AU720049B2

AU720049B2 - Pretreatment of a sulphide mineral pulp

Info

Publication number: AU720049B2
Application number: AU43696/97A
Authority: AU
Inventors: Ian Clark; James McQuie; John Ralston
Original assignee: WMC Resources Ltd
Current assignee: BHP SSM Indonesia Holdings Pty Ltd
Priority date: 1996-11-11
Filing date: 1997-11-03
Publication date: 2000-05-25
Anticipated expiration: 2017-11-03
Also published as: AU4369697A

Description

EDITORIAL NOTE APPLICATION NUMBER- 43696/97 THIS SPECIFICATION DOES NOT CONTAIN A PAGE 1 2 PRETREATMENT OF A SULPHIDE MINERAL PULP FIELD OF THE INVENTION The present invention relates generally to a process for the improved flotation of nickel sulphide ores.

BACKGROUND TO THE INVENTION A. conventional flotation technique for separating valuable nickel bearing sulphide minerals from a nickel sulphide ore generally involves the following steps: i) milling of the nickel sulphide ore and slurrying of the milled ore with water to form an aqueous pulp, this step being known as beneficiation; ii) adding collector and depressant agents to the aqueous pulp; and iii) flotation of the aqueous pulp in one or more .15 stages wherein the separation of sulphide and MgO bearing gangue minerals from the pulp as concentrate and tailings, respectively, is effected.

The efficiency of flotation of sulphide minerals in step iii) is controlled by a number of variables, one of which is the particle size and configuration of the mineral being floated. In general, the greater the quantity of slime bearing constituents, the poorer the separation of minerals in gangue. In most primary nickel sulphide deposits, the naturally occurring slimes and those produced by beneficiation are of sufficient quantity to detrimentally affect overall flotation recoveries.

Attempts to avoid slime formation have included efforts to eliminate fine grinding of an ore. As an example, some mill feeds are ground to approximately 80% passing 125 microns. Such a grind is necessary for optimum liberation of the desired minerals from the ore. If the ore is not ground fine enough, slime formation may be avoided, but the recovery of the desired mineral is low. Another technique 3 is to physically separate the slimes fraction by such techniques as hydrocyclone separation at fine sizes. The slimes fraction can then be treated separately, possibly under different condition than the deslimed material, to effect the desired separation.

Addition of chemicals to suppress the detrimental effect of slimes has been tried with limited success. The chemicals have been found not to sufficiently improve the grade of rougher concentrates so as to permit a more efficient cleaner flotation circuit.

SUMMARY OF THE INVENTION An intention of the present invention is to provide a **process for the improved flotation of nickel sulphide ores whereby the selectivity between valuable nickel bearing sulphide minerals and slimes of MgO bearing gangue minerals is improved and the recovery of the valuable nickel bearing sulphide minerals is substantially optimised.

eoto According to one aspect of the present invention there is provided a pretreatment process for the improved flotation of valuable nickel bearing sulphide minerals contained in an aqueous pulp of a nickel sulphide ore, the pretreatment process comprising the step of: adding a polyethylene oxide/polypropylene oxide block copolymer to the aqueous pulp in preparation for flotation of the valuable nickel bearing sulphide minerals from said pulp, said block copolymer being effective in dispersing slimes of MgO bearing gangue minerals contained in the aqueous pulp whereby the valuable nickel bearing sulphide minerals and the slimes of MgO bearing gangue minerals can, during flotation, be separated with improved selectivity and the recovery of the valuable nickel bearing sulphide minerals is substantially optimised.

4 According to another aspect of the present invention there is provided a process for the improved flotation of valuable nickel bearing sulphide minerals contained in an aqueous pulp of a nickel sulphide ore, said process comprising the steps of: adding a polyethylene oxide/polypropylene oxide block copolymer to the aqueous pulp, said block copolymer being effective in dispersing slimes of MgO bearing gangue minerals contained in the aqueous pulp; and floating the valuable nickel bearing sulphide minerals and depressing or at least suspending the slimes of MgO bearing gangue minerals whereby the valuable nickel bearing sulphide minerals and the slimes of MgO bearing gangue minerals are separated with improved selectivity and the recovery of the valuable nickel bearing sulphide minerals is substantially optimised.

Typically, the addition of said block copolymer in step (a) o can be performed either prior to or during flotation.

Preferably, the addition of the polyethylene oxide/polypropylene oxide block copolymer at step (a) occurs prior to flotation of the valuable nickel bearing sulphide minerals. Typically, said block copolymer is added to the aqueous pulp. Alternatively, the block S. copolymer is added to water, the water together with the block copolymer then being slurried with the nickel sulphide ore to form the aqueous pulp.

Typically, the addition of the block copolymer to the aqueous pulp in step occurs at its natural pH of between approximately pH 7 to 8. However, acid or base may also be added to the aqueous pulp so as to float the sulphide minerals in the pH range of between approximately pH 2 to 5 Preferably, the polyethylene oxide/polypropylene oxide block copolymer is added to the aqueous pulp at step in an amount of at least approximately 2 parts of said copolymer per million parts of the aqueous pulp, by weight.

Typically, the block copolymer is added to the aqueous pulp at step in an amount of between approximately 2 to 200 parts of said copolymer per million parts of the aqueous pulp, by weight. More typically, the block copolymer is added in an amount of between approximately 2 to 50 parts of said copolymer per million parts of the aqueous pulp, by weight.

Typically, the polyethylene oxide/polypropylene oxide block copolymer consists of a nonionic tri-block copolymer of the structure polyethylene oxide/polypropylene oxide/ polyethylene oxide.

More typically, the tri-block copolymer has a structure represented by the general formula:

H-(OCH

2

CH

2 )a (OCH(CH,)CH 2 )b (OCH 2

CH

2 )a OH This structure allows independent manipulation of both the 20 overall molecular weight of the block copolymer and the relative proportion of ethylene oxide and propylene oxide in said copolymer.

Typically, the block copolymer contains between approximately 20 to 80% by weight ethylene oxide, the balance being propylene oxide. Typically, the block copolymer has an overall molecular weight of at least 4000 grams/mole.

Typically, the step of floating the valuable nickel bearing sulphide minerals at step is performed during a rougher flotation stage. Alternatively, the step of floating the 6 valuable nickel bearing sulphide minerals is performed during a cleaner or a recleaner flotation stage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In order that the invention be more clearly understood, several examples of the process for the improved flotation of nickel sulphide ores will now be described in some detail, by way of example only.

The details of rougher and cleaner flotation are well known to those skilled in the art. Conventional procedures and apparatus used for rougher and cleaner flotation can be used in conjunction with the various examples of the present invention. Consequently, these conventional procedures and apparatuses will not be described in any detail herein.

In the examples described, the nickel sulphide ore was obtained from Mt Keith, Western Australia, and contained pentlandite, millerite, heazlewoodite, chalcopyrite, pyrrhotite, pyrite and magnesium oxide containing gangue minerals including serpentine. The nickel sulphide ore was prepared for flotation concentration in the usual manner.

That is, the ore is ground such that 80% of the material is 125 microns or finer, and the ground ore was then slurried with water to form an aqueous flotation pulp. The particle size of the ground ore can vary widely this being dependent upon the ore to be floated. It is also common commercial practice to blend batches of ore of various particle sizes.

Furthermore, the concentration of ore solids in the aqueous flotation pulp can differ widely. The particle size or size range of the ore feed used to form the flotation pulp, and the concentration of solids in the flotation pulp are generally chosen so as to give the optimum flotation concentration for the ore being treated.

7 In the following examples of the present invention a nonionic polyethylene oxide/polypropylene oxide (PEO/PPO) block copolymer was added to the aqueous flotation pulp prior to flotation. It should be appreciated that the block copolymer can be added to water which is used to form the flotation pulp or, alternatively, may be added directly to the aqueous pulp once it is formed.

The block copolymer was added in an amount sufficient to increase recovery of the desired valuable nickel bearing sulphide minerals. Ordinarily, this can be accomplished with the addition of as little as approximately 2 parts of block copolymer per million parts (ppm) of aqueous flotation pulp, by weight. With sulphidic ores having very high levels of naturally occurring slimes or with difficult if* 15 to float ores, it may be necessary to use at least 20 ppm of the block copolymer. If desired, levels of PEO/PPO copolymer up to 200 ppm can be added, although this would not usually be necessary. Levels of PEO/PPO copolymer in excess of about 200 ppm can have an adverse effect on the 20 rougher and cleaner concentrates. Therefore, from between approximately 2 to 20 ppm of a PEO/PPO copolymer is preferred.

The PEO/PPO copolymers used in the following examples were viscous liquids, waxes, or solids. The PEO/PPO copolymers 25 comprise block copolymers of ethylene oxide and propylene oxide copolymers which are soluble in water, alcohol, and other polar solvents. The distinguishing feature of these block copolymers is the tri-block structure, as represented by the general formula: H- (OCH 2

CH

2 )a (0-CH(CH 3

)-CH

2 )b (OCH 2

CH

2 )a-OH This structure allows independent manipulation of both the overall molecular weight and the proportion of the 8 ethylene-oxide component and the propylene-oxide component in the copolymer.

Examples of suitable PEO/PPO copolymers are the TERIC or SYNPERONIC range of copolymers supplied by ICI in Australia and the United Kingdom. In their pure form these copolymers are either liquids, waxes, or solid flake but commercial mixtures containing diluents such as water to butanol and salts, such as NaCl, can be supplied as viscous liquids. It has been found that the minor diluents do not have any significant effect on the copolymer and, thus, can be used as commercially available.

As to the desired copolymer composition, they should contain from between 30 to 80% by weight ethylene-oxide in the copolymer, with the balance being propylene oxide. The 15 copolymer preferably has an overall molecular weight of greater than approximately 4000 grams/mole. This copolymer composition is exemplified by P103 or F68 supplied by ICI.

The invention will now be further described with reference to the following examples.

20 EXAMPLE 1 *"*Tests were conducted on the flotation of a problematic low grade nickel sulphide ore from Mt. Keith, Western Australia, which was ground to 80% minus 125 microns. The minus 12 micron slimes were separated using a small hydrocyclone and the slimes were floated in the presence of the PEO/PPO copolymer (F68 or P103 supplied by ICI), and in the absence of a block copolymer. Table 1 indicates the results obtained using a rougher/cleaner/recleaner flowsheet typical for such ores.

9 TABLE 1 Flotation of Mt Keith Slimes with and without Block Copolymers No copolymer Recleaner concentrate Ni Assay 6.2% Ni Recleaner concentrate MgO Assay 18.5% MgO Recleaner Ni recovery 13.2% With 12 ppm F68 Recleaner concentrate Ni Assay 7.5% Ni Recleaner concentrate MgO Assay 17.4% MgO Recleaner Ni recovery 33.6% With 12 ppm P103 Recleaner concentrate Ni Assay 10.2% Ni Recleaner concentrate MgO Assay 15.4% MgO 15 Recleaner Ni recovery 40.8% It will be appreciated from the results of Table 1 that the S* addition of 12 ppm of the PEO/PPO block copolymer (either F68 or P103) results in a considerable improvement in the nickel recovery and concentrate nickel grade. The 20 beneficial effect the PEO/PPO copolymer provides in the control of MgO bearing gangue slimes was evident from the reduction in concentrate MgO grade from such ores.

EXAMPLE 2 A basic nickel sulphide ore containing about 0.6% nickel 25 and about 1.2% sulphur was wet ground in the presence of a conventional amount of ethyl xanthate. The wet ground feed was subject to a 4 minute rougher flotation stage. The rougher concentrate produced was further treated in a minute cleaner and a 2.5 minute recleaner stage. The rougher tail was subjected to a scavenger flotation stage as is typical for such processes. Conventional additions of frother and ethyl xanthate were also made prior to cleaning and scavenging. The results of this test without a PEO/PPO copolymer are reported in Table 2. A comparative test was performed with the addition of 0.1 g of the ICI 10 PEO/PPO copolymer F68 per kilogram of ore. This addition was made prior to the rougher flotation stage. The comparative results are also set forth in Table 2.

TABLE 2 Effect of PEO/PPO Copolymer on Recleaner Recovery Grades Without F68 Recleaner concentrate Ni Assay 19.9% Ni Recleaner concentrate S Assay 31.3% S Recleaner Ni recovery 50.3% Combined Tail Ni Assay 0.29% Ni With 0.1 g F68 Recleaner concentrate Ni Assay 18.9% Ni Recleaner concentrate S Assay 29.6% S Recleaner Ni recovery 60.8% Combined Tail Ni Assay 0.23% Ni *The composition of the recleaner concentrate and the combined tailings (scavenger and cleaner tailings) clearly shows the effectiveness of the ICI PEO/PPO copolymer F68.

The recleaner test with the PEO/PPO copolymer produced a 20 slightly lower grade of concentrate with an increased recovery in the cleaner resulting in a 10.5% higher nickel recovery in the final concentrate.

It should be noted that the usual flotation reagents (such as collectors, frothers, depressing agents, activating agents, and the like) added to the flotation pulps can be used in their usual amounts and for their usual effects.

The PEO/PPO copolymer has been observed not to interfere with the activity of these reagents.

Whilst the precise theory is not totally understood, it is believed the PEO/PPO block copolymer functions by dispersion of the MgO bearing gangue slimes which are particularly deleterious to sulphide flotation, and in particular nickel sulphide flotation. As will be appreciated from the preceding examples, the addition of a 11 PEO/PPO copolymer greatly and unexpectedly improves flotation by improving the efficiency of separation between the valuable sulphide minerals and gangue slimes resulting in higher recoveries of the desired nickel minerals in the final concentrate and improved concentrate grades.

The process for the improved flotation of nickel bearing sulphide minerals described above has a number of significant advantages over conventional flotation techniques including: the separation between valuable sulphide minerals and slimes of MgO bearing gangue minerals is improved thus increasing the grade of the flotation concentrate; (ii) the recovery of valuable nickel bearing sulphide minerals is substantially optimised without significantly lowering the grade of the flotation concentrate; (iii) the collection of slimes of MgO bearing gangue minerals is minimised in the flotation concentrate thereby lowering the weight of said concentrate; and e 6a (iv) the improved process can be used in conjunction with conventional flotation techniques wherein known reagents are substantially unaffected by the addition of a PEO/PPO copolymer.

Now that several examples of the invention have been described in detail, it will be apparent to persons skilled 25 in the relevant arts that numerous variations and S"modifications can be made without departing from the basic inventive concepts. For example, a range of PEO/PPO block copolymers other than those specifically described may be appropriate for the process of the present invention.

Furthermore, the addition of the PEO/PPO block copolymer may be made either before or during flotation of the valuable nickel bearing sulphide minerals from an aqueous pulp which may have been preconditioned with either acid or base.

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

Furthermore, the preceding examples are provided to illustrate specific embodiments of the invention and not intended to limit the scope of the present invention.

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Claims

2. A process for the improved flotation of valuable nickel bearing sulphide minerals contained in an aqueous pulp of a nickel sulphide ore, said process comprising the steps of: 20 adding a polyethylene oxide/polypropylene oxide block copolymer to the aqueous pulp, said block copolymer being effective in dispersing slimes of MgO bearing gangue r o minerals contained in the aqueous pulp; and floating the valuable nickel bearing sulphide minerals and depressing or at least suspending the slimes of MgO bearing gangue minerals whereby the valuable nickel bearing sulphide minerals and the slimes of MgO bearing gangue minerals are separated with improved selectivity and the recovery of the valuable nickel bearing sulphide minerals is substantially optimised.
3. A process for the improved flotation of valuable nickel bearing sulphide minerals as defined in claim 2 wherein the addition of the polyethylene oxide/polypropylene oxide block copolymer at step (a) 14 occurs prior to flotation of the valuable nickel bearing sulphide minerals.
4. A process for the improved flotation of valuable nickel bearing sulphide minerals as defined in claim 3 wherein said block copolymer is added to the aqueous pulp. A process for the improved flotation of valuable nickel bearing sulphide minerals as defined in claim 4 wherein acid or base is added to the aqueous pulp so as to float the sulphide minerals in the pH range of between approximately pH 2 to
6. A process for the improved flotation of valuable nickel bearing sulphide minerals as defined in claim 4 ~wherein the addition of the block copolymer to the aqueous S pulp in step occurs at its natural pH of between approximately pH 7 to 8. S
7. A process for the improved flotation or a pretreatment process for the improved flotation of valuable nickel bearing sulphide minerals as defined in any one of Sthe preceding claims wherein the polyethylene 20 oxide/polypropylene oxide block copolymer is added to the r aqueous pulp at step in an amount of at least approximately 2 parts of said copolymer per million parts of the aqueous pulp, by weight.
8. A process for the improved flotation or a pretreatment process for the improved flotation of valuable nickel bearing sulphide minerals as defined in claim 7 wherein the block copolymer is added to the aqueous pulp at step in an amount of between approximately 2 to 200 parts of said copolymer per million parts of the aqueous pulp, by weight. 15
9. A process for the improved flotation or a pretreatment process for the improved flotation of valuable nickel bearing sulphide minerals as defined in claim 7 wherein the block copolymer is added in an amount of between approximately 2 to 50 parts of said copolymer per million parts of the aqueous pulp, by weight. A process for the improved flotation or a pretreatment process for the improved fldtation of valuable nickel bearing sulphide minerals as defined in any one of the preceding claims wherein the polyethylene oxide/polypropylene oxide block copolymer consists of a nonionic tri-block copolymer of the structure polyethylene oxide/polypropylene oxide/ polyethylene oxide.
11. A process for the improved flotation or a pretreatment process for the improved flotation of valuable nickel bearing sulphide minerals as defined in any one of the preceding claims wherein the block copolymer contains between approximately 20 to 80% by weight ethylene oxide, the balance being propylene oxide. see* '9-
12. A process for the improved flotation or a pretreatment process for the improved flotation of valuable 6 nickel bearing sulphide minerals as defined in any one of the preceding claims wherein the block copolymer has an overall molecular weight of at least 4000 grams/mole.
13. A process for the improved flotation or a pretreatment process for the improved flotation of valuable nickel bearing sulphide minerals substantially as herein described. Dated this 3rd day of November 1997. WMC RESOURCES LTD By Its Patent Attorneys: GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia