The discharge mechanism of a mill is an important design characteristic, as it can have a significant impact on the throughput of the mill. The flow characteristics through the mill are commonly discussed in terms of the slurry head that builds up within the mill, grinding chamber. This property is referred to as slurry hold-up.
Pulp lifters are a commonly found discharge mechanism in semi-autogenous grinding. However, conventional designs are not efficient (relative to grate only discharge) in transporting slurry from the mill. This is primarily due to a lack of lifter capacity.
Alternately, an open-ended, or grate only, discharge mechanism can be used to achieve more efficient slurry discharge. However, this change would have a significant impact on the design and operation of the mill. Each of these differences has an impact on the economics associated with the mill.
The purpose of this thesis is to provide a comparison of semi-autogenous grinding (SAG) mills operating with different discharge mechanisms, by assessing the following hypothesis:
A SAG mill operating with an open-ended discharge mechanism will give better overall economics than one operating with a pulp lifter arrangement, where the mills operate to give equivalent grinds.
All factors, including mill design, plant layout, and operating conditions, which impact the cost of the mill and the surrounding comminution circuit will be assessed.
The Mt Keith operation in Western Australia is to be used as a case study, providing data for a SAG in operation with pulp lifters. The mill design will then be converted to an open-ended discharge, using current models available.