Copper Production: From Mine to Mill Product
Copper Brought Mankind Out of the Stone Age
Copper is the first metal to have been used by mankind. More than 10,000 years ago, what’s called “native copper” was found on the surface of the Earth. This new material could be fashioned into a knife or axe much easier than stone. For nearly five millennia, copper was the only metal known.
By 5000 BC, the dawn of metallurgy had arrived and along with it the smelting of simple copper ore. By 3000 BC, silver and lead were being used and the alloying of copper with tin had begun, ushering in the Bronze Age. Brass, copper alloyed with zinc, was made as early as 500 BC. Today, pure copper and more than 400 copper alloys are used for a myriad of modern applications.
Here is a brief primer on how the copper gets from the mine to the finished product:
Sulfide and oxide ores are mined through blasting and digging and then crushed to walnut-sized pieces.
Crushed ore is ball or rod-milled in large, rotating, cylindrical machines until it becomes a powder usually containing less than 1 percent copper. Sulfide ores are moved to a concentrating stage, while oxide ores are routed to leaching tanks.
Minerals are concentrated into a slurry that is about 15% copper. Waste slag is removed. Water is recycled. Tailings (left-over earth) containing copper oxide are routed to leaching tanks or are returned to the surrounding terrain. Once copper has been concentrated it can be turned into pure copper cathode in two different ways: Leaching & electrowinning or smelting and electrolytic refining.
Several stages of melting and purifying the copper content result, successively, in matte, blister and, finally, 99% pure copper anodes .Sulfur is captured and converted to a sulfuric acid by-product to eliminate air pollution .Reclaimed scrap copper may be resmelted at this stage.
Anodes cast from the nearly pure copper are immersed in an acid bath. Pure copper ions migrate electrolytically from the anodes to “starter sheets” made from pure copper foil where they deposit and build up into a 300-pound cathode. Gold, silver and platinum may be recovered from the used bath.
Pure Copper Cathodes
Cathodes of 99.98% purity are shipped as melting stock to mills or foundries for use along with high quality scrap materials. There they are cast and rolled into wire rod, or cast into billets, cakes or ingots as pure copper or alloyed with other metals.
Coiled rod about ½” in diameter is drawn down by wire mills to make pure copper wire of all gauges.
30” logs, about 8” in diameter, of pure copper or of copper alloys are sawed into shorter lengths which are extruded and then drawn as tube, rod and bar stock of various sizes and shapes. Rod stock may be used for forging.
Slabs of pure copper or of copper alloys, generally about 8” thick and up to 28’ long, may be hot- and cold-rolled to produce plate, sheet, strip and foil.
Bricks of pure copper or of copper alloys may be used by mills for alloying with other metals or used by foundries for casting.