2.4m Thickener Preliminary Report Rev0

Sunrise Dam Gold Mine Paste Thickening R&D Programme

PASTE

Rev

Information witby parties othe

SUNRISE DAM GOLD MINE

2.4m PILOT THICKENER

THICKENING R&D PROGRAMME

PRELIMINARY REPORT

ision No. Proposed by Authorised by Date Issued

0 J. Amaranti GTS 7th July 2003

hin this report is commercial-in-confidence and as such must not be used or reproduced in any way r than Outokumpu Technology or Sunrise Dam Gold Mine


TABLE OF CONTENTS

1.0 Introduction 5

2.0 Summary 9

3.0 Testwork and Procedures 18

3.1 Sample Preparation 18 3.2 Thickener Mechanisms 19 3.3 Flocculant Addition 20 3.4 Measurements 20 3.5 Rotating Bed Determination 21 3.6 Rheology Measurements 22

4.0 Results 24

5.0 Conclusions and Recommendations 36

Appendix 1 38 Photographs 38

Appendix 2 39 Logsheets 39

Appendix 3 40 Procedures 40

Appendix 4 41 Lab Simulation of Underflow % Solids vs Unsheared Yield Stress 41

Information within this report is commercial-in-confidence and as such must not be used or reproduced in any way by parties other than Outokumpu Technology or Sunrise Dam Gold Mine


LIST OF FIGURES AND TABLES

Figure 1. SDGM 24m High Compression Thickener....................................................................................... 5 Figure 2. SDGM Central Tailings Discharge ................................................................................................... 7 Figure 3. General Arrangement of 2.4m Pilot Thickener ............................................................................... 8 Table 1. Best Operating Result ........................................................................................................................ 9 Figure 4. Comparison of 2.4m Pilot Thickener & 24m HCT Underflow Densities........................................ 10 Figure 5. Unsheared Yield Stress vs Underflow % Solids............................................................................. 10 Table 2. Effect of Centrifugal Pump on Yield Stress...................................................................................... 11 Table 3. Effect of Rheometer Shearing Events on Yield Stress .................................................................... 11 Table 4. Effect of Underflow Recirculation on Yield Stress........................................................................... 11 Figure 6. Operating Torque vs Unsheared Yield Stress ................................................................................ 12 Figure 7. Operating Torque vs Underflow % Solids....................................................................................... 12 Figure 8. k Factor vs Unsheared Yield Stress ............................................................................................... 13 Figure 9. k Factor vs Underflow % Solids....................................................................................................... 14 Figure 10. Underflow % Solids vs Flocculant Dosage ................................................................................... 14 Figure 11. Comparison 190mm Laboratory Pilot Rig & 2.4m Pilot Thickener.............................................. 15 Figure 12. 190mm Laboratory Pilot Rig........................................................................................................... 15 Figure 13. 2.4m Pilot Thickener ....................................................................................................................... 16 Table 5. 2.4m Thickener Testwork at Sunrise Dam Goldmine March – May 2003 ....................................... 17 Figure 14. 2.4m Pilot Thickener Arrangement ................................................................................................ 18 Figure 15. Feed Pump and Header Tank ......................................................................................................... 19 Figure 16. Pilot Thickener Rig.......................................................................................................................... 19 Figure 17. Rakes with 8 Stationary and 4 Rotating Pickets........................................................................... 19 Figure 18. Flocculant Dilution Setup ............................................................................................................... 20 Figure 19. Flocculant Manifold......................................................................................................................... 20 Figure 20. Observing Overflow Clarity ............................................................................................................ 21 Figure 21. Measuring U/F Flow Rate................................................................................................................ 21 Figure 22. Rotating Bed Detection................................................................................................................... 21 Figure 23. Slump Ring Test.............................................................................................................................. 22 Figure 24. Showing a Slump of Two Rings..................................................................................................... 22 Figure 25. Rheology Sample ............................................................................................................................ 23 Figure 26. Laboratory and Rheometer ............................................................................................................ 23 Figure 27. Illustration of Haake Yield Stress Printout.................................................................................... 23 Figure 28. Liquor SG Calibration Curve .......................................................................................................... 24 Figure 29. Hydrometer ...................................................................................................................................... 24 Figure 30. Comparison of 2.4m Pilot Thickener & 24m HCT Underflow Densities...................................... 26 Figure 31. Unsheared Yield Stress vs. Underflow % Solids.......................................................................... 27 Table 6. Effect of Centrifugal Pump on Yield Stress...................................................................................... 27 Table 7. Effect of Rheometer Shearing Events on Yield Stress .................................................................... 27 Figure 32. Illustration of Haake Yield Stress Printout.................................................................................... 28 Table 8. Effect of Underflow Recirculation on Yield Stress........................................................................... 28 Figure 33. Operating Torque vs Unsheared Yield Stress .............................................................................. 29 Figure 34. Operating Torque vs Underflow % Solids..................................................................................... 29 Figure 35. k Factor vs Unsheared Yield Stress ............................................................................................. 30 Figure 36. k Factor vs Underflow % Solids..................................................................................................... 31 Figure 37. Underflow % Solids vs Flocculant Dosage ................................................................................... 31 Table 9. Best Operating Result ........................................................................................................................ 32 Figure 38. 190mm Twisted Rotating and Static Pickets ................................................................................ 32 Figure 39. Comparison of 190mm Pilot Rig & 2.4m Pilot Thickener Run 1.................................................. 33 Figure 40. Comparison of 190mm Pilot Rig & 2.4m Pilot Thickener Run 2.................................................. 33 Figure 41. Comparison of 190mm Pilot Rig & 2.4m Pilot Thickener Run 3.................................................. 34 Table 10. 2.4m Thickener Testwork at Sunrise Dam Goldmine March – May 2003 ..................................... 35 Figure 42. Percent Solids vs Yield Stress....................................................................................................... 42



Acknowledgements

AngloGold Outokumpu Technology Pty Ltd would like to take this opportunity to thank AngloGold for this opportunity and its cooperation. Thank you to all AngloGold staff that were involved with the Paste Thickening R&D Programme. Installation of the 2.4m pilot thickener required a number of changes both electrically and mechanically. Outokumpu would like to express our appreciation for the services of the Electrical and Maintenance Departments at Sunrise Dam Gold Mine. Special thanks to the metallurgical team at Sunrise Dam Gold Mine in particular John McKenny, Drew Noble, Mike Di Trento and Nathan Marr for all their support and to all at Sunrise Dam Gold Mine. Outokumpu - Mineral Processing The Outokumpu Global Thickener Support Team would like to thank the following Outokumpu and associated personnel for their input, contributions and assistance; Outokumpu South Africa – Fred Bibbey, Francois Mouton, Mark Fowler and Schalk Bekker. McNally India – Pranab K Ghosh Outokumpu Eurasia – Vladimir Lasukov Outokumpu Australia – Warren Hinchliffe, Allan Webb, Craig Bonython, Brian Hartley, Phil Diesel, Grant Hankinson, Jay Benn and Jon Owen.



1.0 Introduction AngloGold’s Sunrise Dam Gold Mine (SDGM) is located 220km north northeast of Kalgoorlie and 55km south of Laverton, Western Australia, in semi arid bush. SDGM currently treats up to 450 t/h of ore and operates a Central Tailings Discharge (CTD) storage facility with thickened tailings being produced by a Supaflo 24m High Compression Thickener (HCT) Figure 1.

Figure 1. SDGM 24m High Compression Thickener

SDGM contacted Outokumpu Technology Pty Ltd (Outokumpu) in regard to lower than desired underflow density from their 24m HCT coupled with problematic thickener operation. Outokumpu perceived that the poor overall performance was due to the rheology of the material and it’s tendency to form a rotating bed when higher underflow densities were targeted. A Paste Thickening R&D Programme was agreed to and completed at SDGM based on an agreement between AngloGold and Outokumpu. Outokumpu initiated the design and construction of a 2.4m pilot thickener to be used in assessing the performance possibilities of the ore being treated. General Arrangement of the 2.4m pilot thickener, Figure 3, can be seen on page 8. The objective of this R&D programme was to provide process and/or mechanical solutions for the operation of the existing tailings thickener circuit. In a steady state thickening process, densification of the slurry can only proceed if the rate of water release from the slurry migrating upwards through the thickener is greater than the transport of the densified slurry migrating downwards.



The rate of water release is governed by the natural permeability of the slurry, and is enhanced by mechanical rake action. The 2.4m pilot thickener was able to be fitted with different rake mechanisms to confirm formation and then prevention of a rotating bed, as it was believed that the prevention of this would maintain permeability as well as maintain the usable area of the thickener. By increasing underflow density it will be possible to improve the CTD system, increase water recovery and effectively reduce reagent consumption, which leads to a number of environmental benefits and cost savings. The R&D programme consisted of the following:

• Testing different rake mechanisms for the verification and then prevention of a rotating bed

• Testing underflow density versus yield stress, torque and flocculant dosage • Testing side by side of Outokumpu’s 190mm laboratory pilot rig versus 2.4m

pilot thickener to compare results. The main objectives of the testwork were:

• To confirm that a rotating bed would be formed in the pilot thickener • To compare and optimise the relative effectiveness of different rake

configurations for rotating bed prevention • Determination of unsheared yield stress versus underflow percent solids • Determination of yield stress before and after centrifugal pump • Simulation of yield stress after pump using Haake Viscometer • Determination of yield stress after recycling of underflow • Determination of k factor (torque) versus unsheared yield stress

• Determination of k factor (torque) versus underflow percent solids • Determination of underflow percent solids versus flocculant dosage • Comparing 190mm test rig underflow density results to that of the 2.4m

results at the same operating condition, to allow future scale up from the 190mm unit.



By gaining a better understanding of all these objectives we hope to improve site water management as well as tailings disposal.

Figure 2. SDGM Central Tailings Discharge In particular Outokumpu’s belief was that if a rotating bed could be prevented, permeability and usable dewatering area would be maintained. Hence, increasing underflow density, reducing flocculant consumption and reducing operating torque for the given density. Also, alleviating current thickener operating difficulties. The Paste Thickener R&D Programme was conducted in March, April and May 2003. The R&D programme consisted of three campaigns, which totalled a period of four weeks of testing.



Figure 3. General Arrangement of 2.4m Pilot Thickener



2.0 Summary The 2.4m pilot thickener achieved the objectives of the R&D programme in forming and then preventing the formation of a rotating bed and consequently obtaining increased underflow densities at reduced flocculant dosage rates. Tests 1 to 3 were operated as a bare rake with no pickets and in all three tests rotating beds were established. The torque increased and problems associated with pumping the underflow occurred. Test 4 utilised a horizontal beam, which prevented a rotating bed from forming. This test was not operated for a sufficient period to give any usable steady state results. Tests 5 to 25 were operated with a combination of stationary and rotating pickets which all prevented rotating bed formation. It was concluded that a combination of eight stationary and four rotating pickets at a rake arm tip speed of 11.3 m/min provided the most effective rake mechanism. That is, preventing rotating bed formation, providing adequate dewatering, compaction and permeability of the bed. This lead to improved underflow density and lower flocculant consumption. What we consider as our best operating result, achieved over a continuous 8 hour period and at the end of our R&D programme can be seen in Table 1 below: Test Rake Tip Speed U/F % Solids Loading Flocc. Dosage No. Mechanism m/min Solids t/m2h g/t 25 Stat. & Rot. pickets 11.3 65.3 0.91 18.5

Table 1. Best Operating Result

Comparative data was collected from the 2.4m pilot thickener and the 24m HCT on a daily basis to provide a concise summary of operating conditions. The 2.4m pilot thickener was operated at different conditions but the common element for tests 5 to 25 is that bed rotation was prevented. It was found that the 2.4m pilot thickener provided higher underflow densities for all except one of these tests when compared to the 24m HCT and this can be seen in Figure 4 overleaf. The one that did not provide a higher result was test 6. This was a test, which investigated high rake tip speed with full complement of rotating pickets. This test was successful in showing that this was not an operating set up to pursue.



Pilot vs Plant Thickener, SDGM

55.0

57.5

60.0

62.5

65.0

67.5

4 9 14 19 24

Test Number

Und

erflo

w %

Sol

ids

(w/w

)

Pilot Thickener Plant Thickener

Figure 4. Comparison of 2.4m Pilot Thickener & 24m HCT Underflow Densities

Yield stress is an important parameter and was tested extensively throughout the R&D programme. The testwork demonstrated that higher underflow densities lead to higher yield stresses. The results indicate that higher underflow densities can be achieved, however, consideration needs to be given to thickener drive torque rating and pumping of the underflow due to higher yield stresses.

Unsheared Yield Stress vs Underflow % Solids

y = 5E-10x6.2034

40

50

60

70

80

90

100

60.0 61.0 62.0 63.0 64.0 65.0 66.0Underflow % Solids (w/w)

Unsh

eare

d Yi

eld

Stre

ss

(Pa)

Figure 5. Unsheared Yield Stress vs Underflow % Solids



The 2.4m pilot thickener was fitted with two underflow pumps. A helical rotor pump and a centrifugal pump were both used to gauge the effects of shearing the material by pumping to tailings. It was found that a centrifugal pump would approximately halve the yield stress of the underflow.

79 5068 31

Before Centrifugul Pump

After Centrifugul Pump (Pa)

Table 2. Effect of Centrifugal Pump on Yield Stress The Haake Viscotester VT550 was used to simulate two stages of pumping with a centrifugal pump or one stage of pumping plus pipeline transport and these results were recorded as “1 x shear” and “2 x shear”. More details can be found in Section 3.6 Rheology Measurements.

Simulated 2 x shear

(Pa)202568 33

79 29


Simulated 1 x shear (Pa)

Table 3. Effect of Rheometer Shearing Events on Yield Stress

The R&D programme also tested the effects of using a centrifugal pump to recirculate underflow in the underflow cone of the thickener. It was possible to approximately halve the yield stress in the cone by recirculating the material with a centrifugal pump.

Unsheared Yield Stress (Pa)

Recirculated Yield Stress (Pa)

69 3791 62

58 2388 41

Table 4. Effect of Underflow Recirculation on Yield Stress



As the underflow density and hence unsheared yield stress of the material increased the operating torque also increased as illustrated in Figure 6 and 7 below.

Operating Torque vs Unsheared Yield Stress

y = 654.83e0.0107x

800

1000

1200

1400

1600

1800

2000

40 50 60 70 80 90 100

Unsheared Yield Stress

Ope

ratin

g To

rque

(Nm

)

Figure 6. Operating Torque vs Unsheared Yield Stress

Operating Torque vs Underflow % Solids

y = 24.327x2 - 3011.1x + 94468800

1000

1200

1400

1600

1800

2000

60 61 62 63 64 65 66 67

Underflow % Solids (w/w)

Ope

ratin

g To

rque

(Nm

)

Figure 7. Operating Torque vs Underflow % Solids Torque was measured by measuring hydraulic pressure to the drive hydraulic motor.



An ‘industry’ standard formula that is used to determine thickener drive capacity is; Maximum Operating Torque (Nm) = 14.63 x k x d2 (d = thickener diameter (m)) k varying depending essentially on material characteristics at the desired densities and the level at which the drive is to operate at for normal conditions. Normal operating torque can be say 33% of maximum operating torque or a more conservative approach would be 25%. To date the selection of k has generally come down to a review of the process and then determination based on years of experience. As the underflow densities being sought are increasing the determination of k needs additional information and this comes from rheology work – yield stress. The formula gives torque as the maximum operating torque (trip torque or cut out torque), not normal operating torque. Figures 8 below and 9 overleaf show k factor based on normal operating torque being 25% of maximum operating torque.

k Factor vs Unsheared Yield Stress

y = 0.6842x + 18.48130

40

50

60

70

80

90

100

40 50 60 70 80 90 100


k Fa

ctor

Figure 8. k Factor vs Unsheared Yield Stress



k Factor vs Underflow % Solids

y = 1.3045x2 - 161.68x + 5070.930

40

50

60

70

80

90

100

60 61 62 63 64 65 66 67


k Fa

ctor

Figure 9. k Factor vs Underflow % Solids Tests 15 to 17, 20, 21, 24 and 25 were at solids loadings of 0.71 to 0.89 t/m2h (typical of SDGM operating conditions) and are graphed below to illustrate the effects of varying the flocculant dosage. From this it seems that dosages higher than 20 to 25 g/t have no positive effect on underflow density.

Underflow % Solids versus Flocculant Dosage

60.561.061.562.062.563.063.564.064.565.065.5

10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0

Flocculant Dosage (g/t)

Unde

rflow

% S

olid

s (w

/w)

Figure 10. Underflow % Solids vs Flocculant Dosage



Testing was also conducted using Outokumpu’s 190mm laboratory/pilot rig to provide comparative data with the 2.4m pilot thickener. Three test runs showed strong correlation between the results of the 190mm rig vs 2.4m pilot thickener. The best results are shown below in Figure 11.

190mm versus 2.4m - U/F SG - May 4th

1.60

1.621.64

1.66

1.68

1.701.72

1.74

1.761.78

1.80

8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00Time of Day

U/F

SG (t

/m3)

190mm 2.4m

Figure 11. Comparison 190mm Laboratory Pilot Rig & 2.4m Pilot Thickener


Figure 12. 190mm Laboratory Pilot Rig


Figure 13. 2.4m Pilot Thickener



Date Test Mechanism Tip Feed Solids Flocculant Underflow Sheared Recirc. Unsheared 1 x shear Torque kSpeed Rate Loading Dosage Density Yield Stress Yield Stress Yield Stress Yield Stress Factorm/min t/h t/m2h g/t % Solids Pa Pa Pa Pa Nm

7 March 1 Bare Rake 7.5 2.89 0.64 29.8 66.7 - - - - - -8 March 2 Bare Rake 11.3 2.85 0.63 33.4 67.2 - - - - - -10 March 3 Bare Rake 11.3 2.57 0.57 36.7 67.1 - - - - - -11 March 4 Beam 11.3 3.27 0.72 28.6 67.3 - - - - - -12 March 5 Stat. & Rot. Pickets 11.3 3.51 0.78 38.3 63.4 - - - - - -13 March 6 Stat. & Rot. Pickets 22.6 2.48 0.55 39.0 (56) - - - - - -14 March 7 Stat. & Rot. Pickets 11.3 2.68 0.59 35.4 65.5 - 56 - 36 2373 2815 March 8 Stat. & Rot. Pickets 11.3 3.85 0.85 25.4 64.6 - 50 - 34 2503 3019 March 9 Stationary Pickets 11.3 2.59 0.57 36.9 64.8 - 73 - 42 2427 2920 March 10 Stationary Pickets 4.5 2.63 0.58 35.5 63.2 - 87 - 40 2817 3322 March 11 Stat. & Rot. Pickets 4.5 2.36 0.52 39.7 63.3 - 79 - 40 2678 3223 March 12 Stat. & 4 Rot. Pickets 4.5 2.72 0.60 34.3 63.0 - - - - 2808 3324 March 13 Stat. & 4 Rot. Pickets 4.5 2.53 0.56 36.8 63.8 - 101 - 55 2903 3425 March 14 Stationary Pickets 37.7 2.74 0.60 33.8 62.1 - - - - 2064 2411 April 15 Stat. & 4 Rot. Pickets 11.3 3.53 0.78 28.9 62.8 - - 63* 29 1408 1712 April 16 Stat. & 4 Rot. Pickets 11.3 3.51 0.77 23.4 63.2 - - 63* 33 1365 1612 April 16 Stat. & 4 Rot. Pickets 11.3 3.45 0.76 32.3 63.2 - - 71* 38 1430 1712 April 16 Stat. & 4 Rot. Pickets 11.3 3.20 0.71 50.6 62.2 - - - - - -13 April 17 Stat. & 4 Rot. Pickets 11.3 3.95 0.87 23.4 61.0 - 23 58* 28 1300 1513 April 17 Stat. & 4 Rot. Pickets 11.3 3.44 0.76 45.9 62.9 - 41 88* 35 1473 1713 April 17 Stat. & 4 Rot. Pickets 11.3 3.53 0.78 68.2 62.0 - 37 69* 22 1495 1814 April 18 Stat. & 4 Rot. Pickets 11.3 2.84 0.63 34.6 65.0 - 62 91* 41 1820 2215 April 19 Stat. & 4 Rot. Pickets 11.3 5.34 1.18 31.0 65.2 50 - 79* 29 1781 212 May 20 Stat. & 4 Rot. Pickets 11.3 3.63 0.80 30.8 61.8 31 - 68 33 1452 173 May 21 Stat. & 4 Rot. Pickets 11.3 3.77 0.83 17.3 61.5 - - 49 29 975 124 May 22 Stat. & 4 Rot. Pickets 11.3 2.71 0.60 25.6 62.8 - - 64 35 1206 145 May 23 Stat. & 4 Rot. Pickets 11.3 3.08 0.68 28.7 64.6 - - 83 39 1430 176 May 24 Stat. & 4 Rot. Pickets 11.3 4.01 0.89 19.0 63.8 - - 68 34 1105 137 May 25 Stat. & 4 Rot. Pickets 11.3 3.98 0.88 19.1 65.2 - - 58 31 1235 15

Tests 1 to 25 f igures are median values based on the daily logsheets.Tests 1 to 3 w ere initial tests and proved that rotating bed existed and the tests could be reproduced. * denotes YS includes measurements from floor sampling piontsTest 4 utilised the horizontal beam w hich proved that a rotating bed could be broken.

TABLE 5. 2.4 m THICKENER TESTWORK AT SUNRISE DAM GOLD MINE : MARCH - MAY 2003



3.0 Testwork and Procedures Twenty-five tests were conducted in the 2.4m pilot thickener. The thickener was operated based on “Procedure for 2.4m Pilot Thickener Operations" (Appendix 3).

Thickener Feed

Thickener Overflow

Overflow

Flocculant Addition

Underflow

2.4m diameter tThickener

Dilution Water

Figure 14. 2.4m Pilot Thickener Arrangement

3.1 Sample Preparation Feed slurry to the pilot rig was diluted to approximately 15% solids in the feedpipe using an external dilution pump based on the feed percent solids and dilution flow. Flocculant addition through a sparger was via the feedwell. The pilot thickener rig was run to simulate operating conditions in the 24m High Compression Thickener. The feed pump and pilot rig can be seen in Figures 15 and 16 overleaf.



Figure 15. Feed Pump and Header Tank Figure 16. Pilot Thickener Rig 3.2 Thickener Mechanisms The 2.4m pilot thickener was designed with four rake arms to provide a direct relationship to the 24m HCT. Initial tests were with bare rakes to simulate rotating bed formation as apparent with the 24m HCT. The next phase of the R&D programme utilised stationary and rotating pickets as can be seen in Figure 17 below.

Figure 17. Rakes with 8 Stationary and 4 Rotating Pickets



3.3 Flocculant Addition A flocculant survey was completed on 21 February 2003 to ensure that the correct concentration of 3.6 g/l was being administered. A timed sample was taken of the flocculant feed as a batch of flocculant was being prepared. Observations were made as to the procedure and the preparation of the flocculant. It was noted that the area was in a tidy condition and that the cone feeder was free from excess flocculant. A timed sample was taken and it was calculated that the flocculant was being made up at 3.3 g/l. Nalco 83370 is the flocculant used on site. Flocculant was pumped from the flocculant feed pump to the pilot flocculant feed tank before each test. Concentrated flocculant was diluted 10:1 in the flocculant addition manifold. Flocculant was pumped through a manifold and into the feedwell via a sparger. The flocculant dilution lines and manifold can be seen in Figures 18 and 19 respectively.

Figure 18. Flocculant Dilution Setup Figure 19. Flocculant Manifold

3.4 Measurements Measurements were taken on an hourly basis and recorded on a daily logsheet.

• Feed flow rate was measured via a Magflow meter and by recording the time taken to fill a 70 litre calibrated bucket.

• Feed dilution was obtained from a Magflow meter. • The flocculant rate was measured by timing the volume displacement on a

measuring cylinder. • The clarity of the overflow was determined by utilising a clarity wedge as can

be seen in Figure 20 overleaf. • Bed depth was determined by measuring the bed depth as was apparent

through the site glass.



• Underflow flow rate was determined by timing the discharge into a calibrated 10 litre bucket as can be seen in Figure 21. The remaining measurements were extracted from the PLC unit.

Figure 20. Observing Overflow Clarity Figure 21. Measuring U/F Flow Rate

3.5 Rotating Bed Determination A method for rotating bed determination was established based on previous experience. We decided that rotating bed determination would entail probing the bed for movement with a length of conduit and looking through the site window.

Figure 22. Rotating Bed Detection



3.6 Rheology Measurements Rheology measurements were taken utilising a Haake Viscotester VT550. The Viscotester was used to examine the rheological material parameters of the thickened slurry. Samples were taken from the pilot rig and poured into a beaker being careful not to shear the material. The OK 600 rotor was inserted into the beaker containing slurry. The rotor is rotated at a preset speed. The slurry exerts a resistance to the rotational movement and a torque reaction is applied on the measuring shaft. The slurry samples collected exhibited a changing viscosity, therefore showing non-Newtonian behaviour. The viscosity of a material can be defined as the relationship between shear stress and shear rate. It was found that by shearing the material the viscosity would decrease thus being shear thinning in nature. In relation to the rheological measurements slump testing was explored to give a direct relationship to yield stress. The procedure is to fill a small cylindrical cone of known volume and lift the cone to provide a slump that is measured by cylindrical rings. This gives a general idea on the pump ability and the yield stress of the slurry.

Figure 23. Slump Ring Test

Figure 24. Showing a Slump of Two Rings



The Viscotester was fitted with an Outokumpu custom made vane (OK 600), which is designed to measure yield stress values up to 600 Pa.

The yield stress was determined by recording the peak of a shear stress versus time curve. The yield stress was calculated at a shear rate of 0.1 s-1 over 60 s. This gave us an initial yield stress of the material. The sample was then exposed to a high shear rate of 10 s-1 over a 60 s period. This was initiated to gauge the effect of pumping the sample with a centrifugal pump. This stage was repeated to see the effects of two-stage pumping with centrifugal pumps, and to get a feel for the yield stress should the slurry structure be fully broken down.

Figure 25. Rheology Sample Figure 26. Laboratory and Rheometer

Illustration of Haake Yield Stress Printout

0

20

40

60

80

100

0 24 42 61 87 114 144 167 190 216 234 252 269 321 371

Time (secs)

Yiel

d St

ress

(Pa)

Yield Stress (Pa)

1 x shear event

2 x shear event

Figure 27. Illustration of Haake Yield Stress Printout



4.0 Results The scope of work for this study included the operation of the 2.4m pilot thickener and taking hourly samples. Detailed results from the R&D programme can be seen in the Daily Logsheets (Appendix 2). The summarised results can be seen in Table 10 on page 35. A feed slurry stream was taken directly from the 24m HCT feed pump discharge. A slurry sample was taken in a measuring cylinder and weighed before each test to determine the percent solids and establish the daily operating conditions. The feed percent solids varied from 45.3 % in test 7 to 56.0 % in test 25. A limitation of the testwork due to site water restrictions was the filling with raw process water at the start of each run. It was found that while operating the thickener the liquor SG would gradually increase from 1.020 g/cm3 to 1.090 g/cm3 due to the higher SG of the liquor in the process slurry. The underflow percent solids were corrected by utilising the liquor SG calibration curve, which can be seen in Figure 28 below.

Liquor SG Calibration

0.981

1.021.041.061.081.1

1 2 3 4 5 6 7 8 9 10

Time (h)

Liqu

or S

G (g

/cm

3)

Figure 28. Liquor SG Calibration Curve Figure 29. Hydrometer



The 2.4m pilot thickener was designed with four rake arms to provide a direct relationship to the 24m High Compression Thickener. Tests 1 to 3 were operated as a bare rake with no pickets at solids loading ranging from 0.56 to 0.67 t/m2h. It was noted that in all tests a rotating bed formed. None of these tests were run for adequate time to allow steady state results to be used for our analysis. Test 4 was at a solids loading of 0.72 t/m2h with a horizontal beam installed inside the tank. This was effective in preventing rotating bed formation whilst obtaining an underflow percent solids result of 67.1 % at a bed height of 1.0 m. This test was not run for an adequate time to allow steady state results to be used for our analysis. Tests 5 to 8 were run with a full complement of eight stationary and eight rotating pickets. Solids loading ranged from 0.55 t/m2h in test 6 to 0.85 t/m2h in test 8 with underflow percent solids varying between 56.0 % and 65.5 %. The low percent solids in test 6 can be attributed to underflow being recirculated from the cone to the sidewall, which disrupted the bed compaction. For tests 9 and 10 the rotating pickets were removed and the thickener ran with eight stationary pickets. Using rake tip speeds of 11.3 m/min and 4.5 m/min obtaining underflow percent solids of 64.8 % and 63.2 % respectively. The decrease in underflow percent solids can be attributed to the lower rake tip speed being unable to maintain the required solids transportation to the underflow. Test 11 to 14 explored various picket combinations as well as rake tip speeds ranging from 4.5 m/min to 37.7 m/min. It was found that at the higher rake tip speed only 62.1 % underflow solids was achievable, most likely due to eddies within the thickener that were not conducive to settling. It was concluded that a combination of eight stationary and four rotating pickets at a rake arm tip speed of 11.3 m/min provided the most effective rake mechanism. That is, preventing rotating bed formation, providing adequate dewatering, compaction and permeability of the bed. This lead to improved underflow density and lower flocculant consumption. All subsequent tests, 14 to 25, were run with the configuration of four rotating and eight stationary pickets at a rake tip speed of 11.3 m/min. To achieve a higher density generally requires a lower solids throughput for a given thickener area and an increase in bed depth. This can be related to the solids loading in tonnes per square metre per hour of thickener area. The solids loading in the pilot campaign varied from 0.52 t/m2h to 1.18 t/m2h however generally focussed on the solids loading applicable to SDGM’s 24m HCT. Comparative data was collected from the 2.4m pilot thickener and the 24m HCT on a daily basis to provide a concise summary of operating conditions.



The 2.4m pilot thickener was operated at different conditions but the common element for tests 5 to 25 is that bed rotation was prevented. It was found that the 2.4m pilot thickener provided higher underflow densities for all except one of these tests when compared to the 24m HCT and this can be seen in Figure 30. The one that did not provide a higher result was test 6. This was a test, which investigated high rake tip speed with full complement of rotating pickets. This test was successful in showing that this was not an operating set up to pursue.

Pilot vs Plant Thickener, SDGM

55.0

57.5

60.0

62.5

65.0

67.5

4 9 14 19 24

Test Number

Und

erflo

w %

Sol

ids

(w/w

)

Pilot Thickener Plant Thickener

Figure 30. Comparison of 2.4m Pilot Thickener & 24m HCT Underflow Densities

Yield stress is an important parameter and was tested extensively throughout the R&D programme. The testwork demonstrated that higher underflow densities lead to higher yield stresses. The results indicate that higher underflow densities can be achieved, however, consideration needs to be given to thickener drive torque rating and pumping of the underflow due to higher yield stresses.



Unsheared Yield Stress vs Underflow % Solids

y = 5E-10x6.2034

40

50

60

70

80

90

100

60.0 61.0 62.0 63.0 64.0 65.0 66.0Underflow % Solids (w/w)

Unsh

eare

d Yi

eld

Stre

ss

(Pa)

Figure 31. Unsheared Yield Stress vs. Underflow % Solids The 2.4m pilot thickener was fitted with two underflow pumps. A helical rotor pump and a centrifugal pump were both used to gauge the effects of shearing the material by pumping to tailings. It was found that a centrifugal pump would approximately halve the yield stress of the underflow.

79 5068 31


After Centrifugul Pump (Pa)

Table 6. Effect of Centrifugal Pump on Yield Stress The Haake Viscotester VT550 was used to simulate two stages of pumping with a centrifugal pump or one stage of pumping plus pipeline transport and these results were recorded as “1 x shear” and “2 x shear”. More details can be found in Section 3.6 Rheology Measurements.

Simulated 2 x shear

(Pa)202568 33

79 29


Simulated 1 x shear (Pa)

Table 7. Effect of Rheometer Shearing Events on Yield Stress The settling of particles is governed by hindered settling which is directly related to Stokes law. The slurry exhibited non-Newtonian fluid behaviour due to the flow curve of shear stress versus shear rate being non-linear.



Illustration of Haake Yield Stress Printout

0

20

40

60

80

100

0 24 42 61 87 114 144 167 190 216 234 252 269 321 371

Time (secs)

Yiel

d St

ress

(Pa)

Yield Stress (Pa)

1 x shear event

2 x shear event

Figure 32. Illustration of Haake Yield Stress Printout

The R&D programme also tested the effects of using a centrifugal pump to recirculate underflow in the underflow cone of the thickener. It was possible to approximately halve the yield stress in the cone by recirculating the material with a centrifugal pump.


Recirculated Yield Stress (Pa)

69 3791 62

58 2388 41

Table 8. Effect of Underflow Recirculation on Yield Stress



As the underflow density and hence unsheared yield stress of the material increased the operating torque also increased as illustrated in Figure 33 and 34 below.

Operating Torque vs Unsheared Yield Stress

y = 654.83e0.0107x

800

1000

1200

1400

1600

1800

2000

40 50 60 70 80 90 100

Unsheared Yield Stress

Ope

ratin

g To

rque

(Nm

)

Figure 33. Operating Torque vs Unsheared Yield Stress

Operating Torque vs Underflow % Solids

y = 24.327x2 - 3011.1x + 94468800

1000

1200

1400

1600

1800

2000

60 61 62 63 64 65 66 67


Ope

ratin

g To

rque

(Nm

)

Figure 34. Operating Torque vs Underflow % Solids Torque was measured by measuring hydraulic pressure to the drive hydraulic motor.



An ‘industry’ standard formula that is used to determine thickener drive capacity is; Maximum Operating Torque (Nm) = 14.63 x k x d2 (d = thickener diameter (m)) k varying depending essentially on material characteristics at the desired densities and the level at which the drive is to operate at for normal conditions. Normal operating torque can be say 33% of maximum operating torque or a more conservative approach would be 25%. To date the selection of k has generally come down to a review of the process and then determination based on years of experience. As the underflow densities being sought are increasing the determination of k needs additional information and this comes from rheology work – yield stress. The formula gives torque as the maximum operating torque (trip torque or cut out torque), not normal operating torque. Figures 35 below and 36 overleaf show k factor based on normal operating torque being 25% of maximum operating torque.

k Factor vs Unsheared Yield Stress

y = 0.6842x + 18.48130

40

50

60

70

80

90

100

40 50 60 70 80 90 100


k Fa

ctor

Figure 35. k Factor vs Unsheared Yield Stress



k Factor vs Underflow % Solids

y = 1.3045x2 - 161.68x + 5070.930

40

50

60

70

80

90

100

60 61 62 63 64 65 66 67


k Fa

ctor

Figure 36. k Factor vs Underflow % Solids Tests 15 to 17, 20, 21, 24 and 25 were at solids loadings of 0.71 to 0.89 t/m2h (typical of SDGM operating conditions) and are graphed below to illustrate the effects of varying the flocculant dosage. From this it seems that dosages higher than 20 to 25 g/t have no positive effect on underflow density.

Underflow % Solids versus Flocculant Dosage

60.561.061.562.062.563.063.564.064.565.065.5

10.0 20.0 30.0 40.0 50.0 60.0 70.0 80.0

Flocculant Dosage (g/t)

Unde

rflow

% S

olid

s (w/

w)

Figure 37. Underflow % Solids vs Flocculant Dosage



At the end of the R&D programme test 25 was run with a solids loading of 0.88 t/m2h to simulate SDGM plant throughput and at a lower flocculant dosage of 19.1 g/t. This resulted in underflow solids of 65.2 %. This test, we consider as our best operating result, achieved over a continuous 8-hour period and can be seen in Table 9 below: Test Rake Tip Speed U/F % Solids Loading Flocc. Dosage No. Mechanism m/min Solids t/m2h g/t 25 Stat. & Rot. pickets 11.3 65.2 0.88 19.1

Table 9. Best Operating Result

Testing was also conducted using Outokumpu’s 190mm laboratory/pilot rig to provide comparative data with the 2.4m pilot thickener. The 190mm rig also confirmed strong tendency for the SDGM material to form a rotating bed. The result of this can be seen by the damage to the first version of rotating and static pickets. The pickets were subsequently strengthened for the three comparison tests.

Figure 38. 190mm Twisted Rotating and Static Pickets



The three test runs showed strong correlation between the results of the 190mm rig vs 2.4m pilot thickener. The three results are shown in Figures 39, 40 below and Figure 41 overleaf

190mm versus 2.4m - U/F SG - May 3rd

1.60

1.62

1.64

1.66

1.68

1.70

1.72

1.74

1.76

1.78

1.80

7:00 8:00 9:00 10:00 11:00 12:00 13:00 14:00

Time of Day

U/F

SG (t

/m3)

190mm 2.4m

Figure 39. Comparison of 190mm Pilot Rig & 2.4m Pilot Thickener Run 1

190mm versus 2.4m - U/F SG - May 4th

1.60

1.621.64

1.66

1.68

1.701.72

1.74

1.761.78

1.80

8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00Time of Day

U/F

SG (t/

m3)

190mm 2.4m




2.4m versus 190mm - U/F SG - May 5th

1.60

1.65

1.70

1.75

1.80

1.85

8:00 9:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00Time of Day

U/F

SG

(t/m

3)

190mm 2.4m




Date Test Mechanism Tip Feed Solids Flocculant Underflow Sheared Recirc. Unsheared 1 x shear Torque kSpeed Rate Loading Dosage Density Yield Stress Yield Stress Yield Stress Yield Stress Factorm/min t/h t/m2h g/t % Solids Pa Pa Pa Pa Nm

7 March 1 Bare Rake 7.5 2.89 0.64 29.8 66.7 - - - - - -8 March 2 Bare Rake 11.3 2.85 0.63 33.4 67.2 - - - - - -10 March 3 Bare Rake 11.3 2.57 0.57 36.7 67.1 - - - - - -11 March 4 Beam 11.3 3.27 0.72 28.6 67.3 - - - - - -12 March 5 Stat. & Rot. Pickets 11.3 3.51 0.78 38.3 63.4 - - - - - -13 March 6 Stat. & Rot. Pickets 22.6 2.48 0.55 39.0 (56) - - - - - -14 March 7 Stat. & Rot. Pickets 11.3 2.68 0.59 35.4 65.5 - 56 - 36 2373 2815 March 8 Stat. & Rot. Pickets 11.3 3.85 0.85 25.4 64.6 - 50 - 34 2503 3019 March 9 Stationary Pickets 11.3 2.59 0.57 36.9 64.8 - 73 - 42 2427 2920 March 10 Stationary Pickets 4.5 2.63 0.58 35.5 63.2 - 87 - 40 2817 3322 March 11 Stat. & Rot. Pickets 4.5 2.36 0.52 39.7 63.3 - 79 - 40 2678 3223 March 12 Stat. & 4 Rot. Pickets 4.5 2.72 0.60 34.3 63.0 - - - - 2808 3324 March 13 Stat. & 4 Rot. Pickets 4.5 2.53 0.56 36.8 63.8 - 101 - 55 2903 3425 March 14 Stationary Pickets 37.7 2.74 0.60 33.8 62.1 - - - - 2064 2411 April 15 Stat. & 4 Rot. Pickets 11.3 3.53 0.78 28.9 62.8 - - 63* 29 1408 1712 April 16 Stat. & 4 Rot. Pickets 11.3 3.51 0.77 23.4 63.2 - - 63* 33 1365 1612 April 16 Stat. & 4 Rot. Pickets 11.3 3.45 0.76 32.3 63.2 - - 71* 38 1430 1712 April 16 Stat. & 4 Rot. Pickets 11.3 3.20 0.71 50.6 62.2 - - - - - -13 April 17 Stat. & 4 Rot. Pickets 11.3 3.95 0.87 23.4 61.0 - 23 58* 28 1300 1513 April 17 Stat. & 4 Rot. Pickets 11.3 3.44 0.76 45.9 62.9 - 41 88* 35 1473 1713 April 17 Stat. & 4 Rot. Pickets 11.3 3.53 0.78 68.2 62.0 - 37 69* 22 1495 1814 April 18 Stat. & 4 Rot. Pickets 11.3 2.84 0.63 34.6 65.0 - 62 91* 41 1820 2215 April 19 Stat. & 4 Rot. Pickets 11.3 5.34 1.18 31.0 65.2 50 - 79* 29 1781 212 May 20 Stat. & 4 Rot. Pickets 11.3 3.63 0.80 30.8 61.8 31 - 68 33 1452 173 May 21 Stat. & 4 Rot. Pickets 11.3 3.77 0.83 17.3 61.5 - - 49 29 975 124 May 22 Stat. & 4 Rot. Pickets 11.3 2.71 0.60 25.6 62.8 - - 64 35 1206 145 May 23 Stat. & 4 Rot. Pickets 11.3 3.08 0.68 28.7 64.6 - - 83 39 1430 176 May 24 Stat. & 4 Rot. Pickets 11.3 4.01 0.89 19.0 63.8 - - 68 34 1105 137 May 25 Stat. & 4 Rot. Pickets 11.3 3.98 0.88 19.1 65.2 - - 58 31 1235 15

Tests 1 to 25 f igures are median values based on the daily logsheets.Tests 1 to 3 w ere initial tests and proved that rotating bed existed and the tests could be reproduced. * denotes YS includes measurements from floor sampling piontsTest 4 utilised the horizontal beam w hich proved that a rotating bed could be broken.

TABLE 10. 2.4 m THICKENER TESTWORK AT SUNRISE DAM GOLD MINE : MARCH - MAY 2003



5.0 Conclusions and Recommendations In conclusion, the 2.4m pilot thickener achieved the objectives of the R&D programme in forming and then preventing the formation of a rotating bed and consequently obtaining increased underflow densities at reduced flocculant dosage rates. It was concluded that in the 2.4m pilot thickener that a combination of eight stationary and four rotating pickets at a tip speed of 11.3 m/min provided the most effective rake mechanism. That is, preventing rotating bed formation, providing adequate dewatering, compaction and permeability of the bed. This lead to improved underflow density and lower flocculant consumption. Yield stress is an important parameter and was tested extensively throughout the R&D programme. It was found that by shearing the material the yield stress would decrease due to its shear thinning nature. The 2.4m pilot thickener was fitted with two underflow pumps. A helical rotor pump and a centrifugal pump were both used to gauge the effects of shearing the material by pumping to tailings. It was found that a centrifugal pump would essentially halve the yield stress of the material. The results indicate that higher underflow densities can be achieved however consideration needs to be given to thickener drive torque rating and pumping of the underflow due to higher yield stresses. The R&D programme also concluded that flocculant dosages higher than 20 to 25 g/t have no positive effect on underflow density. Testing was also conducted using Outokumpu’s 190mm laboratory pilot rig to provide comparative data with the 2.4m pilot thickener. The testwork showed strong correlation between the two. Should SDGM desire higher densities than currently being achieved, we believe from this R&D programme that this is possible, however modifications to the existing 24m HCT would be required. These modifications would essentially include forced feed dilution, rotating bed prevention system, cancellation of rake lifting system, increase in the overall drive and mechanism torque capacity and installation of more reliable bed level detection device. We believe that a feed of 50% plus to the thickener feedwell is too high to achieve efficient dilution without mechanical mixing. Hence inclusion of forced feed dilution system – TurboDil.



We believe that a rotating bed prevention system could be designed and fitted to the 24m HCT and by doing so improve overall thickener performance. To operate effectively this system requires the bed depth to be approximately 500mm above the bottom of the static pickets. Until this level is reached we believe the bed will be rotating. As such, we feel that rake lift should be cancelled so that the maximum length of static pickets can be installed. Should the desired operating underflow density be 65% w/w from our k Factor vs Underflow % solids graph (Figures 9 & 36) k Factor would be 75 giving a drive and mechanism rating of 632,000 Nm. The current drive and mechanism rating is 350,000 Nm. Given that the rake lift is to be cancelled and that the gearbox selection between 632,000 and 800,000 Nm is of little cost difference we would recommend going to 800,000 Nm for the new drive. As bed level is now a more important operating parameter we believe a more reliable detection device should be installed.



Appendix 1

Photographs



Appendix 2

Logsheets



Appendix 3

Procedures



Appendix 4

Lab Simulation of Underflow % Solids vs Unsheared Yield Stress




Late June 2003 Outokumpu requested and received a sample of underflow from SDGM’s 24m HCT. This sample was used in Outokumpu’s laboratory to construct a lab generated yield stress curve at different percent solids. Note for this construction actual measured specific gravities were used for calculation for percent solids (w/w)

Percent Solids Vs Yield Stress (Solid SG 2.86, Liquor SG 1.12)

0

50

100

150

200

250

300

350

400

60 61 62 63 64 65 66 67 68 69

Percent Solids (w/w)

Yie

ld S

tres

s (P

a)

0 Shear 1st Shear 2nd Shear

Figure 42. Underflow Percent Solids vs Yield Stress

2.4m Thickener Preliminary Report Rev0

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