The Copper Concentrator at Mt Isa Mines experiences periodic problems with final concentrate dilution by naturally hydrophobic minerals. The preflotation stage does not have enough residence time to remove all the naturally hydrophobic minerals, such as talc and carbonaceous pyrite, from the feed. A final concentrate of less than 2% MgO is required for treatment by the Copper Smelter. Future ore sources contain much higher talc grades, that will not be treatable with the current flotation circuit. This thesis aims to quantify the chalcopyrite losses and potential grade improvement associated with the reverse flotation of talc and carbonaceous pyrite from a chalcopyrite concentrate.
To remove the naturally hydrophobic minerals from the final chalcopyrite concentrate, the chalcopyrite must be depressed. The following hypotheses were developed during the literature review:
1. Adjusting the pH to above 11 will disrupt the surface and depress the chalcopyrite while allowing the naturally hydrophobic minerals to float.
2. Adjusting the Eh to below -100mV will cause the collector to desorp from the chalcopyrite resulting in its depression whilst allowing the naturally hydrophobic minerals to float.
3. Chalcopyrite may be depressed by adding sodium sulphide to destroy or displace collector from the chalcopyrite surfaces.
4. Chalcopyrite may be depressed by adding sodium hydrosulphide to destroy or displace collector from the chalcopyrite surfaces.
The above hypotheses were tested using laboratory scale flotation tests. The first hypothesis was tested by varying pH during flotation of a final concentrate between pH11 and pH12.5. The second was tested through reverse flotation tests at varying electrochemical potentials using sodium dithionite. Finally, varying depressant addition rates that corresponded to variations in electrochemical potential were tested.
All the hypotheses were proven to be true. However, only reverse flotation by sodium sulphide and sodium hydrosulphide were found to be feasible.
Reverse flotation using sodium sulphide had superior metallurgical performance to both reverse flotation using sodium hydrosulphide and preflotation. Reasonable separation was achieved for electrochemical potentials less than 0mV, which is equivalent to 40 grams of sodium sulphide per tonne of flotation feed. To maintain these reducing conditions, nitrogen is required as the flotation gas.