Bjrkdal Gold Mines mill discharge circuit poses various challenges, due to it consisting of an interactive collection of sumps that feed the gravity separation circuit. For optimal gravity circuit performance, the hydrocyclones and spirals require a constant feed flowrate. An MPC strategy was implemented to balance the volume between four mill discharge tanks in order to attain a constant gravity feed flowrate. The increased stability in the mill discharge circuit has resulted in an increase of 1% recovery from the gravity separation circuit. Further processing of the gold ore at Bjrkdal includes a Knelson separator which feeds a flotation circuit. Due to the flushing cycle of the Knelson separator, the flotation circuit experiences extreme volume fluctuations at intermittent times. Implementation of a model-based feedforward with stabilising PID controller compensated for these Knelson flush volume fluctuations, which has resulted in a more constant pulp level. This has translated to a more stable flotation circuit and 2.1% increase in recovery around this section. Once the flotation circuit had been stabilised, it was considered for optimisation. A flowrate measurement was installed on the combined Rougher-Scavenger concentrate stream. This information is being used to target a desired mass pull from the two flotation banks by manipulating the level and air setpoint values of the individual cells. Thus far, implementation of this flotation optimisation strategy shows promising results, however not enough data has been collected to make any substantial conclusions.
CITATION:Saffy, M, Mashakane, T and Hopstadius, P, 2019. Control and optimisation of a gold milling and flotation circuit, in Proceedings World Gold 2019, pp 640646 (The Australasian Institute of Mining and Metallurgy: Melbourne).