AU729971B2 - Method of reducing lime/pH modifying agent in the flotation of copper 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 S Actual Inventors: David William CLARK and Andrew James Haigh NEWELL Address of Service: BALDWIN SHELSTON WATERS 60 MARGARET STREET SYDNEY NSW 2000' Invention Title: "METHOD OF REDUCING LIME/pH MODIFYING AGENT IN THE FLOTATION OF COPPER MINERALS" Details of Associated Provisional Application No. PO 7883 dated 14 July, 1997 The following statement is a full description of this invention, including the best method of performing it known to us:- -2- TECHNICAL FIELD The present invention relates to the physical separation of minerals and in particular the separation of minerals with different mineralogical character.

BACKGROUND ART In the flotation separation of various minerals, pH plays an important role.

Indeed, where possible flotation is carried out in an alkaline medium as most collectors, including xanthates, are stable under these conditions and the corrosion of cells, pipework etc is minimised. Generally alkalinity is controlled by the addition of lime, sodium carbonate (soda ash) and to a lesser extent sodium hydroxide or ammonia.

10 Acidic compounds such as sulphuric or sulphurous acids are used where a decrease in pH is required.

Generally lime is used to regulate pulp alkalinity since it is cheap and readily available. It is normally used in the form of milk of lime, an aqueous suspension of calcium hydroxide particles. The lime, or alternatively soda ash, is often added to the slurry prior to flotation to precipitate heavy metal ions from solution.

These pH altering chemicals are often used in significant amounts. Although they are cheaper than collectors and frothers the overall cost is generally higher with pH regulators per tonne of ore treated than with any other processing chemical. Indeed, the cost of lime for example in many sulphide mineral flotation operations is roughly double that of the collector used.

In conjunction with an appropriate xanthate collector, sufficient alkali will depress almost any sulphide mineral and for any concentration of a particular collector, there is a pH value below which any given mineral will float and above which it will not float.

-3- This of course allows an operator to selectively float various sulphide minerals from an ore slurry.

The "critical pH" value of any ore depends on the nature of the mineral, the particular collector and its concentration and the temperature.

Additionally, lime by itself, or in conjunction with a sulphoxy reagent, acts to depress certain minerals. For example in complex copper/lead/zinc ores, lime with or without sulphoxy reagents acts to depress sphalerite, pyrite and pyrrhotite.

A typical flow chart for a conventional flotation process using lime for pH o adjustment is shown in figure 1. The slurry is firstly mixed with lime in the milling i' circuit 10. A further pH adjustment 12 may be included where pH is increased to around 9-11, preferably 10.5, by the further addition of lime. A collector and frother may then be added in a reagent conditioning stage 14 followed by the flotation stage(s) 16.

There are, however, difficulties associated with the conventional use of lime and other alkaline agents to alter the pH of the slurry entering the flotation circuit. Firstly, S 1. 15 reducing the quantity of lime required will reduce the cost associated with the preparation of the slurry prior to flotation.

Further, calcium ions, present in the lime, can deposit onto the valuable mineral reducing their floatability.

It is an object of the present invention to overcome at least some of the difficulties of the prior art or at least provide a commercial alternative to the prior art.

DISCLOSURE OF THE INVENTION In a broad aspect, the present invention provides a method of reducing the consumption of alkaline pH modifier in a mineral separation circuit employing a -4sulphoxy radical containing reagent wherein prior to or simultaneously with the addition of said sulphoxy radical containing reagent, an inert/non-oxidising gas is added to the mineral separation circuit in a quantity sufficient to achieve a chemical environment conducive to flotation separation of minerals.

The present applicants have found that conditioning a slurry or flotation concentrate with an inert/non-oxidising gas and a sulphoxy compound provides a chemical environment conducive to the flotation separation of the valuable minerals from the non-valuable minerals without the need for, or at least a reduction in, the addition of alkaline pH modifying agents including lime and derivative compounds such i "10 as cement, clinker, quicklime, hydrated lime, limestone etc as well as soda ash, caustic soda etc.

S* The process is particularly suitable for slurries or flotation concentrates having a mixture of valuable minerals including sulphidic copper minerals or sulphidic and nonsulphidic copper minerals, and non-valuable sulphidic iron minerals (particularly pyrite) 15 and non-sulphidic "gangue" materials.

BRIEF DESCRIPTION OF THE DRAWINGS So that the present invention may be more clearly understood it will now be described with reference to the accompanying drawings in which: Figure 1 is a flow sheet of conventional flotation process using lime for the pH adjustment.

Figure 2 is a flow sheet of a flotation circuit according to a first embodiment of the present invention.

I.

Figures 3 and 4 are flow sheets of flotation circuits according to second and third embodiments of the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION As shown in figure 2 the slurry is firstly passed through milling circuit 100 to reduce the particle size to a level suitable for subsequent flotation. The milled slurry is then conditioned for between 1 and 10 minutes, preferably 2 to 5 minutes, with nitrogen in a nitrogen conditioning stage 120. In a further sulphoxy reagent stage 140 for example sodium metabisulphate (SMBS) is added and the nitrogen conditioning continued for between 1 and 10 minutes, preferably 2 to 5 minutes. Nitrogen is then 10 stopped.

S. Appropriate collectors and frothers for effecting flotation of the slurry may then be :added in reagent conditioning stage 160 and the slurry conditioned for one minute. The conditioned slurry is then floated in flotation stage(s) 180 with air to effect recovery of the valuable minerals from the non-valuable minerals.

15 Any suitable inert/non-oxidising gas may be used in conjunction with the sulphoxy agent however nitrogen, argon, neon, carbon dioxide, sulphur dioxide, methane, ethane or propane and/or admixtures thereof are preferred.

Similarly, as will be clear to person skilled in the art, there are a wide variety of suitable sulphoxy agents for use in conjunction with the present inventive process.

Sodium sulphite, sodium hydrogen sulphite, sodium metabisulphite, sodium bisulphite, sulphur dioxide gas or solution, sulphite agents, K, Ca, NH 4 salts may be used.

-6- The present inventive process is suitable for a wide variety of ores including but not limited to sedimentary copper deposits, copper skams, porphyry copper/molybdenum/gold deposits and supergene enrichments.

The duration and intensity of the nitrogen conditioning step will depend upon a number of factors including the type of ore undergoing flotation, the amount and type of sulphoxy agent added in conjunction with the nitrogen conditioning and the dissolved oxygen content of the slurry.

prior to the inventive process. Accordingly it should be understood that alkaline pH S" 10 modifying agents may also be used with the present inventive process although the S. amounts required will be reduced as compared to conventional processes.

It is also possible that prior to addition of the collector and flotation but after the nitrogen/sulphoxy agent conditioning step, the slurry may require oxidative gas conditioning in stage 150 to a particular dissolved oxygen concentration eg DO 2 ppm "15 or electrochemical potential which is suitable for flotation of the particular sulphide mineral.

For reasons that are not as yet entirely understood, the present inventive conditioning step reduces and in some cases eliminates the need for lime addition. Even in the case where the use of lime is not completely avoided, there is a significant reduction in the lime required to effect flotation separation of the valuable minerals.

As mentioned above, this lower lime addition reduces the quantity of calcium ions in the slurry which may deposit onto the valuable minerals thereby reducing their floatability.

Figure 2 shows the present inventive process when used in the rougher/scavenger flotation stages however it should also be understood that the present invention can be used in the cleaning stages of a flotation circuit as shown more clearly in figure 3. In this embodiment, stages 10-16 are of conventional design. Cleaning stages 18 and however, are in accordance with the present inventive process in which an inert/nonoxidising gas eg nitrogen is added prior to or simultaneously with the addition of a sulphoxy radical containing reagent.

In still a further embodiment, as shown in figure 4, the use of the present inventive process in the rougher/scavenger flotation stages offers the opportunity to cost i 10 effectively apply different chemistry to the subsequent cleaning stages.

As shown in figure 4, the rougher/scavenger flotation stages 100-180 are in S"accordance with the present inventive process. Prior to cleaning stage 220, a conventional pH conditioning stage 200 may be provided in which lime or a similar pH modifying agent is added to the slurry with beneficial results.

Lastly, a surprising result achieved by the present invention is the increase in molybdenum flotation for copper/molybdenum ore types. The applicants have found that conducting flotation at a lower pH ie with less lime addition, is more conducive to molybdenum flotation. Accordingly, if it is desired to float molybdenum from a complex ore it is no longer necessary to add acidic compounds to lower the pH to a suitable level for molybdenum flotation.

The following examples serve to further clarify the present invention.

-8- EXAMPLE 1: STANDARD CONDITIONS pH 10.4 A test was conducted in a similar manner to that shown in figure 1 where a 1 kg charge of crushed copper porphyry ore containing copper minerals chalcocite and chalcopyrite assaying 0.6 percent copper was slurried in water to obtain a pulp density 55 wt solids and milled in a stainless steel rod mill employing stainless steel rods to achieve P80 of approximately 300 microns in the presence of 1 gram of lime. The milled slurry was then transferred to a 2.5 litre Denver flotation cell and diluted to approximately 35 percent solids with water. The pH of the slurry was measured and no addition lime was required. The appropriate quantities of collector and frother were then 10 added and the slurry was conditioned for 1 minute. At the completion of conditioning flotation with air was commenced and three concentrates were produced from 3, 6 and 9 minutes respectively of flotation. Additional collector was added after the first and second concentrates had been produced. The combined concentrates and flotation S tailings were filtered, dried, weighed and the copper contents determined by assay.

15 EXAMPLE 2: pH 9.2 A test was conducted in a similar manner to that shown in figure 2 and using the same ore and equipment as that described in Example 1 and the same total collector and frother additions.

After milling without lime addition, the slurry was transferred to the flotation cell.

The pH was measured and sufficient lime added to achieve a pH of 9.2 (approximately 750 gpt). Nitrogen gas was then added at 4 1pm until the slurry dissolved oxygen content was approximately 1 ppm. Then 100 gpt of sodium mietabisuilpiite (SMBS) was added as a solution and the slurry was conditioned for 5 minutes while maintaining Rnitrogen addition at 4 1pm. The appropriate quantities of collector and frother were then -0•0 -9added and the slurry was conditioned for 1 minute. At the completion of conditioning flotation with air was commenced and three concentrates were produced from 3, 6 and 9 minutes respectively of flotation. Additional collector was added after the first and second concentrates had been produced. The combined concentrates and flotation tailings were filtered, dried, weighed, and the copper contents determined by assay.

EXAMPLE 3: pH A test was conducted in a similar manner to that shown in figure 2 and using the same ore and equipment as that described in test 1 and the same total collector and I::frother additions.

10 After milling without lime addition, the slurry was transferred to the flotation cell.

The pH was measured and sufficient lime added to achieve a pH of 7.5 (approximately 500 gpt). Nitrogen gas was then added at 4 Ipm until the slurry dissolved oxygen content was approximately 1 ppm. Then 50 gpt of SMBS was added as a solution and S* the slurry was conditioned for 5 minutes while maintaining nitrogen addition at 4 1pm.

1. 15 The appropriate quantities of collector and frother were then added and the slurry was conditioned for 1 minute. At the completion of conditioning flotation with air was commenced and three concentrates were produced from 3, 6 and 9 minutes respectively of flotation. Additional collector was added after the first and second concentrates had been produced. The combined concentrates and flotation tailings were filtered, dried, weighed, and the copper contents determined by assay.

RESULTS

The results of the evaluation are summarised as follows: TEST SMBS LIME FLOTATION Cu ASSAY Cu ADDITION ADDITION pH

RECOVERY

gpt gpt 1 0 1000 10.4 7.41 68.6 2 100 750 9.2 6.02 72.8 3 50 500 7.5 7.03 73.7 The results clearly show that lime addition can be reduced substantially while flotation metallurgy as shown by copper recovery has increased.

The following test example was conducted where no lime was added: 5 EXAMPLE 4: pH A test was conducted in a similar manner to that shown in figure 2 and using the same ore and equipment as that described in Example 1 and the same total collector and frother additions.

After milling without lime addition, the slurry was transferred to the flotation cell.

10 The pH was measured, for this test no lime added. Nitrogen gas was then added at 4 1pm until the slurry dissolved oxygen content was approximately 1 ppm. Then 200 gpt of SMBS was added as a solution and the slurry was conditioned for 5 minutes while maintaining nitrogen addition at 4 1pm. The appropriate quantities of collector and frother were then added and the slurry was conditioned for 1 minute. At the completion of conditioning flotation with air was commenced and three concentrates were produced from 3, 6 and 9 minutes respectively of flotation. Additional collector was added after the first and second concentrates had been produced. The combined concentrates and flotation tailings were filtered, dried, weighted, and the copper contents determined by assay.

11 The results of test 4 as compared to the other tests are summarised as follows: TEST SMBS LIME FLOTATION Cu ASSAY Cu ADDITION ADDITION pH RECOVERY gpt gpt 1 0 1000 10.4 7.41 68.6 2 100 750 9.2 6.02 72.8 3 50 500 7.5 7.03 73.7 4 200 0 5.0 7.76 59.0 0 0 0 00 While for the ore tested, the complete elimination of lime and flotation at pH 5.0 resulted in significantly poorer metallurgy, there it would appear that for some ores lime can be eliminated. This could depend on the pH of the slurry.

The present inventive process may be used with conventional apparatus which will be well-known to persons skilled in the art and it will be understood that the present inventive process may be embodied in forms other than that shown without departing from the spirit or scope of the invention.

Claims (14)

1. A method of reducing the consumption of alkaline pH modifier in a mineral separation circuit employing a sulphoxy radical containing reagent wherein prior to or simultaneously with the addition of said sulphoxy radical containing reagent, an inert/non-oxidising gas is added to a slurry in the mineral separation circuit in a quantity sufficient to achieve a chemical environment conducive to the flotation separation of minerals.

2. A method as claimed in claim 1 wherein the inert/non-oxidising gas is selected from the group consisting of nitrogen, argon, neon, carbon dioxide, sulphur dioxide, 10 methane, ethane or propane and/or admixtures thereof.

3. A method as claimed in claim 1 or claim 2 wherein the sulphoxy radical containing S: reagent is selected from the group consisting of sodium sulphite, sodium hydrogen sulphite, sodium metabisulphite, sodium bisulphite, sulphur dioxide gas or solution, sulphite agents and K, Ca, NH4 salts thereof, and admixtures thereof. 15

4. A method as claimed in any one of the previous claims wherein the inert/non- oxidising gas is added to the mineral separation circuit to provide a dissolved oxygen concentration or electrochemical potential in the slurry which is suitable for the flotation of the mineral.

A method as claimed in any one of the preceding claims wherein the slurry is conditioned with an inert/non-oxidising gas for between 1 and 10 minutes.

6. A method as claimed in any one of the preceding claims wherein the slurry is conditioned with an inert/non-oxidising gas for between 2 and 5 minutes. -13-

7. A method as claimed in any one of the preceding claims wherein the slurry is conditioned with an inert/non-oxidising gas both prior to and simultaneously with the addition of the sulphoxy radical containing reagent.

8. A method as claimed in any one of the preceding claims wherein the slurry contains a mixture of valuable minerals including sulphidic copper minerals, sulphidic and non-sulphidic copper minerals, non-valuable sulphidic iron minerals and non- sulphidic gangue material.

9. A method as claimed in any one of the preceding claims wherein the slurry is produced from sedimentary copper deposits, copper skars, porphyry 10 copper/molybdenum/gold deposits or super gene enrichments.

A method as claimed in any one of the preceding claims wherein the duration and intensity of the inert/non-oxidising gas addition is controlled in conjunction with the amount and type of sulphoxy agent added and/or the dissolved oxygen content of the slurry. 15

11. A method as claimed in any one of the preceding claims wherein the method is applied to the rougher/scavenger flotation stage of the mineral separation circuit.

12. A method as claimed in any one of the preceding claims wherein the method is applied to the cleaning stage of the mineral separation circuit.

13. A method as claimed in any one of the preceding claims wherein after addition of the sulphoxy radical-containing reagent and inert/non-oxidising gas and prior to flotation, the slurry undergoes an oxidative gas conditioning to provide a dissolved oxygen concentration or electrochemical potential which is suitable for flotation of a particular sulphide mineral. -14-

14. A method of reducing the consumption of alkaline pH modifier and a mineral separation circuit employing a suiphoxy radical-containing reagent substantially as hereinbefore described with reference to any one of the accompan ying drawings. DATED this 8th Day of' July, 1998 BOG GASES AUSTRALIA LIMITED Attorney: PAUL G. HARRISON Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS V 0