Copper sulfide represents the main source of produced copper. The three main types of copper sulfide deposits are high grade massive and disseminated copper-porphyritic and copper-bearing sandstone. Unlike the copper sulfide deposits presented by massive ores, copper-porphyritic deposits contain only 5-10% of the ore minerals, mainly represented by chalcopyrite, pyrite, bornite, tennantite, and molybdenite. These minerals are spread throughout the rock as separate grains – ‘porphyritic’ nodules and thin veinlets. The usual grades for such polymetallic ore types are 0.3-0.6% copper, 0.1-0.2% zinc, and 0.1-0.01% molybdenum.
The porphyritic ore features the tight intergrowth of sulfide minerals, and different sizes of sulfide minerals tend to show up. Based on this material composition, bulk sulfide flotation with further regrind and cleaning steps will be used to process such ores. Pyrite occurs commonly with copper sulfides, while pyrrhotite occurs less often. Nonmetallic minerals encountered most often are quartz, silicates, sericite and barite.
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All copper sulfides are processed through flotation using xanthates at 6-12 pH. When pH values are lower, it is better to use aeroflot-type reagents instead of xanthogenates. If molybdenite flotation is required to separate it from copper sulfides, the pH should be no more than 11 to provide pyrite depression, and lime is added with a small amount of cyanide and soluble silica is used to suppress gangue minerals within the molybdenum flotation circuit.
The molybdenum recovery from bulk copper-molybdenum concentrate might use the following method:
• Copper-molybdenum concentrate treatment with sodium sulfide. In this case, the copper sulfides and other sulfides are suppressed and the molybdenite could be recovered by flotation with non-polar (hydrocarbonic) collectors.
• Oxidative steaming of (copper-molybdenum concentrate) with lime. In this case the chalcopyrite and pyrite lose their adsorptive surfaces, oxidize and sorb suppressing calcium ions. The thickening that is carried out to remove excessive lime is followed by molybdenite flotation with multiple cleaning stages, adding sodium sulfide at higher temperatures.
The number of flotation stages in both copper and molybdenum circuits depends on the content of the respective materials within the feed, and their grades in the final products.
After thickening, filtration and drying, the concentrates are shipped to the smelter for further processing.
This is a conventional method of copper-molybdenum processing. The use of more efficient flotation reagents could make the process cheaper by reducing the number of flotation cycles; then projects with marginal copper and molybdenum grade ore might be developed with the improved process economics.
The metal price dictates the respective strategies that companies choose for project implementation and production optimisation. Mineser takes an active role in implementing such projects.