Sulfidic copper ores are too dilute for direct smelting. Smelting these materials would require too much energy and very large furnace capacities. The copper ore coming from the mine (0.5 – 1 % Cu) must be concentrated by beneficiation. The valuable minerals like chalcopyrite are intergrown with gangue. Therefore, in the first step the lumpy ore is crushed and milled into fine particles (< 100 μm) to liberate the individual mineral phases.
Copper Beneficiation Process
Typical equipment for crushing to about 20 cm are gyratory and cone crushers. Then wet grinding in semi-autogenous rod or autogenous ball mills takes place. Size classification takes is performed in cyclones. In the next step of beneficiation, valuable minerals and gangue are separated by froth flotation of the ore pulp, which exploits the different surface properties of the sulfidic copper ore and the gangue [46]. The hydrophobic sulfide particles become attached to the air bubbles, which are stirred into the pulp, rise with them to the surface of the pulp, and are skimmed off as a froth of fine concentrate. The hydrophilic gangue minerals remain in the pulp. Organic reagents with sulfurcontaining groups at their polar end, such as xanthates, are used as collectors in the flotation process. Additionally, modifiers like hydroxyl ions (pH adjustment) are used to select different sulfide minerals, for example, chalcopyrite and pyrite. Alcohols are used to stabilize the froth.
To obtain concentrates with highest possible purity and recovery rate, the flotation process usually consists of several stages which are controlled by expert systems. Various sensors for particle size, pH, density, and other properties are installed. Figure 4 gives an overview of a typical beneficiation process at a concentrator. In the first flotation stage, as much copper as possible is recovered in a rougher concentrate so that as little as possible goes to the tailings. To increase the copper recovery rate, often these tailings are leached with sulfuric acid. After regrinding, the rough concentrate is -2 of 11-cleaned in several flotation steps. After sedimentation in thickeners and filtration in automatic filter presses or vacuum filters (ceramic disk) the typical copper concentrate contains 25 – 35 % Cu and about 8 % moisture. The moisture content of the concentrate is a compromise between transporting water (cost) and avoiding dust generation during transport.
Copper concentrators typically treat up to 100 000 t of ore per day. They are located directly at the mines to achieve low transport costs. The copper recovery efficiency is over 90 %. About 95 % of the ore input goes into the tailings, which are stored in large dams near the mine and are used for water recycling to the flotation stages.
Separation of special copper ores such as those containing molybdenite or with high zinc or lead content (Canada) is also possible by flotation methods. Flotation of non-sulfide copper minerals is rare because these ores are mostly subjected to hydrometallurgical copper recovery, for example, heap leaching. In Zambia and Zaire, however, siliceous copper oxide ores are floated with fatty acid collectors, and dolomitic copper oxide ores are sulfidized with sodium hydrogensulfide and then floated
