and/or depressant to enhance flotation of the nickel sulphide to a final concentrate and depress MgO to the gravity separation means.

Preferably the apparatus also comprises another flotation means for floating an overflow of the cyclone or the ultrafines/slimes stream to recover nickel sulphide and reject MgO.

Preferably the apparatus also comprises treatment means for treating the overflow or ultrafines/slimes streams with acid and/or activator to enhance flotation of the nickel sulphide to a final concentrate and depress MgO to a concentrated contaminant or tails stream.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order to achieve a better understanding of the nature N:\Melborne\Case a\Paent\41000-41999\P41775.AU.1\SpeciS\P41775.AU.1 N032 amendments.doc 25/07/07 5 (4 of the present invention a preferred embodiment of a method and an apparatus for separating a solid contaminant from a valuable mineral concentrate will now be explained c- in some detail, by way of example only, with reference to the attached flowsheet of Figure 1 which shows one Vt embodiment of a gravity/flotation circuit.

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SThe flowsheet of the embodiment of the invention shown in C- Figure 1 is based on pilot plant testing at Mt Keith, O 10 Western Australia, over a limited range of low grade C- nickel sulphide serpentinitic ore. The minerals stream introduced to the gravity circuit of these examples are a flotation concentrate having a high concentration of nickel with the resultant higher than allowable MgO content. The flotation concentrate is in this example either a rougher concentrate or a cleaner concentrate. It is to be understood for the purposes of this example that nickel is the valuable mineral and MgO or magnesia minerals are the solid contaminants.

The mineral stream of Figure 1 undergoes a two stage size separation wherein: i) the screen of the first stage provides a coarse stream of particles greater than 110 microns and a fines stream of particles less than 110 microns; and ii) the fines stream of less than 110 microns is subjected to the second stage separation whereupon a cyclone provides an ultrafine/slimes stream of p80 less than about 25 microns and a middlings stream of greater than around 25 microns.

The ultrafine/slimes stream is subjected to flotation at a low pH which selectively rejects MgO. During flotation of the ultrafine/slimes stream, acid and/or activator are added to enhance the flotation of nickel whilst depressing magnesia. The flotation concentrate is sent to final concentrate without further upgrading and the flotation tails is sent to a concentrated contaminant or tails N \Melbourne\Cases\Patent\41000-41999\P41775.AU.1\Speci\P41775.AU.1 N032 amendments.doc 25/07/07 6 stream. This flotation and upgrading of the ultrafine/slimes stream is typically performed at a pH of about 2 to The coarse stream of greater than 110 microns is reground V in a tower mill in order to liberate the nickel sulphide

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from the MgO. The liberated coarse stream is then floated Sin order to recover residual nickel sulphide and reject c MgO minerals to enhance the grade of the final O 10 concentrate. This also reduces the all important MgO C1 concentration in the final concentrate.

The middlings stream of a p80 of less than about microns is subjected to flotation to recover nickel sulphide which is sent to final concentrate, and reject or depress magnesia which undergoes gravity separation to concentrate the MgO. During flotation of the middlings stream, alkali and/or depressant are added to enhance the flotation of nickel sulphide whilst depressing MgO. In one example the pH of the middling stream is adjusted to a pH of between 9 to 11 using soda ash and the depressant guargum is added at rates of from 0 to 5000g/tonne flotation feed.

It was discovered that a large proportion of the MgO minerals in the Mt Keith concentrate are contained in the to 100 micron size fraction and that they are well liberated making physical separation possible.

Furthermore, the nickel sulphide minerals and magnesium minerals have a significantly different specific gravity which can be exploited using gravity separation equipment to achieve magnesia rejection.

In this embodiment the concentrated MgO tails of the middlings flotation circuit is fed to a single or multiple stage gravity separation. The concentrate from the gravity N;\Melbourne\Caes\Patent\4100-41999\P41775.AU.1\Specia\P41775AU.1 N032 amendments.doc 25/07/07 7 Sseparation device has relatively low concentrations of MgO and thus a very high Fe: MgO ratio. The tails from the gravity separation device reports together with the coarse Ce stream to the regrind tower mill.

V The preferred gravity separation device is a centrifugal

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separator designed so that both gravity and centrifugal Sforces are used to effect the required separation. The c Kelsey jig is such an example of the centrifugal separator O 10 and is particularly effective in separating the MgO C< minerals from the nickel sulphide minerals of the attached flowsheets.

The jig tails of both embodiments are sent to the tower mill together with the coarse material from the screen.

The tails are thus ground and floated together with the coarse material greater than 110 micron material with a view to rejecting more MgO in the flotation circuit to improve the grade of the final concentrate. The grind and float of the jig tails recovers additional nickel which may be otherwise lost and thus increases the recovery of the gravity circuit. That is, the combined gravity circuit flowsheet achieves high MgO rejection with minimal Nickel losses. In this embodiment this is effected by the combination of flotation, size separation, gravity separation and grinding to selectively reject MgO minerals while maintaining a high nickel recovery.

The application of a gravity separation device in this example poses a challenging task for traditional equipment due to the relatively fine particle size being treated.

Traditional gravity separation devices generally have a lower limit of around 100 microns and thus are not particularly well suited to nickel sulphide serpentinitic ores such as that which exists at Mt Keith, Western N:\Melbourne\Caes\Patent\41000-41999\P41775.AU. \Specio\P41775.AV.1 N032 amendments.doc 25/07/07 8 Australia. In the gravity circuit described, the Kelsey jig which uses centrifugal forces rather than gravity alone is effective in separating particles of a finer Ce particle size range. It is understood that the conventional use of gravity devices is to concentrate a l valuable mineral, for example in the mineral sands and tin Sindustry, as opposed to rejecting a contaminant such as Sits preferred application in the present invention. It is c also understood that centrifugal separators, such as the O 10 Kelsey jig, have not been used in the sulphide metal Cl industry.

The following table includes typical results from the pilot gravity/flotation circuit plant of Figure 1.

Stream Ni Grade MgO Grade Fe Grade Feed 20 8.6 26.1 Screen O/S 16.1 10.3 26.1 Cyclone O/F 18.1 9.5 23.5 Cyclone U/F 21 8.3 26.8 Float Jig Con 25.1 3.0 29.8 Jig Tail 8.6 24.2 17.7 Refloat Tail 4.1 29.7 19.4 Combined Con 22.9 5 27.2 This process increases the concentrate Fe: MgO ratio from about 3 to about 5.5. Thus, the process of this example has the potential to reject MgO from the Mt Keith concentrate achieving an Fe: MgO of 5.5 thereby making the final concentrate smeltable in its own right.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

For example, the gravity separator is not limited to a centrifugal separator but rather will be dictated by the N:\Mebourne\Case\Patent\41000-41999\P4177.AU.1\Specis\P41775.AU.1 N032 amendments.doc 25/07/07 9 particular mineral size and specific gravity of the solid contaminant to be rejected. The process need not be limited to a size separation but rather may involve C- gravity separation alone of an already liberated mineral concentrate/solid contaminant.

All such variations and modifications are to be considered Swithin the scope of the present invention the nature of which is to be determined from the foregoing description.

C C- It is to be understood that, if any reference to prior art is made herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country.

N:\Melbourne\Cases\Patent\41000-41999\P41775.AU.1\Specil\P41775.AU.l N032 amendments.doc 25/07/07

Claims (16)

1. A method of processing a mineral stream CI containing valuable nickel sulphide and a solid contaminant in the form of magnesia (MgO) that includes V) the steps of: 11D 00 0 separating a feed stream in a first stage C on a screen into a coarse stream of particles greater than 0 10 110 microns and a fines stream of particles less than 110 CI microns; separating the fines stream in a cyclone in a second stage and producing an ultra fines/slimes stream of P80 less than 25 microns and a middlings stream of greater than 25 microns; subjecting the middlings stream to flotation and recovering nickel sulphide which is sent to final concentrate and rejecting or depressing MgO in a tails stream; and treating the rejected/depressed MgO- containing tail stream by gravity separation and concentrating the MgO.

2. A method as defined in claim 1 wherein the gravity separation in step is conducted in at least two stages such as a rougher stage and a scavenger stage arranged in series.

3. A method as defined in claim 1 or claim 2 wherein the coarse stream from step is ground and then floated to reject more of the MgO.

4. A method as defined in any one of the preceding claims wherein the middlings stream is treated with an N,\Melbourne\Cases\Patent\41OOO-41999\P41775.AU.1\Specis\P4177 .AU.1 N032 amendmente.doc 25/07/07 11 Salkali and/or depressant to enhance flotation of the nickel sulphide in step to the final concentrate and depress the MgO to thereafter undergo the gravity CI separation. V)

5. A method as defined in any one of the preceding \O claims wherein the ultrafine/slimes stream is subjected to 00 Sflotation in a further step to reject any of the MgO to c upgrade the concentration of nickel sulphide. CI

6. A method as defined in claim 5 wherein said ultrafine/slimes stream is treated with an acid and/or activator to enhance flotation of the nickel sulphide to a final concentrate and depress the MgO to a concentrated contaminant or tails stream.

7. A method as defined in any one of the preceding claims wherein the MgO is rejected to a concentrated contaminant or tails stream which is subjected to flotation in a further step to recover residual nickel sulphide from the mineral concentrate.

8. A method as defined in claim 7 wherein the concentrated contaminant or tails stream is ground to liberate at least some of the residual nickel sulphide prior to said flotation.

9. A method as defined in any one of the preceding claims wherein the fines stream from step is from to 110 microns.

An apparatus for processing a mineral stream containing valuable nickel sulphide and a solid contaminant in the form of magnesia (MgO) minerals, said apparatus comprising: size separation means including a screen for separating the mineral stream into a coarse stream and a N:\Melbourne\Caes\Patent\41000-41999\P41775 .AU.JSpecis\P41775.AU.1 N032 amendmenta.doc 25/07/07 12 Sfines stream, with the fines stream being predominant in MgO, and a cyclone for separating the fines stream into an pC ultra fines/slimes stream and a middlings stream, with the middlings stream being predominant in MgO; and In gravity separation means for separating the Smiddlings stream and thus reject a majority of the MgO 00 from the middlings stream. 0 10

11. An apparatus as defined in claim 10 wherein said C- gravity separation means includes a centrifugal separator.

12. An apparatus as defined in claim 11 wherein the centrifugal separator is similar to a Kelsey jig.

13. An apparatus as defined in any one of claims to 12 also comprising flotation means disposed between and arranged to operatively cooperate with the size separation means and the gravity separation means, said flotation means being designed to subject nickel sulphide concentrate or middlings streams to flotation to recover nickel sulphide and reject MgO which is fed to the gravity separation means.

14. An apparatus as defined in claim 13 further comprising treatment means for treating the nickel sulphide concentrate or middlings streams with alkali and/or depressant to enhance flotation of the nickel sulphide to a final concentrate and depress MgO to the gravity separation means.

An apparatus as defined in any one of claims to 14 also comprising another flotation means for floating an overflow of the cyclone or the ultrafines/slimes stream to recover nickel sulphide and reject MgO.

16. An apparatus as defined in claim 15 further N:\Melbourne\Cases\Patent\41000-41999\P41?75.AU.1\Specis\P41775.AU.1 N032 amendnentgedoc 25/07/07 13 comprising treatment means for treating the overflow or ultrafines/slimes streams with acid and/or activator to enhance flotation of the nickel sulphide to a final V) concentrate and depress MgO to a concentrated contaminant or tails stream. 00 N:\Melbourne\Cae\Patent\41OO.41999\P41775 AU. 1\SpeCis\P4177S.AU.1 N032 amendmentB.doc 25/07/07