AU691312B2 - Physical separation processes for mineral slurries - Google Patents

Description

WO 96101150 PCTIAU95O00403 1 PHYSICAL SEPARATION PROCESSES FOR MINERAL SLURRIES.

Field of the Invention.

This invention relates to the physical separation of minerals and, in particular, to the separation of minerals of different mineralogical character.

Background of the Invention.

There exists a number of non-sulphide minerals, including carbonaceous minerals (e.g graphite, carbon based residues as exist in Mt Isa, Australia ore bodies), talcose minerals (e.g talc, brucite etc which are associated with Western Australian nickel deposits and the Woodlawn, New South Wales, Australia base metal deposit) as well as amphiboles that have naturally hydrophobic surfaces.

As a result, these "gangue" minerals float readily and are very difficult to separate from other valuable minerals, notably the sulphide minerals (e.g chalcopyrite (CuFeS 2 pentlandite (Ni,Fe) 9

S

8 and sphalerite (ZnS)).

When present in mineral concentrates, these "gangue" minerals often attract penalty charges at the smelter and, indeed, may be the cause of rejection of the concentrate by the smelter.

Two approaches to this problem exist in practice, namely to minimise the flotation of the non-sulphide "gangue" minerals using specific reagents or, alternatively, to encourage flotation of the "gangue" minerals in a pre-flotation step prior to the flotation of the desired minerals.

In the first approach, reagents such as depressants (guar gum, CMC, etc) or dispersants (e.g sodium silicate, etc.) are employed to minimise the flotation rate of the non-sulphidic minerals. While successful to some extent, the use of these reagents is non-specific and adversely affects the flotation behaviour of the sulphide minerals in terms of metallurgy as well as froth structure. In addition, such reagents are costly and, if it were possible, would be avoided.

Furthermore, the use of such reagents not only adversely affects flotation behaviour, it affects downstream operations such as dewatering and settling of the minerals. Additionally, and particularly with depressants, there is a requirement to add more reagent at each stage of the separation process.

In the second approach, a separate flotation system is dedicated to the recovery of the naturally floating mineral. Reagents are added to prevent the flotation of the valuable sulphide minerals, however with varying degrees of success anc. losses due to flotation and entrainment may occur. Inevitably, there will be at least some loss of the valuable by undesired flotation mineral with the gangue recovered from the pre-flotation system. Such losses represent an economic disincentive and would ideally be avoided.

Summary of the Invention In a first aspect, the present invention provides a flotation process for the separation of a mineral of non-sulphidic character from a mineral of sulphidic character characterised in that a slurry containing a mixture of the minerals is subjected to a sequence of mineral dressing operations in which a non-oxidising gas or gas mixture is added to the slurry to achieve an electrochemical potential conducive to the separation of the minerals by flotation.

In a second aspect, the present invention provides a flotation process for the separation of a mineral having a natural tendency to float from a mineral of sulphidic character characterised in that a slurry containing a mixture of the minerals is subjected to a sequence of mineral dressing operations in which a non-oxidising gas or gas mixture is added to the slurry to achieve an electrochemical potential conducive to the separation Sof the minerals by flotation.

20 In a preferred embodiment, a reducing agent is added in combination with the nonoxidising gas or gas mixture to the slurry.

Conveniently, the non-oxidising gas is selected from the group consisting of inert gases such as nitrogen and argon and gases such as carbon dioxide. Gases such as V. nitrogen and sulphur oxides eg sulphur dioxide, nitrogen dioxide are also included.

Mixtures of these gases may also be used and the other reducing agent is preferably :selected from the group consisting of ammonium sulphide, ammonium hydrosulphide, sodium sulphide, sodium hydrosulphide, potassium sulphide, potassium hydrosulphide or a sulphide or hydrosulphide of other alkali or alkaline earth metals. Other sulphide, sulphite or sulphoxy agents may also be employed (eg hydrogen sulphide, sulphur dioxide, dithionate salts).

The mineral of non-sulphidic character may be an oxide, oxidic or carbonaceous mineral of which examples are talc, graphite, brucite and amphiboles, which may have tendency to float in the absence of specific collectors.

The mineral of sulphidic character may contain base metal sulphides including copper, zinc, lead or nickel sulphides and may, for example, be chalcocite, chalcopyrite, pentlandite, galena or sphalerite.

Naturally floating sulphides, such as molybdenite, and other species such as metallic gold may also be amenable to such separation and treatable by the process according to a second aspect of the present invention.

Detailed Description of the Invention In one embodiment of the process, a mineral ore containing both minerals of sulphidic and non-sulphidic character is crushed, slurried, ground and conditioned with a non-oxidising gas or gas mixture. Optionally, conditioning with the non-oxidising gas or gas mixture may be accompanied by conditioning with a reducing agent, for example, sodium sulphide to depress the sulphidic mineral and promote flotation of the nonsulphidic mineral and floated.

The flotation gas may ideally be a non-oxidising gas, such as nitrogen. By combined influence of the reducing agent and the non-oxidising gas, however this is achieved, a selectivity of separation may be achieved that is not known in conventional 20 processes.

During milling, mineral surfaces are preferably exposed to a reducing environment through optional milling in a non-oxidising gas atmosphere that maintains their sulphidic character and maintains the efficiency of the reducing agents. As a result, the reducing agent has better capability in terms of ensuring depression of the valuable sulphidic mineral. In such a way, loss of this mineral to the prefloat non-sulphidic "gangue" mineral stream is minimised.

For example, the reducing agent and non-oxidising gas may both be added at the comminution or grinding stage or the reducing agent can be added later in a conditioning stage. Further, while oxidation of sulphidic mineral surfaces is certainly suppressed by introduction of a non-oxidising gas during the comminution or grinding stage, this is not .Z mandated by the present invention.

-4- In this way too, an "activation" phenomenon, whereby gangue is surrounded by a layer of floatable sulphide, for example copper sulphide, thus causing the loss of the mineral in the gangue stream may be avoided. Although the addition of a sulphide depressant may assist in this respect, the avoidance of exposure of fireshly created sulphidic mineral surfaces to an oxidising environment can only further assist in this process.

Furthermore, a synergy is attainable by use of the non-oxidising gas in that the consumption of the reducing agent, generally both an expensive chemical, or at least one that causes inconvenience in terms of both the requirement of supply to remotely located concentrators as well as mixing and preparation, may be reduced with positive economic effects.

The addition of non-oxidising gases, such as nitrogen, and reducing agents, such as sodium sulphide, whose reducing properties in terms of their effect on slurry electrochemical potential allows for good cuntrol of the electrochemical potential, is advantageous to good separation selectivity and efficiency.

The slurry may be conditioned with the non-oxidising gas and reducing agent either in the same or discrete conditioning stages post-milling and prior to flotation or during flotation itself. The agents may be added in amounts to achieve a desired electrochemical potential.

20 It is not intended to place any limitation upon the point of introduction of the reagents hereabove mentioned.

.With respect to the continuity of the process, the process may be conducted under batch, semi-batch or continuous conditions. However, in practice, the process will generally be conducted under continuous conditions with single or multiple conditioning and/or flotation stages. The number of conditioning and/or flotation stages selected should be sufficient to achieve the desired degree of separation of the oxidic and sulphidic materials and may be calculated by appropriate calculation and/or trial and error for a particular ore body.

In its broadest form the reducing agent is not required. This would occur in cases where WO 96/01150 PCT/AU95/00403 the addition of nitrogen alone is sufficient to enable attainment of a suitably low slurry electrochemical potential to achieve the non-sulphidic mineral from the sulphidic mineral.

However, cases will undoubtedly arise where the use of a further reducing agent with enhanced reducing properties to nitrogen must be adopted.

In this respect, the addition of nitrogen may only enable a first threshold electrochemical potential value to be reached. This first threshold electrochemical potential value may be sufficiently high as to not result in the degree of selectivity of separation required to enable production of an economically viable non sulphide mineral concentrate. Losses of valuable mineral to the oxidic or other pre-float product may also be unacceptable. Then, a reducing agent, such as those described above, may be required to ensure that electrochemical potential is reduced to a value below the first threshold value outlined above and that the loss of valuable minerals is reduced to an acceptable level.

Cases may also arise where it is desired to further promote the separation of the non-oxidic mineral by various collectors. While this is unlikely in the cases of naturally floating minerals such as talc, it is not intended to preclude the use of such agents from the scope of the present invention.

It will further be appreciated that the rate of addition of nonoxidisable gas, pH and temperature at which the preflotation takes place may be of importance and therefore systems which allow appropriate control over gas addition, alkalinity and temperature may be required.

Example 1.

By way of example, there follows a description of separation of a talc gangue mineral from a pentlandite mineral now follows.

The pentlandite ore is crushed and then finely ground in a ball mill circuit to which nitrogen is injected to ensure the provision of a non-oxidising atmosphere and ensure avoidance of oxidation of pentlandite mineral surfaces.

Additionally, where iron balls are used, corrosion and interference reactions of iron with the pentlandite under oxidising conditions are avoided.

The sodium sulphide was added at an addition rate of 0.1-0.5g/kg of pentlandite ore at a conditioning point located after the ball mill circuit. The WO 96/01150 PCTIAU95100403 6 pulp was conditioned for five minutes. Following this step, the flotation was conducted, for example, in Denver cells under nitrogen with otherwise standard conditions. This enables recovery of the "gangue" prefloat. A suitable addition rate for nitrogen or inert gas in the flotation stage is 500 I/hour with an agitation speed for the turbine of the Denver cell of 1200 rpm.

This process enabled substantial recovery of gangue m,nerals with a very low quantity of entrained pentlandite.

Example 2.

By way of a second example, there follo.vs a description of separation of a non-sulphidic talcose mineral, predominately talc, from a polymetallic ore containing copper, lead and zinc sulphides. The ore contains magnesia and silica in respective amounts of 4.76% and 27.2% by weight.

A 1 kg charge of crushed ore was slurried in site process water to obtain pulp density 60 wt% solids and milled in a stainless steel rod mill employing stainless steel rods to achieve P75 of approximately 53 microns.

The milled slurry was then repulped to pulp density 35 wt% solids in a 2.7 litre standard "Agitair" laboratory flotation cell operated at 1300 rpm with purging of nitrogen in a conditioning phase. Nitrogen flotation tests were conducted under three conditions, viz: no reagent addition (standard practice) sodium sulphide 1 kg/t milled ore and nitrogen to achieve slurry electrochemical potential (Eh) -25 to -40 mV sodium dithionate 1 kg/t milled ore and nitrogen to achieve Eh -25 to -40 mV.

In each case nitrogen was employed as the flotation gas. Further, a total of five concentrates were removed at 1, 2, 4, 6 and 8 respectively minutes and assayed for copper, lead and zinc content using standard assay techniques.

The data is tabulated for duplicate tests in the form of cumulative weight recovery of copper, lead and zinc recovered in the talc mineral floated in the example flotation process. The less the proportion of the metals recovered, the more effective the flotation separation.

Test A Standard Practice.

Con No Cumulative Weight Percent (Wt%Recovery) Cumulative Cu(%) Metal Recovery Zn(%) Cumulative Weight Percent (Wt%Recovery) A2 Cumulative Metal Recovery Zn(%) 3 4 S 5 3.94 6.78 10.44 12.43 15.54 4.79 10.49 21.41 29.30 38.66 2.51 4.73 8.32 10.77 1.18 2.17 3.73 .82 3.6 6.56 11.10 12.82 5.44 13.85 29.92 43.12 51.27 2.31 4.48 7.79 10.93 14.02 1.07 2.09 3.67 5.18 6.55 16.09 6.66 1 Test B NagS/Nitrogen 4.99 Con No Cumulative Weight Percent (Wt%Recovery) 3.56 5.47 7.41 8.60 9.61 Cumulative Cu(%) 1.50 2.51 3.84 4.81 5.71 Metal Recovery Zn(%) B2 Cumulative Cumulative Metal Recovery Weight Percent Zn(%) (Wt%Recovery) 1.64 2.70 4.07 5.14 6.23 0.9 1.65 2.54 3.26 3.98 3.78 5.22 6.95 8.21 9.51 1.74 2.57 3.79 4.49 5.96 1.98 2.85 4.12 5.28 6.74 1.18 1.73 2.56 3.32 4.31 Test C Na S 2 g4/Nitroaen Con No Cumulative Weight Percent (Wt%Recovery) C1 Cumulative Metal Recovery Zn(%) Cumulative Weight Percent (Wt%Recovery) C2 Cumulative Metal Recovery Zn(%) 1 3.87 1.62 2.14 0.89 3.37 0.92 1.57 0.70 2 5.49 2.42 3.18 1.35 4.96 1.41 2.46 1.09 3 7.89 3.85 4.93 2.15 6.94 2.15 3.78 1.69 4 9.59 5.07 6.52 2.95 8.25 2.74 4.84 2.20 10.75 5.91 7.69 3.62 9.61 3.42 6.12 2.88 The test data indicate that there is less metal loss to the talc component of the mineral when Na 2 S/nitrogen or Na 2

S

2 04/nitrogen combinations are employed.

s c\ a

Claims (19)

1. A flotation process for the separation of a mineral of non-sulphidic character from a mineral of sulphidic character characterised in that a slurry containing a mixture of the minerals is subjected to a sequence of mineral dressing operations in which a non- oxidising gas or gas mixture is added to the slurry to achieve an electrochemical potential conducive to the separation of the minerals by flotation.

2. The process of claim 1 wherein a reducing agent is added in combination with the non-oxidising gas or gas mixture to the slurry.

3. The process of claim 1 or 2 wherein the non-oxidising gas is selected from the group consisting of nitrogen, argon, carbon dioxide and sulphur dioxide and mixtures thereof.

4. The process of claim 2 wherein said reducing agent contains at least one of sulphur and oxygen. The process of claim 4 wherein said reducing agent is a sulphide of an alkali or alkaline earth metal.

6. The process of claim 3 wherein said reducing agents is selected from the group consisting of ammonium sulphide, ammonium hydrosulphide, sodium sulphide, sodium hydrosulphide, sodium dithionate, potassium sulphide, potassium hydrosulphide, potassitun dithionate. o 20 7. The process of claim 1 wherein said mineral of sulphidic character is a base metal sulphide.

8. The process of claim 7 wherein said mineral of sulphidic character is selected from the group consisting of copper, zinc, lead or nickel sulphides and mixture thereof.

9. The process of claim 7 wherein said base metal sulphide is chalcocite, chalcopyrite, pentlandite, galena or sphalerite.

10. The process of claim 1 wherein said mineral of non-sulphidic character is selected S*i from the group consisting of oxide, oxidic and carbonaceous minerals.

11. The process of claim 10 wherein said mineral of non-sulphidic character is selected from the group consisting of talcose minerals, graphite, brucite, amphiboles and mixtures thereof. F,3 12. The process of claim 11 wherein talcose minerals include talc. s

13. The process of claim 1 wherein said non-oxidising gas is selected from the group consisting of nitrogen, argon, carbon dioxide and mixtures thereof.

14. The process of claim 1 wherein said non-oxidising gas is an oxide of sulphur or nitrogen.

15. The process of claim 14 wherein said non-oxidising gas is sulphur dioxide.

16. The process of claim 2 wherein said slurry is conditioned with the reducing agent and non-oxidising gas in the same conditioning stage.

17. The process of claim 2 wherein said slurry is conditioned with the reducing agent and non-oxidising gas in respective discrete conditioning stages.

18. The process of claim 2 wherein said slurry is conditioned with the reducing agent and non-oxidising gas in a flotation stage.

19. The process of claim 2 wherein the reducing agent and/or non-oxidising gas are added in accordance with monitored electrochemical potential of the slurry. A product of the flotation process as claimed in any one of claims 1 to 18.

21. A non-oxidising gas introduced to a slurry containing a mixture of sulphidic and non-sulphidic minerals in combination with a reducing agent during a process for the flotation separation thereof.

22. A reducing agent introduced to a slurry containing a mixture of sulphidic and non- sulphidic minerals in combination with a non-oxidising gas during a process for the o0 20 flotation separation thereof. *23. A flotation process for the separation of a mineral having a natural tendency to float from a mineral of sulphidic character characterised in that a slurry containing a mixture of the minerals is subjected to a sequence of mineral dressing operations in which a non-oxidising gas or gas mixture is added to the slurry to achieve an electrochemical potential conducive to the separation of the minerals by flotation. S24. The process of claim 23 wherein a reducing agent is added in combination with the 0 non-oxidising gas or gas mixture to the slurry. The process of claim 23 or 24 wherein said mineral having a natural tendency to float is molybdenite or metallic gold. 11

26. A flotation process substantially as hereinbefore described with reference to any one of the accompanying examples. DATED this 25th day of July 1997 BOC GASES AUSTRALIA LIMITED Attorney: PAUL G. HARRISON Fellow Institute of Patent Attorneys of Australia of SHELSTON WATERS a a. *9 a* a a *o I INTERNATIONAL SEARCH REPORT International Application No. PCT/AU 95/00403 A. CLASSIFIC TION OF SUBJECT MATTER Int Cl 6 B03B 1/04, BO3D 1/02 According to International Patent Classification (IPC) or to both national classification and IPC B. FIELDS SEARCHED Mitnmum documentation searched (classification system followed by classification symbols) IPC B03B 1/04, B03D 1/02, 103:04 Docamentation searched other than minimum documentation to the extent that such documents are included in the fields searched AU: IPC as above Electronic data base consulted during the international search (name of data base and, where practicable, search terms used) DERWENT C. DOCUMENTS CONSIDERED TO BE RELEVANT Category* Citation of document, with indication, where appropriate, of the relevant passages Relevant to claim No. A US 4457850 A (HOLGER TESMANN et al) 3 July 1984 A EP 597522 Al (METALLGESELLSCHAFT AG) 2 November 1993 A AU 24695/71 (453363) A (ANACONDA COMPANY) 27 July 1972 E Further documents are listed in the continuation of Box C See patent family annex Special categories of ited documents: later document published OtRer the international filing date or document defining the general state of the art which is priory date and not in conflict with the application but cited to not considered to be of particular relevance understand the principle or theory underlying the invention earlier document but published on or after the document of particular relevance; the claimed invention cannot international filing date be considered novel or cannot be considered to involve an document which may throw doubts on priority claim(s) inventive Atep when the document is taken alone or which is cited to establish the publication date of document of particular relevance; the claimed invention cannot another citation or other special reason (as specified) be considered to involve an inventive step when the document is document referring to an oral disclosure, use, combined with one or more other such documents, such exhibition or other means combination being obvious to a person skilled in the art document published prior to the international filing document member of the same patent family date but later than the priority date claimed Date of the actual completion of the international search Date of mailing of the international search report 0 ctober 1995 12 Ocr-o I QE c19 Name and mailing address of the ISA/AU Authorized officer AUSTRALIAN INDUSTRIAL PROPERTY ORGANISATION G. PO BOX 200 WODEN ACT 2606 ASOKA DIAS-ABEYG(NAWARDENA AUSTRALIA Facsimile No.: (06) 285 3929 Telehone No.: (06) 283 2141 No.: (06) 283 Form PCT/ISA/210 (second sheet) (July 1992) coprmc I A 0 INTERNATIONAL SEARCH REPORT International Application No. IC (Continuation) DOCUMENTS CONSIDERED TO BE RELEVANT PCT/AU 95/00403 Category* Citation ol document, with indication, wherc appropriate, of the relc, .issagcs Relevant to claim No. A Derwent Soviet Inventions Illustrated, Section 1, chemical, issucd 9 September 1975, Metallurgy, p.3, SU 405247 (GLAZUNOV et 10 December 1974 A Derwent Abstract Accession No. 87-019670/03, Class P41, .JP,A, 86/059183-B (DOWA MINING CO LTD) 15 December 1986 Form PCT/ISA/2 10 (continuation of second sheet) (July 1992) coprmce INTERNATIONAL SEARCH REPORT International Applicauon No. PCT/AU 95/00403 This Annex lists the known publication level patent family members relating to the patent documents cited in the above-mentioned international search report. The Australian Patent Office is in no way liable for these particulars which are merely given for the purpose of information. Patent Document Cited in Search Patent Family Meiv'bcr Report US 4457850 CA 1207092 EP 108914 AU 559346 EP 597522 AU 50588/93 AU 661618 DE 4238244 US 5439115 END OF ANNEX Form PCT/ISA/210 (patent family annex) (July 1992) coprm