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Table 3: HPGR Test Results for Sample A

Feed Open Circuit TestsClosedCircuitTest

Pressure Setting bar 30 40 50 40Characterization DataBond Ball Mill Wi(CIMM)

13.3 11.2 11.4 10.8

Bond Ball Mill Wi(Polysius)

13.6 12.9

Lab Mill Index (kWh.mt)At 100% -90m

12.1 8.8

Specific Wear Rate g/t 29.5

Test ResultsHPGR Throughput Ratetph

12.2 10.8 11.6 10.9

Fresh Feed P80 mm 20.8HPGR Feed P80 mm 20.8 20.8 20.8 17.5HPGR Discharge P80mm

7.6 6.4 5.2 6.5

Screen Undersize P80mm

1.8

HPGR PowerConsumption kW 13.0 16.6 12.4 16.0

Product Flake Thicknessmm

23.2 22.1 22.5 21.2

HPGR Grinding ForcekN

397 551 690 563

Specific Press ForceN/mm

2

2.66 3.70 4.63 3.78

HPGR Specific EnergykWh/t

1.07 1.53 1.85 1.47

HPGR SpecificThroughput ts/m

3h

281 251 267 251

HPGR Specific PowerkWs/m

244.7 57.2 73.7 55.1

Screen Undersize % 55.9Circulating Load (o/s :u/s)

0.79

Circuit Specific EnergykWh/t

2.63

There is a general and consistent reduction in ball mill work indices withincreasing pressure in the open circuit samples. In the closed circuit locked cycle test the level of reduction in Bond ball mill work index is

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17% for sample A and 12% for samples B and C. It is assumed thatthis reduction is as a result of micro-cracking or other compressive forceeffects on the samples produced by the action of the HPGR. Earlier

Table 4: HPGR Test Result s for Sample B

Feed Open Circuit TestsClosedCircuitTests

Pressure Setting bar 30 40 50 40Characterization Data

Bond Ball Mill Wi(CIMM)

14.7 13.7 13.6 12.6 13.1

Bond Ball Mill Wi(Polysius)

15.1 14.4

Lab Mill Index (kWh/mt)At 100% -90m

12.9 10.4

Specific Wear Rate g/t 23.7Test Results

HPGR Throughput Ratetph

13.3 11.8 11.9 11.0

Fresh Feed P80 mm 20.0HPGR Feed P80 mm 20.0 20.0 20.0 15.0HPGR Discharge P80mm 7.0 7.0 5.7 6.8

Screen Undersize P80mm

2.1

HPGR PowerConsumption kW

13.6 18.7 21.6 16.3

Product FlakeThickness mm

24.9 23.5 22.3 23.7

HPGR Grinding ForcekN

412 589 707 561

Specific Press ForceN/mm

2

2.76 3.95 4.74 3.76

HPGR Specific EnergykWh/t

1.02 1.59 1.82 1.49

HPGR SpecificThroughput ts/m

3h

307 272 275 253

HPGR Specific PowerkWs/m

246.9 64.4 74.5 56.3

Screen Undersize % 54.6

Circulating Load (o/s :u/s)

0.83

Circuit Specific EnergykWh/t

2.73

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tests undertaken at Anglo Research (Smit, 2005) showed encouragingflotation response of the reconstituted laboratory HPGR /ball millsamples from a single Los Bronces ore sample (Figure 2 next page).

Table 5: HPGR Test Results for Sample C

Feed Open Circuit TestsClosedCircuitTest

Pressure Setting bar 30 40 50 40Characterization Data

Bond Ball Mill Wi(CIMM)

14.7 13.6 12.7 12.5 12.8

Bond Ball Mill Wi(Polysius)

14.4 13.3

Lab Mill Index (kWh/mt)At 100% -90m

12.1 9.9

Specific Wear Rate g/t 16.0Test Results

HPGR Throughput Ratetph

11.5 11.7 11.2 10.9

Fresh Feed P80 mm 13.0HPGR Feed P80 mm 13.0 13.0 13.0 13.0HPGR Discharge P80mm 6.0 5.2 5.7 8.2

Screen Undersize P80mm

2.3

HPGR PowerConsumption kW

11.1 18.7 18.3 16.3

Product Flake Thicknessmm

21.9 23.5 21.4 23.7

HPGR Grinding ForcekN

389 589 660 561

Specific Press ForceN/mm

2

2.61 3.95 4.43 3.76

HPGR Specific EnergykWh/t

0.97 1.59 1.64 1.49

HPGR SpecificThroughput ts/m

3h

266 272 258 253

HPGR Specific PowerkWs/m

238.3 64.4 63.2 56.2

Screen Undersize % 57.8

Circulating Load (o/s :u/s)

0.73

Circuit Specific EnergykWh/t

2.58

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Based on Figure 2, rougher flotation tests were undertaken on thecentre products from the semi-industrial closed circuit tests. Theobjective was to assess if there was a change in flotation performance ifprepared in a conventional laboratory crusher-ball mill as opposed to

HPGR-ball mill preparation. Flotation kinetics were assessed using theKlimpel flotation rate equation. Results are summarized in table 6.

Figure 2: Rougher flotation response

Table 6: Summary of flo tation results

Feed Open Circuit TestsClosedCircuitTest

Pressure Settingbar

30 40 50 40

Sample AHead, %Cu 0.42 0.53 0.58 0.52Concentrate, %Cu 8.02 8.04 8.9 8.12Cu Recovery, % 91.4 91.2 90.6 90.4R, % 95.9 95.9 98.7 95.7k, min-1 3.5 3.3 1.7 3

Sample BHead, %Cu 0.74 0.75 0.76 0.78 0.72Concentrate, %Cu 10.05 8.81 8.94 8.45 8.51Cu Recovery, % 79.5 78.7 81.5 77.4 81.9R, % 84.1 83.3 86.4 83.0 87.1k, min-1 2.8 2.6 2.5 2.2 2.4

Sample CHead, %Cu 1.22 1.26 1.25 1.23 1.20Concentrate, %Cu 11.6 12.1 11.5 10.7 11.7Cu Recovery, % 90.4 91.4 91.4 90.4 91.7R, % 98.6 95.3 96.7 97.6 97.9k, min-

1 1.9 3.7 2.7 1.9 2.5

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The results indicate that there is insufficient information to quantify aneventual potential benefit in flotation, but it is concluded that there is nonegative effect of using the HPGR on the rougher grade-recoveryrelationship as a result of using this technology.

CONCEPTUAL DESIGN FOR THE LOS BRONCES HPGR CIRCUIT

The preferred circuit under consideration for the use of HPGRs is inFigure 3.

Figure 3: Conceptual HPGR Circu it

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The conceptual design criteria to process 80 000 tpd additionalthroughput are:

Secondary crushing circuit

Overall availability = 85%Circuit feed size = 80%-150mmSG of ore = 2.8Product size = 98%-50mm

High Pressure Grinding Rolls circuitOverall availability = 93%Design screen aperture = 8mm

Ball Mill circui t

Overall availability = 96%Design Bond Ball Mill Work Index = 15.2 kWh/stDesign product size = 80%-180m

Simulations were carried out by Polysius on the HPGR circuit using aproprietary simulator (Klymowsky and Lui, 1997) using the test workresults and scaling them to the design requirements. The main factorsthat were different from the test work and the design criteria werethroughput rates, feed particle size distributions to the circuit and ore

hardness.

Initial ball mill sizing were also determined through simulations usingJKSimMet V5.1, and are based on surveys carried out at Los Bronces.The ball mill dimensions were independently checked using reducedrecovery simulations (Barratt, 1989) for segregation of finished material(simulated cyclone overflow) and feeding simulated cyclone underflow(scalped product) to the ball mills. Whereas the proportion of fines (orfinished product in the screen undersize) might be viewed as being

higher than expected, it is interesting to note that the projectedoperating work indices for secondary ball milling when using thereduced recovery simulations are in the same range as those whichhave been estimated by the JK SimMet model.

The resultant equipment details are:

Secondary crushing circuitNumber of screens = 3Screen aperture size = 50 mm

Screen area (per screen) = 30.1 m2Number of crushers = 3Crusher type = Standard coneClosed Size Setting = 30 mm

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Installed Power (total) = 2 238 kWSpecific energy consumption = 0.4 kWh/t

High Pressure Grinding Rolls circuit

Screen undersize size distribution = 80%-2.115mmCirculating load (% of fresh feed) = 152%Intermediate stockpile capacity = 30000 tNumber of HPGR machines = 2Roll diameter = 2.4mRoll length = 1.75mPower Required (per HPGR) = 4760 kWInstalled Power (per HPGR) = 5600 kWSpecific energy consumption = 2.66 kWh/t

Ball Mill circuitNumber of ball mills = 2Ball mill diameter = 7.53mBall mill length = 11.25mPower required (per mill) = 13648 kWInstalled Power (per mill) = 13800 kWSpecific energy consumption = 7.87 kWh/t

Figure 4 is an example layout developed for the HPGR-ball mill circuit.

Figure 4: Layout of HPGR Circuit

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OPERATING COSTS

The operating cost for the HPGR-ball mill circuit was estimated basedon the conceptual design, information gathered from the test work

performed and actual operational data from Los Bronces. The annualoperating costs are estimated to be 1.48 US$/t.

The operating costs were also compiled, on the same basis, for a SABCcircuit similar to the existing circuit at Los Bronces (Figure 5). Theoperating costs are estimated to be 1.85 US$/t.

To thickening

and flotation

From Mine

PrimaryCrusher

CoarseOre

Stockpile

PebbleCrusher

Ball Mill

Hydrocyclones

SAGMill

Screen

Figure 5: SABC Circuit

The energy consumption per tonne of the HPGR-ball mill circuit iscalculated as 13.02 kWh/t (includes all ancillaries) compared with acalculated value of 16.21 kWh/t for the SABC circuit

There is an estimated operating cost difference of 0.37 US$/t in favourof the HPGR circuit, consisting of

Energy savings - estimated to be lower by 0.22 US$/t, reflecting thelower energy consumption per tonne of the HPGR-ball mill circuit at13.02 kWh/t (including all ancillaries) compared with 16.21 kWh/t forthe SABC circuit.

Materials costs - estimated to be lower by 0.15 US$/t reflecting a5000 hour average life for roller tyres and savings in grinding mediaand liners.

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