A copper concentrator has been designed provisionally with a 3 stage crushing circuit. The final stage is in closed circuit with a screening system. For production of feed suitable for flotation, a rod mill/ ball mill combination has been selected.

1. Draw the complete comminution circuit for this mineral processing plant. Use correct symbols for the equipment.                                                                     
2. 
   
3. Using the information listed below, estimate the size of mills required. State any assumptions made. Also sketch the complete comminution circuit for this mineral processing plant.   

 

Data Available

• Overall plant throughput                                   = 12,000t/day
• Estimated grinding circuit availability              = 93%

Sizing Data

• Feed from crushing plant                                 = 80% passing 17 mm
• Suggested rod mill discharge size                   = 80% passing 1.2 mm
• Flotation feed sizing                                        = 80% passing 75µm

Bond Grindability Data:

• Rod mill work index                                        = 13.5 kWh/t
• Bond mill work index                                      = 12.5 kWh/t

 

Mills Operating Data:

• Both mills operate at 75% of their critical speeds
• Aspect ratio (L/D) of the ball mill is 1
• Aspect ratio (L/D) of the rod mill is 2
• Mill fill factor (J) for both mills is 0.4
• K(J) for the ball mill is K(J) = J(J-1)²
• K(J) for the ball mill is K(J) = J(1-J)
• Assume the Bond Power model for ball mill also applies to the rod mill
• Assume a toe angle of 30˚ for both mills