WO1992013640A1

WO1992013640A1 - Method of treating a base metal bearing material

Info

Publication number: WO1992013640A1
Application number: PCT/AU1992/000043
Authority: WO
Inventors: Murray Stanley Barnham; Phillip Darcy Owen; Ian Grant Pattison
Original assignee: Denehurst Limited
Priority date: 1991-02-06
Filing date: 1992-02-06
Publication date: 1992-08-20
Also published as: CA2101517A1; MX9200479A; PT100091A; YU11692A

Abstract

The invention relates to a method of treating a base metal bearing material for recovering a metal concentrate, by conditioning the base metal bearing concentrate with a slurry having a pulp density of at least 20 % solids in the presence of water whilst maintaining the slurry at a pH of at least 7 for a predetermined period of time and thereafter recovering the metal concentrate.

Description

METHOD OF TREATING A BASE METAL BEARING MATERIAL

Field of the Invention

The invention relates to a method of treating a base metal bearing material for recovering a metal concentrate . Typically this method is applied to treat a base metal tailing.

Background of the Invention

Whilst the following description of the invention is with reference to treatment of a tailing, the invention is not so limited.

Typically a base metal tailing is produced from mineral dressing operations located on an ore site. Such a tailing may contain commercially significant amounts of base metals, such as copper, lead, zinc and nickel. In these cases , mine operators have wanted to recover these base metals from the tailing in an economically viable way. In this case a tailing is recovered such as by dredging or sluicing and then is subjected to a concentrntion process, which may include flotation and/or other techniques such as gravity, to produce base metal concentrates . These tailing flotation processes can, although not exclusively, be applied to the concentration of zinc sulphide minerals from a tailing.

However, minerals in a tailing dam generally respond only poorly to a flotation process . This is due to the chemical environment in which they have been stored subsequent to their previous treatment. Furthermore, because of their generally low grade a high xipgrade ratio is required to achieve a saleable concentrate .

Consequently, flotation treatments of such a tailing have had only limited success in producing reliable and saleable base metal concentrates . Summary of Embodiments of the Invention

Accordingly, investigations have been directed to the effects of changes to the conditioning of the base metal bearing material and to the flotation conditions of the subsequent treatment.

Surprisingly, it has been found that improvements in the level of recovery of base metal concentrate coupled with low pyrite recovery during the flotation step can be achieved by subjecting the base metal bearing material (e. g. tailing) to a particular conditioning treatment. This can result in substantial upgrading of feed values.

More particularly, there is provided a method of conditioning a base metal bearing material for subsequent recovery of base metal concentrate comprises forming a slurry having a pulp density of at least 20% solids by the addition of water to the base metal material, and maintaining the slurry at a pH of at least 7 for a predetermined period of time. If necessary the pH may be maintained at the desired pH by addition of alkali (e.g. lime or caustic soda) .

Preferably the base metal is copper, lead, zinc and/or nickel.

The pH of the slurry is maintained in the preferred range of 7.0 to 8.5.

The preferred range of pulp density of the slurry is from 30-60% solids.

The preferred predetermined period of conditioning time is about 1 hour or more and more preferably from about 1 hour to about 2 hours .

To optimise the conditioning of the surface of the base metal material it is desirable to agitate the slurry. In one preferred form of the invention the conditioning treatment comprises forming a slurry having a pulp density of at least 20% solids by the addition of water to the base metal bearing material and maintaining that slurry at a pH of at least 7 for a period of greater than about 1 hour whilst agitating the slurry. The regulation of a minimum pulp density and preferably agitation of the slurry has found to allow conditioning times less than that previously expected. The higher the pulp density or the more intense the agitation the shorter the conditioning times .

The agitation may be by any suitable means . However, preferably the means imparts shear to the slurry whilst maintaining the slurry in suspension .

Typically, where the base metal bearing material is a tailing it may include sphalerite, pyrite and other base metal sulphide minerals mixed with non-sulphide gangue materials (e . g. talc, chlorite and quartz) .

Investigations have also found that the temperature of the slurry has little effect on the conditioning step though elevated temperature may subsequently affect the flotation reagents. Similarly during this conditioning there is no need to add the flotation reagents . However, pH modifiers may be added. In fact it is preferable that those reactants (other than pH modifiers) are added after the conditioning stage.

The refinement in operating practice of the process of the invention has potentially important commercial implications for enhanced profitability and reliability of recovery . The conditioning has facilitated reliable, repeatable recoveries of base metal concentrate .

According to another preferred form of this invention there is also provided a method of producing a base metal concentrate from a base metal bearing tailing which comprises :

(a) recovering a base metal bearing tailing and placing it in one or more vessels;

(b) adding water to the tailing to form a slurry having a density of at least 20% solids ;

(c) maintaining the slurry at a pH of at least 7 for a period of about 1 hour or more; (d) adding at least one flotation reagent to the slurry;

(e) subjecting the slurry to flotation to recover the base metal concentrate ; and (f) dewatering (e. g. thickening and filtering) the base metal concentrate .

(a) recovering a base metal tailing and placing it in one or more vessels;

(b) adding water which has a pH of at least 5 to the tailing to provide a slurry having a density of at least 20%; (c) agitating the slurry whilst maintaining the slurry at a pH of at least 7 for a period of up to about 2 hours;

(d) adding at least one flotation reagent to the slurry;

(e) subjecting the slurry to flotation to produce the base metal concentrate; and (f) dewatering the base metal concentrate.

When necessary the water has been treated to maintain the pH by the addition of alkali reagents such as caustic soda or lime.

Preferably a number of holding vessels are used to provide a surge capacity to ensure continuous supply and the necessary conditioning for successful subsequent flotation.

Generally, flotation will take place in a number of stages (e. g. four) , comprising a rougher stage followed by a number of cleaning stages (e.g. three) . After the final cleaning stage the base metal zinc concentrate is de-watered .

Preferably, flotation reagents are used after the slurry has been preconditioned to render the desired mineral selectively amenable to the flotation process. The reagent addition is tailored to suit the mineral or minerals from which it is desired to recover the base metal.

In the case of recovery of zinc bearing material, a number of reagents have been found to be preferable . The reagents added can be classified into three groups, namely : (1) activators (such as CuSO .) ;

(2) depressants (such as sodium metabisulphite (MBS)) ; and

(3) collectors (such as potassium amyl xanthate (PAX) , sodium isobutyl xanthate (SIBX) or a dithiophosphate thioncarbamate formulation (e. g. AERO 4037)) .

The reagents used in the rougher stage are typically either CuSO . , MBS , an alkali and SIBX or CuSO₄, SBS , an alkali and SIBX. A preferred reagent composition for the flotation is 1000 g/t MBS, 500 g/t CuSO₄, 100 g/t SIBX at a pH of between 9 and 9.5.

The reagents used in the first and second cleaning stages are typically alkali and SIBX, preferably in the following amounts : 300 g/t NaOH and 0-10 g/t SIBX.

In the first cleaning stage the pH of the slurry is preferably 10 to 11.5 and more preferably 10.2 to 10.4, whereas in the second cleaning stage the pH is preferably 11 to 12.

The third cleaning stage generally uses an alkali, typically at an addition rate sufficient to give a pH of least 11.0.

By way of example, the slurry density to the roughing stage should be about 25% - 40% solids and the slurry density in the cleaning stages should be in the range of about 20% - 50% solids and preferably 20 - 35% solids .

The tailing from the rougher stage may be pumped directly back to a disposal site. The water may be recovered for re-use .

It is far from clear why conditioning according to the invention causes the significant improvement in the recovery of base metal concentrate . However, it is thought to arise from an attrition which results in cleaner particle surfaces and/or some disaggregation of the particles which increases the liberation of minerals . In either case the particles are rendered more suseptible to subsequent flotation techiques. 6.

Brief Description of the Drawings

The invention is now further illustrated with reference to the accompanying drawings and examples in which :

FIGURE 1 shows graphically a Zn grade versus Zn recovery curve for the roughening stage for a tailing which was conditioned and one which was unconditioned in early test work.

FIGURE 2 shows graphically a Zn recovery versus Zn grade curve for the process of this invention.

FIGURE 3 is a flow chart of the floation circuit used in the subsequent investigation of the process of the invention.

FIGURE 4 shows graphically a Zn grade versus Zn recovery curve for a series of samples under differing conditioning conditions.

In preliminary investigations the first attempt to recover Zn from a tailing was a two stage process where the tailing was aerated in a slurry and then a bulk concentrate was floated from the slurry. The conditions for the aeration stage (2 - 6 hours) were 40% solids mixed in a pH 3 solution that contained a minimum quantity of copper (approximately 3 - 500 ppm Cu) . Under these conditions up to 20% of the contained zinc (10 - 20 g/1 Zn) was leached and the structure of the particles was modified. Aeration was followed by flotation at the natural pH of the aeration solution using a fatty acid flotation reagent. A bulk zinc/lead concentrate was produced .

When these parameters were carried out on a tailing from Woodlawn Mines, New South Wales, Australia, the results were not reproduced . The process was then modified to float a low grade zinc concentrate (8 - 10% zinc at 80% recovery) using pH 3 water contaminated with metal ions . The flotation step also recovered the pyrite from the tailing. While the process was being defined in a pilot plant, a flotation concentrate was produced which floated less pyrite and contained a high grade zinc rougher concentrate with low weight recovery - typically 40% zinc at 40% recovery.

The flotation conditions were :

1000 g/t MBS 500 g/t CuSO₄ 75 g/t PAX pH 7.0 - 7.5 using tap water

Laboratory tests were then conducted to identify the conditions for achieving these results . The same reagent regime in the laboratory did not give the same results as those from the Pilot Plant, i.e . substantially more pyrite was recovered in the concentrate.

The Pilot Plant practice was then investigated . The procedure for mixing a batch of tailing for feed was recognised as a major variation. There was a delay of at least 2 hours between when the slurry was prepared and the flotation test carried out.

This procedure was simulated in the laboratory by conditioning the slurry sample in the float cell for 2 hours prior to flotation with water a pH 5-7. Similar results to those for the Pilot Plant resulted. An example of the results showing this conditioning effect is shown in Figure 1.

A flotation reagent scheme of :

1000 g/t MBS 500 g/t CuSO^

75 g/t PAX pH 7.0 - 7.5

was used. 8.

However, this conditioning effect was found to be variable with the procedure being unsuccessful in some sample locations.

The variables which were investigated included time, temperature and pulp density. Included in this work was the optimisation of the flotation reagents .

Temperature

Initial indications were that by increasing the temperature the conditioning time could be decreased . This did not prove to be the case during these tests and a conditioning temperature of 20 to 40°C was best. The effect of temperature is shown in Table 1.

Table 1 - Variation of Results with Conditioning Temperature

TEMPERATURE ZINC CONCENTRATE GRADE ZINC RECOVERY °C % %

20 30 15.4 62

40 14.1 65

60 3.4 33

80 1.8 6

At the high temperatures (+40°C) the flotation reagents were destroyed .

Time

A minimum conditioning time of about 2 hours was established and the variation with conditioning time is shown in Table 2. Table 2 - Variation of results with Conditioning Time

TIME HRS ZINC CONCENTRATE GRADE ZINC RECOVERY

% %

69 49

74 75

Tests showed that there was no variation in float results when the pulp density during conditioning was varied between 30 - 60% solids .

Flotation Reagents

A series of reagents for flotation were evaluated . The end result was the choice of PAX and Cyana id Aero 4037 for the flotation.

Results were still variable depending on sample location. Testwork to date had been restricted to near surface samples.

At this point, +/-30% engineering estimate was carried out for the processing of 3 million tonnes of tailing.

E__

At this stage the pH regime was increased to a pH of 9-9.5.

The design basis for the flotation was defined as :

1000 g/t MBS

500 g/t CuS0₄

50 g/t PAX

50 g/t 4037 pH 9.0 - 9.5 10.

In conjunction with this study a core sampling programme of the tailing dam at Woodlawn Mines was completed and the preconditioning and flotation conditions were tested on core sections .

The previous variability in results with location was not present. Analysis of the results indicated this may have been due to the fact that the natural pH of the slurry was always greater than 7.

Also during the 2 hour conditioning period the pH remained above 7.

The importance of maintaining the pH of at least 7 during the conditioning period was then confirmed when it was shown that samples that had not previously responded to the technique did so when the slurry pH was adjusted to above 7 by addition of lime for the conditioning period.

Zinc rougher recoveries for the core samples averaged 83 - 85% compared to previous 75%. Feed grade varied between 2 - 7% Zn.

The flotation sequence was defined as :

Conditioning 2 hours pH >7.0

Flotation 1000 g/t MBS

500 g/t CuS0₄ 50 g/t PAX

50 g/t 4037 pH 9 - 9.5

The +/-30% study indicated that the project should proceed to more detailed evaluation. In particular flotation conditions were addressed .

Previous MBS, CuSO . and pH levels were found to be satisfactory. The combined collector of PAX and 4037 was found to be unsatisfactory during locked cycle testwork . The collector was changed to SIBX only 11.

which corrected this and gave the additional benefit of using one collector site wide.

The alkali used for pH modification was also varied with lime and caustic soda being investigated . Each gave similar results .

The conditions for upgrading the tailing were defined as :

Conditioning 2 hours - minimum pH > 7.0

Flotation 1000 g/t MBS

500 g/t CuS0₄ 100 g/t SIBX pH 9 - 9.5

Extended conditioning times for a period up to 24 hours have also been investigated and with no real change occurring after 2 hours .

Typical results using these conditions on the tailing are a rougher concentrate grade of 20 - 25% zinc at a zinc recovery of 80 - 85% in 10% of the weight. Typical iron recovery into the rougher concentrate is around 10%. Cleaning gives a final concentrate of 47% zinc at 61% recovery .

The optimised Zn recovery for a sample with average composition of the dam is shown in Figure 2. These results were attained with an average conditioning time of 1 hour or more .

Further investigations took place to reduce the conditioning times whilst at least maintaining recovery integrity .

A slurry was formed by introducing tailings and water from the Woodlawn Mine into two large holding tanks . Each tank held the slurry for approximately 10 hours . These tanks were filled during the day and continuously operated . The feed flowed through these tanks and into the conditioning plant . The slurry in the holding tanks was 12.

subjected to continuous mild agitation to ensure a slurry of predictable pulp density was delivered to the conditioning plant.

In the conditioning plant, the slurry was held for approximately 1 hour at a pH of about 7.7. During this time the slurry had a pulp density of approximately 35%. The slurry was also agitated during this period by an agitator capable of imparting high intensity shear to the slurry. Details of the agitator were as follows :

Type of Agitator Twin Level Axial Flow/Radial

Turbine Agitator Speed 6.2 m/s

Impeller Power Number (Np) 0.37 Axial Flow

5.0 Radial Turbine

Impeller Pumping Number (Nq) 0.62 Axial Flow

0.72 Radial Turbine Installed Power/ Unit Volume 2.2 kw/m³ Torque/Unit Volume 206 Nm/m³ Ratio Impeller Diameter/ Tank Diameter 1.2m/4.25m = 0.28

The conditioned slurry was then subjected to a flotation circuit under the following conditions :

Flotation 600 g/t SO₂ added SBS or MBS 500 g/t CuS0₄ 100 g/t SIBX pH 9 - 9.5

The flotation circuit was in several separate stages . Each stage began with a feed which was separated into a concentrate and a tail . A rougher stage was initially produced followed by three cleaning stages . Feed for the rougher stage was from the conditioning plant and product from each stage provided the feed for each succeeding stage and the tail returned to each preceding stage . The circuit is illustrated in Figure 3. 13.

The results of the testing are shown in Figure 4. Figure 4 shows graphically Zn grade versus Zn recovery curves for the samples . In particular the four different samples tested were as follows :

TA-201 SAMPLE - This sample did not undergo any conditioning prior to flotation.

TA-201 SAMPLE - This sample underwent conditioning for 60 minutes in a laboratory flotation cell.

TA-201 SAMPLE - This sample underwent conditioning for 60 minutes whilst being agitated with an agitator having a speed of 3.8 m/s . The agitator was a laboratory scale twin level axial flow/radial turbine.

TA-2O1 SAMPLE - This sample underwent conditioning for 60 minutes whilst being agitated with the same agitator but having a speed of 6.4 m/s

These examples showed that conditioning for times below 2 hours, in particular about 1 hour, whilst imparting agitation to a slurry, improved flotation recovery of a base metal from the base metal bearing material.

Accordingly by selecting a particular pH range and minimum residence time it is possible to improve flotation recovery of a base metal from a base metal bearing material .

Claims

14.THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS :

1. A method of conditioning a base metal bearing material for subsequent production of a base metal concentrate comprises forming a slurry having a pulp density of at least 20% solids by the addition water to the base bearing metal material, and maintaining the slurry at a pH of at least 7 for a predetermined period of time .

2. A method of conditioning according to claim 1 wherein the pH of the slurry is maintained by the addition of alkali.

3. A method of conditioning according to either claims 1 or 2 wherein the slurry is maintained at a pH in the range of 7.0 to 8.5.

4. A method of conditioning according to any one of claims 1 to 3 wherein the pulp density of the slurry is from at least 30% solids.

5. A method of conditioning according to any one of claims 1 to 3 wherein the pulp density of the slurry is from 30 - 60% solids.

6. A method of conditioning according to any one of claims 1 to 5 wherein the predetermined period of time is about 1 hour or more.

7. A method of conditioning according to any one of claims 1 to 5 wherein the predetermined period of time is from about 1 hour to about 2 hours.

8. A method of conditioning a base metal bearing material for subsequent production of a base metal concentrate comprises forming a slurry having a pulp density of at least 20% solids by the addition of water to the base metal bearing material and maintaining that slurry at a pH of at least 7 for a period of greater than about 1 hour whilst agitating the slurry.

9. A method of conditioning according to claim 8 wherein the agitation imparts shear to the slurry whilst maintaining the slurry in suspension . 15.

10. A method of conditioning according to any one of claims 1 to 9 wherein the tailing includes sphalerite , pyrite and other base metal sulphide minerals mixed with non-sulphide gangue materials .

11. A method of producing a base metal concentrate from a base metal bearing tailing which comprises :

(b) adding water to the tailing to form a slurry having a pulp density of at least 20% solids ;

(c) maintaining the slurry at a pH of at least 7 for a period of about 1 hour or more;

(d) adding at least one flotation reagent to the slurry;

(e) subjecting the slurry to flotation to recover the base metal concentrate; and

(f) dewatering the base metal concentrate.

12. A method of producing a base metal concentrate from a base metal bearing tailing which comprises :

(a) recovering a base metal tailing and placing it in one or more vessels;

(b) adding water which has a pH of at least 5 to the tailing to provide a slurry having a pulp density of at least 20% solids;

(c) agitating the slurry whilst maintaining the slurry at a pH of at least 7 for a period of up to about 2 hours; (d) adding at least one flotation reagent to the slurry;

(e) subjecting the slurry to flotation to produce the base metal concentrate ; and

(f) dewatering the base metal concentrate .

13. A method of producing a base metal concentrate from a base metal bearing tailing according to either claims 11 or 12 wherein in step

(b) the slurry has a pulp density of at least 30% solids . 16.

14. A method of producing a base metal concentrate from a base metal bearing tailing according to either claims 11 or 12 wherein the pH of the slurry is maintained by addition of alkali.

15. A method of producing a base metal concentrate from a base metal bearing tailing according to either claims 11 or 12 wherein the at least one flotation reagent may is added after step (c) .

16. A method of producing a base metal concentrate from a base metal bearing tailing according to any one of claims 11 to 15 wherein the base metal is copper, lead, zinc or nickel.

17. A method of producing a zinc concentrate according to claim 16 wherein the flotation reagent is selected from the following three groups:

(1) activators including CuSO .;

(2) depressants including sodium metabisulphite (MBS) ; and

(3) collectors including potassium amyl xanthate (PAX) , sodium isobutyl xanthate (SIBX) or a dithiophosphate thioncarbamate formulation

(e.g. AERO 4037)) .

18. A method of producing a base metal concentrate from a base metal bearing tailing according to any one of claims 11 to 17 wherein the flotation reagent is 1000 g/t MBS , 500 g/t CuSO₄, 100 g/t SIBX at a pH of between 9 and 9.5.

19. A method of producing a base metal concentrate from a base metal bearing tailing according to either claims 11 or 12 wherein flotation occurs in a plurality of stages comprising a rougher stage followed by at least a first cleaning stage and a second cleaning stage .

20. A method of producing a base metal concentrate from a base metal bearing tailing according to claim 19 wherein the flotation reagent used in the rougher stage is either CuSO . , MBS , an alkali and SIBX or CuS0₄, SBS, an alkali and SIBX.

21. A method of producing a base metal concentrate from a base metal bearing tailing according to claim 19 wherein the flotation reagent 17.

used in the first cleaning stage and the second cleaning stage is an alkali and a collector respectively.

22. A method of producing a base metal concentrate from a base metal bearing tailing according to claim 19 wherein the first cleaning stage the pH of the slurry is between 10 to 11.5 , and in the second cleaning stage the pH is between 11 to 12.

23. A method of producing a base metal concentrate from a base metal bearing tailing according to claim 19 further comprising a third cleaning stage wherein the flotation reagent used is an alkali added at a rate sufficient to maintain a pH of at least 11.0.

24. A method of producing a base metal concentrate from a base metal bearing tailing according to claim 19 wherein the slurry density in the roughing stage is between about 25% - 40% solids and the slurry density in the cleaning stages is between about 20% - 50% solids .

25. A method of producing a base metal concentrate from a base metal bearing tailing according to any one of claims 19 to 24 wherein the tailing from the rougher stage is pumped directly back to a disposal site and water is recovered for re-use.