Description / Application
Individual cathode sheets are manufactured to different dimensions by different suppliers in the range of 0,5 m2 to 1 m2 and 3 to 20 mm thick, with or without ‘ears’. Copper cathode is the primary raw material input for the production of copper rod for the wire and cable industry. Copper is also used in the production of brass, copper tube, copper sheet products, and found in over 450 alloys.
Copper cathodes are used as a raw material feed for the production of high purity copper and copper alloy products. It is therefore essential that, during shipping and transportation, they are not contaminated with any extraneous materials.
Copper Production from Ore to Finished Product
From its original home buried underground in a mine to its use in a finished product such as wire or pipe, copper passes through a number of stages. When it is recycled it can pass through some over and over again. Below is a quick description of the path.
1. Mining, Crushing
The beginning for all copper is to mine sulfide and oxide ores through digging or blasting and then crushing it 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.
Oxide ore and tailings are leached by a weak acid solution, producing a weak copper sulfate solution.
5a. Electrowinning (SX/EW)
The copper-laden solution is treated and transferred to an electrolytic process tank. When electrically charged, pure copper ions migrate directly from the solution to starter cathodes made from pure copper foil. Precious metals can be extracted from the solution.
Several stages of melting and purifying the copper content result, successively, in matte, blister and, finally, 99% pure copper. Recycled copper begins its journey to finding another use by being resmelted.
5b. Electrolytic Refining
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.
6. Pure Copper Cathodes
Cathodes of 99.9% purity may be shipped as melting stock to mills or foundries. Cathodes may also be cast into wire rod, billets, cakes or ingots, generally, as pure copper or alloyed with other metals.
7. Cathode is converted into:
Wire Rod – Coiled rod about 1/2″ in diameter is drawn down by wire mills to make pure copper wire of all gages.
Billet – 30′ logs, about 8″ diameter, of pure copper are sawed into these shorter lengths which are extruded and then drawn as tube, rod and bar stock of many varied sizes and shapes. Rod stock may be used for forging.
Cake – Slabs of pure copper, generally about 8″ thick and up to 28′ long, may be hot- and cold-rolled to produce plate, sheet, strip and foil.
Ingot – Bricks of pure copper may be used by mills for alloying with other metals or used by foundries for casting.
Shipment / Storage / Risk factors
Bundles of cathode sheets of between 1 and 4 tonnes and held together by steel strapping are shipped unpackaged. Care should be exercised during handling to avoid straps breaking which cause the bundles to become unstable with potential separation and loss of some sheets.
Electrolytic copper cathodes are usually bought upon a weight basis, and are normally shipped unpacked, often bound together with metal bands. During handling of bundled cathodes, care should be taken that rough handling does not cause breakage of metal bands.
It is quite common for cathodes to have surface excrescences arising out of the process of manufacture, in the nature of small ‘pimples or warts’. Handling in the course of transit may result in these surface irregularities being broken down and the cathodes delivered with a smooth surface. This may result in a difference between shipped and delivered weights. Cathodes are manufactured with ‘ears’ for hanging purposes and frequently these ‘ears’ are knocked off, resulting in further loss of weight.
When over-stowed, care should be taken that other cargo does not cause deleterious contamination of the copper.