A flotation circuit is a highly complex chemical process used to separate and concentrate a particular substance from the solid or liquid in which it resides. This includes metals from raw mined materials, but also removal of solids and other pollutants within wastewater. In mining processes, flotation optimisation can involve changing concentrate flow rates, or manipulating the residence time of minerals.
Where flotation circuits have more complex instrumentation, optimisation can involve mass pull, reagent concentrations, and level and airflow set-points.
Optimisation of mass pull refers to identifying the optimum percentage of material (mass) sent to flotation and pulled into the concentrate. The aim is to maximise the percentage of metal in the concentrate at each step.
Reagents, such as frothers, modifiers and activators, typically have a long response time. Effective optimisation can be achieved through adjusting the reagent concentration. Reagents can also be implemented at the start of the process or at intermediate points, depending upon their concentration and the length of time before they start having an effect on the flotation performance.
Similarly, airflow within the flotation process can be altered and can provide rapid response to flow variations.
Set-points for the level in a flotation cell and for the aeration airflow can be optimised to improve the concentrate grade and reduce energy use.
Sectors and common applications
- Mining – sulphide ores, carbonates, oxides, as well as phosphates and coal
- Services – wastewater treatment
- Estimated energy savings in across the sectors was 6 PJ/pa.
|1. Energy saving potential|
|1.1 Level of energy efficiency||13.5/15|
|1.2 Market prospect||4/10|
|1.3 Energy saving potential||6/10|
|2. Technical practicality|
|2.1 Innovative or advanced nature||15/25|
|3. Economic characteristics|
|3.1 Investment per unit energy||6/10|
|3.2 Payback period||10/10|
|3.3 % of Industry $ gross added value||3/5|
|4. Social characteristics||3/5|
In Northgate Australian Ventures Corporation’s gold production process, ore is reclaimed from stockpiles and fed through a crusher and becomes feed to a semi-autogenous grinding (SAG) mill. Overflow from the SAG mill gravitates to a flotation circuit where gold-bearing sulphide minerals are concentrated. Bacteria separate the gold from the sulphide matrix using the BIOX process. The circuit contains six reactors, all fitted with motorised agitators. It was discovered that the rotational speed of the agitators could be reduced by 20% by changing their gearboxes. Savings in energy were estimated at 11 180 GJ/pa.
Due to the relative simplicity and high savings that this project generates, it was decided to implement this energy efficiency opportunity. Following metallurgical test-work to ensure minimal risk to the oxidation process, Tank 5 gearbox motor was changed from a 220 kW 4 pole motor to a 150 kW 6 pole motor, reducing the speed by 33%. It was planned to replace the 185 kW 4 pole motor on Tank 6 with a 150 kW 6 pole motor.
BM Alliance Coal Operations Pty Ltd determined their spirals-based circuit for reprocessing of flotation tailings was sub-optimal. Replacing the spirals with a state-of-the-art fluidised bed separator (Reflux Classifier) to scavenge fine tailings has improved overall plant yield.
Other companies that have identified flotation circuit optimisation as a source of energy savings can be found in the EEO opportunities register on EEX, and include:
For more information, see: