Copper, Molybdenum & Gold
Copper & Molybdenum
The most common forms of copper ore are copper oxide and copper sulfide. The initial processing stages for both types include
mining and transportation, followed by crushing, usually performed near or within the mining pit.
For copper sulfide ores, crushed material undergoes wet milling to liberate copper minerals. The resulting ore slurry is then subjected to froth flotation, where chemical reagents (collectors and frothers) and controlled pH conditions cause copper minerals to attach to air bubbles and float. The copper-rich froth is skimmed off, while the gangue settles as tailings.
The copper concentrate is subsequently thickened and filtered, producing a final concentrate containing approximately 30% copper along with other metals. This concentrate is sent to a smelter, where high temperatures further purify the copper, followed by electrolysis to achieve 99.99% purity.
Copper and molybdenum commonly occur together as sulfide minerals in ore deposits worldwide. Although molybdenum is mined directly in some primary operations, a large share of its production comes as a by-product of copper mining. During flotation processing of copper ores, both copper and molybdenum are enriched in the froth concentrate. To separate and upgrade molybdenite, selective flotation is typically applied after depressing copper and iron sulfides.
Oxide ores are primarily processed via hydrometallurgical methods using water-based solutions at ambient temperatures. The typical process involves heap leaching, solvent extraction, and electrowinning to extract and purify copper.
Gold
Gold is a chemically inert element often found in its native form as nuggets or grains within rocks and veins. The processing method depends on the ore type and may include gravity separation, flotation, amalgamation, cyanide leaching, resin-in-pulp, carbon paste adsorption, and heap leaching.
For finely disseminated gold, cyanidation is the primary extraction method. Common processing approaches include:
Flotation followed by leaching of the concentrate
Flotation and leaching of sulfide-free flotation tails
Gravity concentration combined with flotation and leaching
Heap leaching after coarse crushing
Whole ore cyanidation
Cyanidation works by dissolving fine particles of metallic gold and silver in dilute sodium cyanide (NaCN) solutions, while leaving most other minerals unaffected. The gold-cyanide complex is then adsorbed onto activated carbon, from which gold is stripped using an eluant solution. Finally, electrowinning deposits metallic gold onto electrodes, producing high-purity gold.