Benchmarking: Bond - Cadia East
Contents
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.
- Wi_{C} = 30 (metric)
- Wi_{RM} = 26.5 (metric)
- Wi_{BM} = 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
Modelling
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:
- F_{80} = 80 mm
- P_{80} = 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
E_{SAG} | E_{ball} | E_{total} | 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.
Discussion
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 E_{total} = 26.8 kWh/t; still 13% high.
- The E_{ssbm} 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 E_{ssbm} = 24.3 kWh/t which is still less than the survey E_{total}. Very odd result that a SABC circuit is more efficient than an SSBM (ergo, HPGR) circuit on such a hard ore.