located 10 km west of Chillagoe in Far North Queensland. Both copper and gold ..... $200 000 additional revenue after freight and smelting charges have been ...
Appraisal of the Jameson F~otation Cell for Recovery of Cyanide Soluble Copper
s KITTEL 1 AND G J HARBORT2 ABSTRACT Jameson cell pilot plant trials were conducted in a number of areas in the Red Dome gold/copper flotation plant during 1991. The aim of testworlc was to reduce the amount of cyanide soluble copper reporting in tailing to the gold leach plant, and hence reduce cyanide consumption. A number of these tests were conducted in parallel with conventional flotation columns. Laboratory tests were conducted to simulate the perfonnance of the existing plant when compared with the addition of the Jameson cell allowing an extra sulphidising phase. This paper reviews the comparison of the Jameson cell and conventional columns in recovering cyanide soluble copper, while maximising copper concentrate grade. Key parameters that are investigated are residence times, air/pulp ratios, superficial gas recoveries and size by size recoveries. A brief comparison of performance of the Jameson cell and column in the controlled potential sulphidisation process is also presented. An estimation of the reduction in cyanide consumption is given.
INTRODUCTION TO RED DOME OPERATIONS Niugini Mining owns and operates the Red Dome Gold Mine, located 10 km west of Chillagoe in Far North Queensland. Both copper and gold are mined from the open pit deposit at a current rate of 1.1 mt p y, grading 3.0 g/t Au, 0.5 per cent Cu and 8 g/t Ag. Mining commenced in 1986 with the initial treatment for gold recovery from low copper oxide ore by heap leaching. Grinding, flotation and CIL plants were commissioned in mid-1989 to treat the high copper oxide and sulphide ore types located deeper in the pit. Ore is treated in campaigns: 1.
flotation only ore when the gold head grade is less than 1.7 g/tAu;
2.
flotation/CIL when the head grade is greater than 1.7 g/t Au; and
3.
CIL only when the cyanide soluble copper levels are less than 0.1 per cent CNSolCu.
Sulphide and oxide ore types are blended for all campaigns to maintain stable grinding conditions. Primary crushed ore (-150 mm) is stacked on a mill feed stockpile and fed into the SAG MilllBall Mill circuit at 130-140 tph. A pebble crusher has recently been installed in this circuit to crush -80 mm SAG Mill discharge. This circuit modification is required due to the higher proportions of the harder sulphide ore being mined at depth. Final ground product has a P80 of 45 I!m. A small gravity spiral plant removes coarse native copper recirculating through the cyclone/Ball mill circuit. The flotation plant consists of two stages of column flotation followed by two stages of scavenger flotation in conventional cells. Sulphide copper minerals (Chalcocite, Bomite) and native copper are recovered in the first column flotation stage. Tails from this stage are treated through the remaining column and
scavenger stages with sodium sulphide added to all of them to recover oxide copper minerals (Malachite, Cuprite). Slower floating sulphides and some native copper are also recovered here. A small cleaner column is used to reclean the secondary column concentrate; scavenger concentrate is cleaned then recleaned in conventionally agitated flotation cells. Current metallurgical perfonnance from the flotation plant is typically 35 per cent copper concentrate grade, 92 per cent cyanide soluble copper recovery (recoverable copper) and 75 per cent gold recovery. Flotation tail is thickened then pumped 1 km for treatment through a conventional CIL plant Total plant gold recovery (flotation and CIL) is 95.5 per cent Au.
JAMESON CELL OPERATING PRINCIPLE The Jameson cell was developed jointly by Mount Isa Mines and Professor G J Jameson of the University of Newcastle, (Jameson, 1988). The cell is divided into two main zones, one for contacting and the other for concentrate cleaning. Contacting takes place in the downcomer (Figure 1), where the feed slurry and air are intimately mixed. This is achieved by supplying a high pressure feed to the cell. This pressurised input provides the motive energy for mixing and is let down through an orifice plate into the downcomer. The resultant plunging jet of liquid shears and then entrains air, that is being naturally drawn. Froth produced is characterised by having a 60 per cent voidage and a mean particle size of approximately one-third that achieved in a conventional column. Due to a high mixing velocity and a large interfacial area, there is rapid contact and capture of the concentrate particles by the bubbles. In effect, with the high voidage fraction, pulp is a thin film surrounding the air bubbles. The Jameson cell can be said to have two recovery zones. The primary zone is within the downcomer where the intense particle air contact occurs. Residence time within the downcomer varies from two seconds to ten seconds depending on application. The secondary zone is within the flotation tank itself where recovery maintenance and some secondary recovery occurs. Residence times within the flotation tank vary from approximately 40 seconds for roughing applications to three minutes for cleaning applications. (Harbort, 1992). The flotation tank also acts as a disengagement vessel. The concentrate laden froth is discharged from the bottom of the downcomer where it enters the quiescent outer portion of the cell. As the froth rises it can be washed by a COlUlter-current flow of water supplied from the top of the cell. A high purity concentrate 15 collected and overflows the top weir lip. Tailings flow to the base of the cell from which they are discharged.
TESTWORK RESULTS. Testwork was conducted with a 500 mm diameter pilot Jameson cell, using a 100 mm downcomer. The cell has a rated capacity of 130 litres per minute and was operated at around 100 litres per minute for testwork. The test unit was supplied with two inserts
1. Red Dome Pty Ltd. 2. MIM Holdings Limited, 410 Ann Street, Brisbane Qld 4000.
ExtraclJve Metallurgy 01 Gold and Base Metals
Kalgoorlie, 26 - 28 October 1992
211
S KTITEL and G J HARBORT
Results of testwork are detailed in Figure 2 and Figure 3 and Table 1. From these it is evident that the Jameson cell produced a more favourable grade/recovery curve compared to the column. On average Jameson cell recoveries were five per cent higher for a given concentrate grade. Recoveries for cyanide soluble copper followed a similar trend to that of total copper.
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BENCH SCALE SIMULATION TESTWORK FOR THE ADDITIONAL SULPffiDISATION STAGE
11)
Retrofitting a Jameson cell into the plant would be simpler in the prefloat application thus allowing the existing prefloat to become the first sulphidising stage. Earlier work had revealed most of the copper not recovered to be fine (-38 ~m) malachite and native copper indicating a fourth sulphidising flotation state could have benefits. In order to determine the benefits that an additional flotation stage would provide, a series of laboratory tests were carried out. While the pilot plant was being fed with primary column feed both feed and tail samples were collected from the Jameson cell for refloating in the laboratory. The feed sample was subjected to fpur flotation stages ie a prefloat and three sulphidising stages to simulate the plant performance.
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Experience at Red Dome has shown that above a certain base level each extra 0.01 per cent CNSolCu in ClL feed increases the cyanide consumption by 0.3 kg/to The current flotation tail target is 0.06 per cent CNSolCu which produces a cyanide consumption of 1.4 kg/t (0.07 per cent CNSolCu = 1.7 kg/t CN consumed!). Milling throughput on some occasions has been reduced in order to maintain acceptable CNSolCu levels in the flotation tail. There have also been occasions when the ClL plant has been bypassed due to hi~h cyanide consumption rendering treatment uneconomic.
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ie Primary float -+ CPS 1 -+ CPS 2 -+ CPS 3 FIG 7 - Typical sulphidisation float.
A size recovery analysis showed recoveries for the Jameson cell to be similar to the column for the -38 micron fraction. The Jameson cell produced significantly better recoveries in the +38 micron material.
EFFECT OF CYANIDE SOLUBLE COPPER (CNSoICu) ON CYANIDATION Many copper minerals can be either totally or partially dissolved in cyanide solutions, the amount dissolved depending on the minerals present and their fineness. During the dissolution of copper, cyanide is consumed to form copper cyanogen complexes ranging from CuCN (a precipitate) through to CuCN43-. This complexed cyanide is then not available for gold leaching, (Chemistry of Cyanidation, 1968). Adequate free cyanide levels must be maintained to ensure that any copper present is fully complexed to CuCN4 3-, a state from which it will not be adsorbed onto carbon. Inadequate free
214
Tail sample, collected from the Jameson cell (which was duplicating the plant primary float) was refloated using four sulphidising stages. This simulated the Jameson cell in the prefloat application with the existing circuit all converted to sulphidising stages. Jameson Primary Float -+CPS 1 -+ CPS 2 -+ CPS 3 -+ CPS 4 Laboratory testing was carried out as soon as the sample was collected to minimise any effects from oxidisation or sample aging. No reagent was added to the prefloat tests as the sample was collected downstream of the plant reagent addition point. Sulphidising was achieved over a three-minute conditioning period by the controlled addition of sodium sulphide to maintain a fixed sulphide ion potential (Es) of -500 mY. Collector addition during the CPS stages followed, with a two-minute conditioning time. Some frother was added just prior to turning the air on. For tests were carried out to provide greater confidence in the result. Results of this exercise are shown in Table 1.
KEY POINTS 1.
Under optimum conditions in a laboratory flotation cell an extra stage of CPS flotation had the potential to lower
Kalgoorlie, 26·28 October 1992
Extractive Metallurgy 01 Gold and Base Metals
APPRAISAL OF THE JAMESON FLOTATION CELL
However, due to the decommissioning of the en.. plant in a few months time, any proposed installation would not provide this economic benefit to Red Dome.
TABLE 3
Test
Yield %
Description
Copper Grade %
cnSCu Grade %
Av
Prefloat + 3CPS Con
7.04
5.09
Tests
Prefloat + 3CPS Tail
92.96
0.15
4.51 0.Q7
1-4
Prefloat + 3CPS Head
100.00
0.51
0.39
Jam Tail + 4CPS Con
7.27
2.68
2.41
Jam Tail + 4CPS Tail
92.73
0.14
0.04
100.00
0.32
0.23
Jam Tail + 4CPS Head
2.
Improved copper recovery - again based on a .conservative 0.015 per cent additional CNSolCu reporting as concentrate this would provide an extra 165 tonnes of saleable coper per year. This represents over $200 000 additional revenue after freight and smelting charges have been deducted. As the copper head grade increases so does the potential for additional copper recovery with an additional flotation stage. The proposed Griffith Hill deposit which is adjacent to the main pit is primarily native copper grading up to four per cent Cu, a feed type highly suited to primary flotation. Additional flotation capaci~ may be required to allow this ore to be treated at the current milling rate of 140 tph. 3.
Higher gold recovery in flotation - with the imminent closure of the main pit the remaining feed stock (Griffith Hill and stockpiled oxide ore) is all flotation only (less than 1.7 g/t Au). Thus emphasis will be on maximising gold recovery in flotation. Although no gold assays were included in the pilot scale work, it is fair to assume that an additional flotation stage may result in increased gold recovery.
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CONCLUSION
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1.
Concentrate grades produced by the Jameson cell were consistently better than the primary or secondary columns. This was due to less gangue entrainment possibly as a result of: lower superficial air velocity in the Jameson cell; and some physical separation of clay from mineral in the downcomer.
2.
Recovery of the coarse mineral (+38 J.Ull) was better achieved by the Jameson cell (in comparison to columns). This was shown to be true for the primary and secondary applications.
3.
Laboratory testwork indicates an extra CPS stage could reduce cyanide soluble copper levels in the tail by as much as 300 ppm.
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FIG 8 - Sulphidisation flotation testwork.
the CNSCu by about 300 ppm. This was evident in three of four tests. 2.
3.
The ore in Test 4 was the most readily floatable revealing that a prefloat and three stages of CPS flotation were sufficient to optimise copper recovery. Additional copper would be recovered with another flotation stage in the order of 1.0 tpd (300 ppm x 3300 tpd).
BENEFITS OF AN ADDITIONAL FLOTATION STAGE AT RED DOME An additional flotation stage would provide one or more of the following advantages depending on the ore type being treated. 1.
Lower cyanide consumption - this testwork revealed that an additional stage of flotation had the potential to reduce To be CNSolCu in CIL feed by 0.03 per cent conservative a 0.015 per cent reduction in CNSolCu over a 12-month period would equate to a cyanide saving of around $840 000 based on a throughput of 1 100 000 tonnes.
Extractive Metallurgy of Gold and Base Melals
ACKNOWLEDGEMENTS The permission of MIM Holdings Ltd, Nuigini Mining and the management of the Red Dome gold mine to publish this paper is gratefully acknowledged.
REFERENCES Cyanamid, 1968. Chemistry of cyanidation, No 23 rev. Harbort G J, 1992. Jameson cell developments and applications, AMMTEC Flotalion Colloquium, May 27, Unpublished. Jameson G J, 1988. A new concept in flotation cell design. Co1wnn '88 Proceedings of an International Symposium on Column Flotation, Phoenix, Arizona, USA, pp 281-286. Jones M H, Kwan-Yu Wong, Woodcock J T, 1986. Controlled potential sulphidisation and rougher cleaner flotation of an oxide-sulphide copper ore, 13th CMMI Congress, Singapore, pp 33-43. Kiue1, S J, 1991. Jameson cell testwork, Red Dome Ply Ltd company report.
Kalgoorlie, 26 - 28 October 1992
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Extractive Metallurgy of Gold and Base Metals
