AU729901B2 - pH adjustment of an aqueous sulphide mineral pulp - Google Patents

Description

P/00/011 Regulation 3.2

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD

PATENT

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0**r Name of Applicant: Address of Applicant: Actual Inventor: Address for Service: WMC RESOURCES LIMITED 37TH FLOOR, QV1 BUILDING 250 ST. GEORGE'S TERRACE PERTH WA 6000 JAMES McQUIE and IAN CLARK Griffith Hack Co.

256 Adelaide Terrace (6 Floor) PERTH WA 6000 Standard Complete Specification for the invention entitled: pH ADJUSTMENT OF AN AQUEOUS SULPHIDE MINERAL PULP Details of Associated Provisional Applications: Australian Provisional Patent Application No. P00034 filed on 22 May 1996 The following is a full description of this invention, including the best method of performing it known to me:- 2 pH ADJUSTMENT OF AN AQUEOUS SULPHIDE MINERAL PULP FIELD OF THE INVENTION The present invention relates generally to a process for the improved flotation of sulphide minerals and relates particularly, though not exclusively, to the improved flotation of serpentine-hosted nickel sulphide ores.

BACKGROUND TO THE INVENTION A conventional mineral processing technique for separating sulphide minerals from a nickel sulphide ore involves the following steps: crushing and milling of the nickel sulphide ore :i to form a pulp having minerals of a desired fineness, ii) adding collector and depressant agents to the pulp, 0 15 iii) adding acidic or alkaline solutions to the pulp, 0 .0 and iv) flotation of the pulp in one or more stages wherein the separation of sulphide and gangue minerals from the pulp as concentrate and tailings, respectively, is 20 effected.

Where flotation of the pulp is performed in multiple 000.

stages, the collector/depressant agents and the acidic or alkaline solutions are added prior to each stage of flotation. The addition of the collector agents to the pulp renders the sulphide minerals hydrophobic, and the addition of the depressant agents minimises the recovery of gangue minerals in the flotation concentrate. The addition of the acidic or alkaline solutions improves the effect of the collector and depressant agents.

The flotation concentrate including valuable sulphide minerals is then filtered in preparation for drying and/or smelting. For flash smelting reduced levels of gangue 3 minerals, in particular minerals, is desirable.

magnesium-containing gangue It is generally understood that sulphide pulps having relatively high alkalinity or pH values hinder flotation, resulting in the depression of sulphide minerals. It is also understood that most collector agents, especially xanthates, are chemically decomposed below a pH value of approximately 3. Accordingly, flotation is conventionally practised at pH values of between approximately 4 to 12.

SUMMARY OF THE INVENTION An intention of the present invention is to provide a process for the improved flotation of sulphide minerals, said process resulting in a reduced recovery of gangue minerals and an improved selectivity between gangue 15 minerals and valuable sulphide minerals in a flotation concentrate.

According to the present invention there is provided a process for the improved flotation of valuable sulphide minerals contained in a pulp, said process comprising the 20 steps of: adjustinq the DH of the n]n t1r an ff1e~, (b) relatively low pH value so as to improve the hydrophobicity of the valuable sulphide minerals; and floating the valuable sulphide minerals and depressing or at least suspending the gangue minerals in the pH adjusted pulp thereby separating said minerals with improved selectivity.

It has been observed that by adjusting the pH to the effective relatively low pH value there is achieved an increased rejection of gangue minerals and an improved recovery of the valuable sulphide minerals.

4 It is believed that, by adjusting the pH of the pulp to the effective relatively low pH value, the surface chemistry of the valuable sulphide minerals in the pulp is converted to elemental sulphur which is particularly hydrophobic. It is understood that the relatively acidic pulp acts to dissolve FeO which may coat the valuable sulphide mineral and thus inhibit its flotation.

Typically, process step involves adjusting the pH of the pulp to a value of between approximately 0.5 to Previously this relatively low pH value was considered inappropriate in so far as collector agents used in conventional flotation processes are only effective within a pH range of from between approximately 4 to 12.

Typically, process step involves conditioning the pulp 15 with an acidic solution for a predetermined period.

Generally, the predetermined period will be from between approximately 1 minute to 3 hours.

In one example, the acidic solution used to condition the pulp is sulphuric acid at an addition rate of between approximately 5 to 50 kg of sulphuric acid, per tonne of sulphide ore.

Typically, the process for the improved flotation of valuable sulphide minerals does not require addition of a collector agent to the pulp, said collector agent conventionally used to affect the hydrophobicity of sulphide minerals contained in a sulphide ore.

Accordingly, "collectorless flotation" can be performed at process step (b) In some instances the process for the improved flotation of valuable sulphide minerals further involves the addition of a depressant agent to the pulp, said depressant agent added in a reduced amount compared with conventional flotation 5 processes, so that during flotation in process step (b) depression of the gangue minerals is promoted thus minimising the recovery of gangue minerals in the concentrate. In one example, the depressant agent includes sodium carboxymethylcellulose (CMC) or a derivative thereof.

Typically, process step is performed subsequent to a conventional flotation stage so that adjustment of the pH of the pulp in process step involves adjustment of a flotation concentrate recovered from the conventional flotation stage. Advantageously, this reduces acid .consumption during process step acid consumption being a function of acid soluble gangue minerals, such as o serpentine, which are present in a sulphide ore.

15 Alternatively, process step is performed subsequent to milling of the sulphide ore. Typically, the improved flotation process involves at least two stages of flotation, namely a rougher and cleaner stage. However, .'.the number of flotation stages will depend on the nature of the ore and the downstream processing, such as smelting or further hydrometallurgical treatment, of the flotation concentrate.

The improved flotation process of the present invention is particularly well suited to a serpentine-hosted nickel sulphide ore containing pentlandite, millerite, heazlewoodite, chalcopyrite, pyrrhotite, pyrite and magnesium-containing gangue minerals including serpentine.

In this example, the valuable sulphide minerals include pentlandite and chalcopyrite and the magnesium-containing gangue minerals include brucite and serpentine.

BRIEF DESCRIPTION OF DRAWINGS In order to facilitate a better understanding of the invention several examples of a process for the improved flotation of sulphide minerals will now be described in 6 some detail, by way of example only, with reference to the following drawings in which: Figure 1 is a flowsheet illustrating pH adjustment subsequent to a rougher flotation stage; and Figure 2 is a flowsheet showing pH adjustment prior to flotation.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS As illustrated in the flowsheet shown in Figure i, a basic nickel sulphide ore (obtained from the Mt Keith region in Western Australia) containing 0.81% nickel, 0.9% sulphur, .and 40% MgO by weight is wet ground in the presence of a conventional amount of ethyl xanthate at a natural pH of approximately 9.0. The wet ground Mt Keith nickel sulphide ore or pulp together with a conventional amount of frother, S: 15 in this example H407, is then subjected to a four minute rougher flotation stage.

A rougher concentrate produced from the rougher flotation stage is then conditioned for approximately five minutes S" with an amount of sulphuric acid capable of reducing the pH 20 of the rougher concentrate to approximately pH Typically, the acid consumption is between approximately to 20 kilograms of sulphuric acid (98% w/w) per tonne of nickel sulphide ore feed. However, acid consumption with other ores may greatly exceed this value and the critical factor is not the quantity of acid consumed but rather the correct pH to which the pulp is adjusted.

The pH adjusted rougher concentrate is then fed to a cleaner flotation stage and subjected to reflotation to produce a cleaner concentrate. A flotation separation of the sulphide minerals (principally pentlandite with minor millerite, heazlewoodite, pyrrhotite and pyrite) from the MgO bearing gangue minerals (mainly serpentines, hydroxycarbonates and brucite) that have not already dissolved is 7 effected at this stage. The cleaner concentrate is then pH adjusted to maintain a pH value of less than approximately The pH adjusted cleaner concentrate is then refloated for a suitable time in a recleaner flotation stage to produce a recleaner or final concentrate. The alkaline rougher tailings from the rougher flotation stage are combined with the cleaner and recleaner tailings prior to disposal.

Thus, no alkali solution is required and the tailings mixture self-neutralises to pH7 within approximately minutes. The self-neutralisation of the tailings mixture is largely due to the reaction between acid and the MgO o gangue in the nickel sulphide ore.

The recleaner or final concentrate may not exhibit any 15 self-neutralisation capacity largely due to the lack of MgO bearing minerals in the final concentrate stream. Thus, the final concentrate may need to be neutralised prior to filtration and lime or caustic soda is generally used for this purpose. The final concentrate is then filtered in preparation for drying and/or further processing.

As conventionally practiced, the tailings are pumped to thickeners to effect a solid/liquid separation. Process water is recovered and the thickened tailings are deposited in tailings dams. The residence time in the thickeners is considered adequate for total neutralisation to occur.

Parallel tests comparing conventional flotation at natural pH, and flotation according to the preceding example of the present invention incorporating pH adjustment gave the following results.

8 TABLE 1 FLOTATION OF MT KEITH SULPHIDE MINERALS WITH pH ADJUSTMENT OF A ROUGHER CONCENTRATE Recleaner or Final Recovery Cleaner Test Concentrate Tailings %Ni i 0MgO Wt% Ni% Conventional 26.9 5.9 1.7 60.2 .81 pH adjusted 30.5 4.0 1.8 63.2 .33 It will be appreciated from the results of Table 1 that an increased recovery of nickel and a reduced recovery of MgO 10 is achieved in the final concentrate where the pulp has been pH adjusted. Furthermore, a reduced percentage of nickel is lost in the cleaner tailings and thus pH adjustment of the pulp shows an improved selectivity between valuable and gangue bearing minerals.

15 In another example of the present invention as illustrated in Figure 2, the ground Mt Keith ore or pulp is pH adjusted prior to the rougher flotation stage. That is, approximately 47 kg of sulphuric acid per tonne of ore is added to the pulp, and the pulp conditioned for approximately 5 minutes to achieve a pH of approximately so as to maximise the effects achieved during flotation. It will be appreciated that the period of acid conditioning will depend largely on the quantity of acid soluble minerals within the pulp.

Parallel tests on the Mt Keith ore comparing conventional flotation at natural pH and acid conditioning or pH adjustment prior to rougher flotation gave the following results.

9 TABLE 2 FLOTATION OF MT KEITH SULPHIDE MINERALS WITH pH ADJUSTMENT PRIOR TO ROUGHER FLOTATION Test Rougher Concentrate Grade Recovery %Ni MgO N i Conventional 28.9 8.4 41.2 pH adjusted 31.1 6.2 49.6 *9 *5

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It will be appreciated from the results of Table 2 that an increased recovery of nickel was achieved in the flotation concentrate where the Mt Keith pulp has been pH adjusted prior to rougher flotation. An increase in nickel and a decrease in the MgO Grade is also clearly shown with pH adjustment.

As further illustrated in the flowsheet of Figure 2, the rougher concentrate may require pH adjustment prior to the 15 cleaner and recleaner flotation stages. The recleaner or final concentrate and the recleaner or scavenger tailings are processed conventionally as described in the preceding example.

Another ore sample consisting of a blend of 20 Perseverance Underground and 25% Rocky's Reward (being Western Australian ore bodies located in the Leinster/ Mt Keith region) is wet ground to form a Western Australian pulp blend.

The Western Australian pulp blend is then floated conventionally in a rougher and a cleaner flotation stage at a natural pH without acid conditioning. The results of this standard test without pH adjustment are presented in Table 3. Cleaner flotation realised a nickel recovery of approximately 82.3% at a Grade of approximately 10% nickel and 6.95% MgO.

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0 0 00 10 TABLE 3 FLOTATION OF A WESTERN AUSTRALIAN SULPHIDE MINERAL BLEND WITH pH ADJUSTMENT OF A ROUGHER CONCENTRATE Cleaner Total Recovery to Cleaner Dissoin Conc Grade Cleaner Concentrate Tail Ni(% Test pH Leach M% Grade Nie i MgO Ni MgO Fe Mass %)Ni MgO Conventional Natural 10.0 6.95 82.3 4.7 35.3 15.5 0.83 pH Adjusted 0.7 3 hr 9.3 5.1 86.6 4.0 43.3 20.0 0.13 1.4 2.9 #2 1.0 3 hr 8.9 7.7 87.7 6.6 41.5 18.9 0.19 12.2 4.6 #3 1.0 1 hr 7.8 6.1 88.7 6.9 51.1 21.8 0.17 1.8 3.9] 11 Subsequent tests were then conducted by producing a rougher concentrate in a conventional rougher flotation stage followed by acid conditioning of the rougher concentrate under varying acid/pH conditions and times. The acid conditioned rougher concentrate is then floated during a cleaner flotation stage, without the addition of additional reagents, to produce a final cleaner concentrate. The results of these three tests are included in Table 3.

It will be appreciated from the results of all of these examples that an increased nickel recovery is experienced with acid conditioning of the rougher concentrate. This is "'.achieved with only a very slight decrease in the nickel Grade of the cleaner concentrate. Therefore, it is oo** apparent that a combination of both relatively long 15 conditioning times at relatively low pH produces high nickel recoveries and consequently a throwaway cleaner tail Grade.

V Now that several examples of the present invention have been described in some detail it will be apparent to those 20 skilled in the relevant arts that the process for the improved flotation of valuable sulphide minerals has at least the following advantages over the admitted prior art: a greater recovery of valuable sulphide minerals is achieved in the final concentrate; an improved selectivity between valuable sulphide minerals and gangue minerals is achieved; the speed at which valuable and gangue minerals separate is faster; and flotation may be conducted without the use of collector agents and/or depressant agents thereby reducing cost.

12 The present invention is not limited to the examples described above and numerous variations and modifications can be made to the process for the improved flotation of valuable sulphide minerals which still remain within the ambit of the present invention. For example, other metallic sulphide ores such as copper, lead, zinc, molybdenum, and native gold and silver are amenable to the process of the present invention. Furthermore, the present invention does not exclude the addition of collector and/or depressant agents but rather reduces the necessity for their use. The pH of the pulp may be achieved through other means other than the addition of sulphuric acid.

o o :i The preceding examples of the present invention are provided to illustrate specific embodiments of the 15 invention and are not intended to limit the scope of the process of the invention.

ee B.

Claims (9)

1. 2. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in claim 1 wherein process step involves adjusting the pH of the pulp to a value of between approximately 0.5 to less than 20 3. A process for the improved flotation of valuable oo sulphide minerals contained in a pulp as defined in either of claims 1 or 2 wherein process step involves conditioning the pulp with an acidic solution for a predetermined period. oooo 25 4. A process for the improved flotation of valuable *o*o sulphide minerals contained in a pulp as defined in claim 3 S• wherein the predetermined period will be from between approximately 1 minute to 3 hours.
2. 5. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in either of claims 3 or 4 wherein the acidic solution used to condition the pulp is sulphuric acid at an addition rate of between approximately 5 to 50 kg of sulphuric acid per tonne of sulphide ore. 14
3. 6. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in any one of the preceding claims further involving the addition of a depressant agent to the pulp, said depressant agent added in a reduced amount compared with conventional flotation processes, so that during flotation in process step (b) depression of the gangue minerals is promoted thus minimising the recovery of gangue minerals in the concentrate.
4. 7. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in claim 6 99*9 wherein the depressant agent includes sodium t. carboxymethylcellulose (CMC) or a derivative thereof. A process for the improved flotation of valuable 15 sulphide minerals contained in a pulp as defined in any one of the preceding claims wherein process step is performed subsequent to a conventional flotation stage so that adjustment of the pH of the pulp in process step (a) involves adjustment of a flotation concentrate recovered 20 from the conventional flotation stage. see* sees
5. 9. A process for the improved flotation of valuable S, sulphide minerals contained in a pulp as defined in any one of claims 1 to 7 wherein process step is performed subsequent to milling of the sulphide ore.
6. 10. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in any one of the preceding claims involving at least two stages of flotation, namely a rougher and cleaner stage.
7. 11. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in any one of the preceding claims, said pulp being formed from a serpentine-hosted nickel sulphide ore containing 15 pentlandite, millerite, heazlewoodite, chalcopyrite, pyrrhotite, pyrite and magnesium-containing gangue minerals including serpentine.
8. 12. A process for the improved flotation of valuable sulphide minerals contained in a pulp as defined in claim 11 wherein the valuable sulphide minerals include pentlandite and chalcopyrite and the magnesium-containing gangue minerals include brucite and serpentine.
9. 13. A process for the improved flotation of valuable sulphide minerals contained in a pulp, said process substantially as herein described with reference to and as illustrated in the accompanying flowsheets. 0 DATED THIS 20TH DAY OF MAY, 1997 WMC RESOURCES LIMITED By Its Patent Attorneys: GRIFFITH HACK Fellows Institute of Patent Attorneys of Australia G*