AU7194198A

AU7194198A - Reagent consumption in mineral separation circuits

Info

Publication number: AU7194198A
Application number: AU71941/98A
Authority: AU
Inventors: Walter Hoecker; Andrew Newell
Original assignee: BOC Gases Australia Ltd
Current assignee: BOC Ltd Australia
Priority date: 1997-06-26
Filing date: 1998-06-17
Publication date: 1999-01-07
Anticipated expiration: 2018-06-17
Also published as: AU750843B2

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE

SPECIFICATION

FOP NS.TANDAFD

PATENT

OIINA

L

Name of Applicant: BOG GA ISES AUSTRALIA LIMITED, A.C. N. 000 029 729

I

kctual Inventors: Andrew,.NEWELL and Walter

HOECKER

Address of Service: BALDWIN SHELSTON

WATERS

60 MARGARET

STREET

SYDNEY NSW 2000 invention Title: "REAGENT CONSUMPTION IN MINERAL

SEPARATION

CIRCUITS'

Details of Associated provisional A pplication No. PO 7571 dated 26 June, 1997 The following statement is a full description of this invention, including the best method of performing it known to us:-- 7 -2- TECHNICAL FIELD This invention relations to a method of reducing both reagent consumption and scale formation in a mineral separation circuit employing sulphoxy compounds as reagents.

BACKGROUND TO THE INVENTION In the flotation separation of minerals, reagents from the sulphoxy group, such as i sodium sulphite, sodium bisulphite and sodium metabisulphite (or alkali metal or alkaline earth metal equivalents), sulphur dioxide or other thionates are used to improve the quality of the separation, particularly where sulphidic minerals such as chalcopyrite, S' 10 pentlandite, pyrite, sphalerite, pyrrhotite or galena are present.

These reagents may be effective per se but, unfortunately, the sulphoxy group reagents are susceptible to oxidation and need to be continuously replenished during the mineral separation process to maintain their efficiency and thus the quality of the Sseparation.

15 Oxidation may be caused by the presence of dissolved oxygen in water used within the mineral separation circuit which reacts with the sulphoxy compound to ultimately produce sulphate anions. Because such side reactions of dissolved oxygen and sulphoxy compounds result in consumption of sulphoxy compounds, increased dosage levels of sulphoxy compounds are required. Such consumption is endured by many flotation operations, which incur a major cost. In some cases, the costs may exceed 25% of the milling costs.

Further, water present within the mineral separation circuit usually contains high levels of cations such as calcium and magnesium which can react with the sulphate i. anions. The result is a degree of side-reaction which creates production of significant quantities of precipitate or scale (often gypsum (calcium sulphate)). This scale builds up on the internal surfaces of processing equipment, notably pH control and level control probes and discharge sections. It goes without saying that such problems interfere with the effective control of the mineral separation process and extended maintenance periods are required for scale removal. Needless to say, both can have detrimental economic consequences.

:i i; Additionally, the supply of such sulphoxy compounds, generally as solids, to remotely located flotation plant sites, as well as storage and preparation for use result in costs which have significant effects on the economics and productivity of such sites.

The present invention seeks to overcome at least some of the problems of the prior art or at least provide a commercial alternative to the prior art.

SUMMARY OF THE INVENTION In a broad aspect, the present invention provides a method of reducing both the 15 consumption rates of sulphoxy compounds and scale formation in a mineral separation circuit employing a sulphoxy radical containing reagent wherein the sulphoxy radical .I containing reagent is introduced to the mineral separation circuit in combination with the introduction of a non-oxidising gas to reduce the degree of oxidation of said sulphoxy Sradical.

Suitable sulphoxy radicals include bisulphite and sulphite compounds, for example alkali metal salts containing these radicals. Sulphur dioxide may also be employed for this purpose.

-4- The non-oxidising gas is conveniently to be selected from the group consisting of inert gases and carbon dioxide and sulphur dioxide. Of the inert gases, nitrogen is most preferred for cost reasons but other inert gases such as argon may also be used.

The non-oxidising gas is introduced preferably during any or all of the reagent conditioning and flotation stages, the stages where the presence of dissolved oxygen in a slurry passing through these stages is most likely to create the conditions conducive to oxidation of sulphoxy radicals and the scale formation and reagent consumption problems described above. However, the non-oxidising gas may also be introduced during the milling stages with beneficial results.

10 The rate of addition of the non-oxidising gas should be at a rate that reduces oxygen levels below those likely to result in sulphation, that is oxidation, of the sulphoxy radicals introduced by usage of sulphoxy racial containing reagents in the -a mineral separation circuit. Addition rate of the non-oxidising gas may consequently be controlled having reference to sensed values of dissolved oxygen levels or electrochemical potential in slurries within the milling, conditioning or flotation stages :of a mineral separation plant. In this way, feedback control over the rate of addition of the non-oxidising gas may be achieved. Suitable dissolved oxygen and electrochemical potential sensors are known from use in chemical processes and thus further description is not provided herein.

Although the above description implies the use of a single non-oxidising gas, this is not mandated by the present invention and mixtures of non-oxidising gases such as those described above may be used as desired.

The non-oxidising gas as mentioned hereinabove may be used to replace a portion of the air in, for example, flotation cells or columns. Therefore, existing equipment used for gas/liquid contact in the mineral separation circuit will be equally applicable in a circuit using the method of the invention.

Alternatively, the non-oxidising gas may be sparged into a slurry prior to flotation in, for example, conditioning or other tanks or even-the pipelines used to convey mineral separation circuit slurries from one stage of the process to another.

As the method of the invention is applicable to any mineral separation circuit S: utilising sulphoxy radical containing reagents, usually as depressants, a detailed 1o description of the arrangement and operation of such mineral separation circuits is readily accessible and apparent to those skilled in the art and is therefore not necessary and not provided herein- BEST MODE(S) FOR CARRYING OUT THE INVENTION S" In order that the nature of the present invention may be more clearly understood, 15 the following examples are provided.

Flotation tests were conducted on two samples of reagentised flotation slurry from a complex massive sulphide copper lead zinc ore to establish the reduction in sulphoxy compound consumption possible by addition with nitrogen. The valuable Si minerals present included chalcopyrite (Copper), galena (Lead), and sphalerite (Zinc).

The major non-valuable sulphide mineral was pyrite.

In the examples given, the intended role of the sulphoxy compound was to improve the flotation selectivity of the copper minerals from the lead and zinc minerals.

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r iL i- w r r 3 -6- Sample 1 Two tests were conducted on a fresh sample of reagentised flotation plant feed slurry assaying assaying 1.1% Copper, 2.7% Lead, and 8.3% Zinc.

Test 1: Standard Conditions The slurry was fed to a 2.5 litre laboratory flotation cell and floated according to the following operations and reagent additions: Conditioning 1 1350 Reagent addition 2 Conditioning with air 1 Reagent addition 900 Flotation Concentrate 1 1 Reagent addition 450 Flotation Concentrate 2 2 Flotation Concentrate 3 2 Sodium Meta Bi Sulphite (SMBS) was the sulphoxy type compound. The collector to was approximately 60 percent Isopropyl Ethyl Thiocarbamate and 40 percent Sodium Di Iso Butyl Di Thio Phosphate. The frother which was already present was Methyl Iso Butyl Carbinol.

The three concentrates and flotation tailings were filtered, dried, weighed, and the copper, lead, and zinc contents determined by assay.

Test 2: Combined Addition of Sulphoxy Compound with Inert Gas A test was conducted in a similar manner described for Test 1 with the following exceptions:

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1. The slurry was conditioned with a nitrogen gas purge of sufficient flow immediately prior to SMBS additions until the dissolved oxygen content of the slurry as measured with an appropriate sensor indicated essentially no dissolved oxygen present and during SMBS additions to maintain essentially no dissolved oxygen present.

2. Each of the SMBS addition rates.were reduced to 67 percent of the standard addition rates.

The total addition rate of SMBS was 1810 gpt versus the standard requirement of 2700 gpt S. :Sample 2 10 Two tests were conducted on a second sample of reagentised flotation plant feed slurry assaying assaying 1.1% Copper, 2.7% Lead, and 7.8% Zinc.

Test 3: Standard Conditions A test was conducted in a similar manner described for Test I Test 4: Combined Addition of Sulphoxv Compound with Inert Gas 15 A test was conducted in a similar manner described for Test I with the following exceptions: 1. The slurry was conditioned with a nitrogen gas purge of sufficient flow immediately prior to SMBS additions until the dissolved oxygen content of the slurry as measured with an appropriate sensor indicated essentially no dissolved oxygen present and during SMBS additions to maintain essentially no dissolved oxygen present.

2. Each of the SMBS addition rates were reduced to 50 percent of the standard addition rates.

The total addition rate of S',MS was 1350 gpt versus the stadaid requirement of 2700 gpt Results The results of the evaluation are summuarised as follows: Test 1: StAndard Conditions Product Concentrate Copper I Flotation Recoverv. Grade. Cu I Pb Zn I Cu Pb Zn Concentrate 1 16-4 I 4.7 5.3 177.6 8.4 3.1 Concentrates 1 13.5 6.8 2 890 1. 0 Conce-ntrates 1 1-6 6.6 7-1 91.4 1 19.6 6.9 In Test 2: Combined Addition Test 3: Standard Conditions -9- Test 4: Combined Addition SProduct Concentrate Copper Grade, Flotation Recovery i Cu Pb Zn Cu Pb Zn Concentrate 1 l3_7 4.5 5.8 I86.1 11.8 5.3 SConcentrates 1 12.0 5.5 6.6 91.8 17.7 7.

+2 SConcentrates I 6.0 7.1 92.8 20.9 8.6 +2+3 Comparing the results of Test I with Test 2 and Test 3 with Test 4 it is apparent that the addition of nitrogen permitted essentially identical metallurgical performance at significantly lower SMBS additions as measured by concentrate copper grade, copper flotation recovery, and flotation selectivity of copper against lead and zinc.

For some of these measures, this is probably more clearly appreciated on review of to the following figures in which:- Figure 1 is a graph showing the copper concentrate grade versus copper flotation recovery, for tests 1 and 2, Figure 2 is a graph of copper concentrate grade versus copper flotation recovery for tests 3 and 4, Figure 3 is a graph of copper flotation recovery versus lead flotation recovery for tests I and 2, and Figure 4 is a graph of copper flotation recovery versus lead flotation recovery for tests 3 and 4.

For this ore it is desirable to produce a copper concentrate of high copper grade.

Figures I and 2 clearly show that the addition of the inert gas, in this case, nitrogen in combination with the sulphoxy compound allowed similar concentrate copper grade and coper flotation recovery to be achieved at significantly lower addition rates of sulphoxy compound.

It is also desirable to separate copper from lead, therefore giving the highest copper flotation recovery while maintaining the lowest lead flotation recovery. Figures 3 and 4 once again show that the combined addition of the inert gas with the sulphoxy radical I containing reagent has given the required flotation selectivity of copper against lead but at-significantly lower addition rates of sulphoxy compound.

The use of inert gases such as nitrogen to allow significantly lower addition rates (consumptions) of sulphoxy compounds may allow the application of the process to a to wider range of ores and mineral separations than previously thought possible.

A reduction in scale formation is expected to come about by the reduction in sulphoxy compounds addition and that the addition of the inert gas excludes oxygen during sulphoxy compound conditioning. The inert gas purge may also be removing dissolved carbon dioxide that would otherwise form calcium carbonate scale.

Scale formation is undesirable from two points of view, build up on the processing equipment and also deposition on valuable mineral surfaces reducing their floatability.

The present invention is suitable for a wide range of ores including but not limited to ores with valuable suiphidic copper minerals, sulphidic and non-sulphidic copper minerals, non-valuable sulphidic iron minerals and non-sulphidic gangue materials. It is also suitable for use with sedimentary copper deposits, copper skarns, porphyry copper/molybdenum/gold deposits or super gene enrichments.

While the examples show reductions in the consumption of sulphoxy reagents m the order of several kilograms per tonne of ore treated, the present inventive process is q -I also suitable in instances where reduction in the consumption of the sulphoxy reagent may only be a few hundred grams per tonne.

It will be appreciated that the method described may be embodied in other forms without departing from the spirit or scope of the invention as defined by the attached claims.

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Claims

1. A method of reducing both the consumption rates of sulphoxy compounds in a mineral separation circuit employing the sulphoxy radical containing reagent wherein said sulphoxy radical containing reagent is introduced to a slurry in the mineral separation circuit in combination with the introduction of a non-oxidising gas to reduce the degree of oxidation of said sulphoxy radical.

2. A method as claimed in claim 1 wherein the sulphoxy radicals include bisulphite and sulphite compounds, alkali metal salts containing these radicals or sulphur dioxide.

3. A method as claimed in any one of the preceding claims wherein the non-oxidising to gas is selected from the group consisting of inert gases, carbon dioxide and sulphur dioxide.

4. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is nitrogen.

5. A method as claimed in any one of the preceding claims wherein a sulphoxy radical containing reagent is selected from the group consisting of sodium sulphite, sodium hydrogen sulphite, sodium metbisulphite, sodium bisulphite, sulphur dioxide gas or solution, sulphite agents and K, Ca, NH4 salt thereof, and admixtures thereof.

6. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is introduced into the slurry during any or all of the reagent conditioning and flotation stages.

7. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is introduced into the slurry immediately before introduction of the sulphoxy radical. r A. f ii r: r- II~ U.13-

8. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is introduced during the milling stage.

9. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is added to the slurry at a rate that reduces oxygen levels below that likely to result in I 5 sulphation/oxidation of the sulphoxy radicals. A method as claimed in claim 8 wherein the rate of addition of the non-oxidising gas is controlled by reference to sensed values of dissolved oxygen levels or S electrochemical potential in slurries within the milling, conditioning or flotation stages o of a mineral separation plant.

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11. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is sparged into the slurry prior to flotation in the conditioning tank or in the pipelines used to convey the slurry from one stage of the mineral separation process to another.

12. A method as claimed in any one of the preceding claims wherein at least a portion I. of the flotation gas used in the flotation cell comprises one or more of the non-oxidising 15 gases.

13. A method as claimed in any one of the preceding claims wherein the non-oxidising gas is introduced into the slurry in a quantity sufficient to reduce scale formation in the S mineral separation circuits.

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

A method as claimed in any one of the preceding claims wherein the slurry Scontains a mixture of valuable minerals including sulphidic copper minerals, sulphidic I g -14- and non-sulphidic copper minerals, non-valuable sulphidic iron minerals and non- sulphidic gangue material.

16. A method of reducing both the consumption rates of sulphoxy compounds and scale formation in a mineral separation circuit employing the sulphoxy radical containing reagent substantially as hereinbefore described with reference to any one of the examples and drawings but excluding comparatives. DATED this 17th Day of June, 1998 SBOC GASES AUSTRALIA LIMITED Attorney: IAN T ERNST Fellow Institute of Patent Attorneys of Australia of BALDWIN SHELSTON WATERS aca o i?