Benchmarking: Bond - Cadia East

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Benchmarking: Bond/Barratt - Cadia

Engelhardt, D., Robertson, J., Lane, G., Powwel, M.S. and Griffin, P., Cadia Expansion - From open pit to block cave and beyond. Proceedings of MetSoc 2012.

Design criteria and plant trial of underground Cadia East ore

Ore characterization

  • blased underground ore, secondary crushed to 80 mm.
    • WiC = 30 (metric)
    • WiRM = 26.5 (metric)
    • WiBM = 21.4 (metric)
    • DWI = 9.9
    • density = 2.7 t/m³

The ore was reported blasted undergrond (block caving had not yet started). Particle size distribution given as two points which confirm a Bond-compatible "root-2" PSD.

  • 80% passing 80 mm
  • 20% passing 5 mm


Details of the mill operating conditions are not given, but the power draw at the shell is given.

  • 15.737 MW SAG mill power draw
  • 19.509 MW ball mill power draw

Circuit operating conditions:

  • F80 = 80 mm
  • P80 = 140 µm
  • instantaneous throughput = 1482 t/h

The mill load, ball charge and pulp density was tweaked to mimic these power draws, corresponding to:

  • SAG operating 9% v/v balls, 25.5% v/v total filling and 78% of critical speed (Austin model has fixed %solids)
  • ball mills operating 37% v/v total filling and 70% w/w solids (fixed speed mills, 72% of critical speed)

The ball load required to match the reported power draw is very high, and could only be achieved with a significant reduction in the trunnion diameter (using ball retaining rings). Moreover, the motors are predicted to be operating at 100.5% of their rated output power to achieve the indicated power draw.

Model results

ESAG Eball Etotal Throughput
Model 12.31 kWh/t 14.94 kWh/t 27.7 kWh/t 1243 t/h
Measured 10.6 kWh/t 13.2 kWh/t 23.8 kWh/t 1482 t/h
Difference 1.71 kWh/t 1.74 kWh/t 3.9 kWh/t -239 t/h
Difference 16.13% 13.18% 16.39% -16.13%

The predicted transfer size needed to balance the power draw between primary & second mills is very coarse, 5 mm.


There is a substantial difference between the survey and the predictions. Some observations:

  • The rod mill work index was determined on an apparatus with smooth liners. This can cause a difference of 2-3 kWh/t versus the wave-liner apparatus specified by Bond. Using a rod mill work index of 24.0 kWh/t gives Etotal = 26.8 kWh/t; still 13% high.
  • The Essbm predicts the energy required for a "standard" secondary crushing & ball milling plant that is believed to be one of the most energy efficient types of grinding circuits. This ore has Essbm = 24.3 kWh/t which is still less than the survey Etotal. Very odd result that a SABC circuit is more efficient than an SSBM (ergo, HPGR) circuit on such a hard ore.