|Infobox on Copper Concentrates|
|Example of Copper Concentrates|
|Stowage factor (in m3/t)||0,45 m3/t (bulk)|
|Humidity / moisture||-|
|Risk factors||See text|
Copper extraction techniques refers to the methods for obtaining copper from its ores. This conversion consists of a series of chemical, physical, and electrochemical processes. Methods have evolved and vary with country depending on the ore source, local environmental regulations, and other factors.
As in all mining operations, the ore must usually be beneficiated (concentrated). To do this, the ore is crushed then it must be roasted to convert sulfides to oxides, which are smelted to produce matte. Finally, it undergoes various refining processes, the final one being electrolysis. For economic and environmental reasons, many of the byproducts of extraction are reclaimed. Sulfur dioxide gas, for example, is captured and turned into sulfuric acid — which is then used in the extraction process.
Most copper ores contain only a small percentage of copper metal bound up within valuable ore minerals, with the remainder of the ore being unwanted rock or gangue minerals, typically silicate minerals or oxide minerals for which there is often no value. The average grade of copper ores in the 21st century is below 0.6% copper, with a proportion of economic ore minerals (including copper) being less than 2% of the total volume of the ore rock. A key objective in the metallurgical treatment of any ore is the separation of ore minerals from gangue minerals within the rock.
The first stage of any process within a metallurgical treatment circuit is accurate grinding or comminution, where the rock is crushed to produce small particles (<100 μm) consisting of individual mineral phases. These particles are then separated to remove gangue, thereafter followed by a process of physical liberation of the ore minerals from the rock. The process of liberation of copper ores depends upon whether they are oxide or sulfide ores.
Subsequent steps depend on the nature of the ore containing the copper. For oxide ores, a hydrometallurgical liberation process is normally undertaken, which uses the soluble nature of the ore minerals to the advantage of the metallurgical treatment plant. For sulfide ores, both secondary (supergene) and primary (unweathered), froth flotation is used to physically separate ore from gangue. For special native copper bearing ore bodies or sections of ore bodies rich in supergen native copper, this mineral can be recovered by a simple gravity circuit.
Copper concentrate is the first commercial product of the copper production line and is composed of approximately equal parts of copper, iron and sulfide. Concentrates are the raw material for all copper smelters, which by processing it obtain an impure form of metallic copper, anode or blister copper, which is later used to produce high purity refined copper. The production of concentrates implies the crushing and later milling of the ore down to a particle size allows releasing copper by flotation. The concentrates from different regions have approximately between 24% up to 36% of copper. Copper concentrates are then submitted to a final filtration and drying process to decrease the humidity to 8-9%.
Mainly copper goes through different stages and degrees of refinement, to a lesser extent the byproducts such as molybdenum, sulfuric acid and precious metals that come with copper in the ore.
- Mining and Crushing
- Leaching or Smelting
- SX/EW or Electro Refining
Copper is processed in several stages from extraction and crushing of the ore to electrolytic refining, which allows obtaining 99.99% pure Copper Cathodes.
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.
The first commercial copper product, in an increasing chain of added value, is the copper concentrate, which main components are copper, iron and sulfide. During the same processing stage molybdenum, as bi-sulfide, is obtained, which is then processed to attain the commercial form of molybdenum trioxide.
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 methods:
- Leaching & Electro-Winning
- Smelting & Electrolytic Refining
Copper concentrate is smelted and converted to metallic copper, which allows it to attain forms that can be submitted to further refining, more than 99% pure, as in copper anode and copper blister. The main application of copper anode is to use it as raw material in the process of electrolytic refining, to produce the electrolytic refined cathode, purity 99.99%.
Leaching & Electro-Winning Method
Oxide ore and tailings are leached by a weak acid solution, producing a weak Copper Sulfate solution.
B. Electro-Winning (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.
Smelting & Electrolytic Refining Method
A. Smelting 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 re-smelted.
B. Electrolytic Refining
Anodes cast from the nearly pure copper is immersed in an acid bath. Pure copper ions migrate electrolytically from the anodes to "starter sheets" made from pure copper foil or steel where they deposit and build up into a refined copper cathode. During this process, gold, silver and platinum may be recovered from the used electrolytic bath.
After smelting and conversion process, through a treatment of metallurgical gas generation that gives rise to other by-products which are the sulfuric acid and the anodic slimes which are rich in silver and gold.
Copper Standards & Types
In the chain of the copper industry, mining companies extract the ore from the deposits and process it to obtain a metal of high purity that is sold to its main clients, the fabricators of semi-manufactured products, which in turn will transform it to then offer it to the end consumers.
Electrolytic copper cathodes are produced under several grades along with off-grades used for low conductivity appliances and alloys. Cathodes mainly consist of 4 different qualities; LME registered high grade, non registered high grade, standard grade and off-grade. LME registered copper refineries manufacture LME registered High (A) Grade cathodes along with Non-LME registered High (A) grade cathodes, Standard Grade cathodes and off-grade cathodes.
According to LME copper contract specifications, cathode's sulfur ratio shall not exceed 15ppm in order to be able to be applicable for LME designated standards. In certain regions copper refineries may produce their LME registered high grade cathodes with a sulfur ratio of <8ppm where they also produce Non-LME registered high (A) grade cathodes with a ratio of 8 ppm that is within the range of LME designated standards but not LME registered. Some refineries produce standard grade cathodes with a ratio of 15ppm that is still within the LME designated high (A) grade cathode quality.
The chemical specification for electrolytic grade copper is ASTM B 115-00 and BS:EN 1978:2000. Registered cathodes of 99.99% purity are supplied along with designated marks and LME registration certificates. They are shipped as melting stock to copper mills or foundries to be cast into wire rod, billets, cakes or ingots, generally, as pure copper or alloyed with other metals.
Shipment / Storage
When copper concentrate has been packed in properly closed drums it can be stowed on deck or below deck, and in this case it will not be necessary to take special precautionary measures.
In order to counter possible temperature increases bagged copper concentrate (also if lined with plastic inner bags) should be stowed with internal ventilation ducts in ventilated containers. Containers with copper concentrate (in jute bags) may only be stowed in accessible locations. During the voyage temperatures in this cargo to be taken daily. If the temperature within the container is higher than outside forced ventilation is to be applied.
Stuffing possibly carried out under supervision of a cargo surveyor. This person also has to determine the moisture content. The cargo surveyor shall have to submit a survey report of which the ship must receive copy before departure. Metal surfaces contaminated with copper concentrates can be cleaned by rust cleaner (32% Phosphoric Acid).
For bulk shipments, see Risk factors. See also Mineral concentrates.
Check the applicable MSDS sheet and IMSBC Code (Mineral concentrates; Section 4: Assessment of acceptability of consignments for safe shipment to which shippers/producers' attention should be drawn. If in any doubt Section 8: Cargoes which may liquefy (test procedures) should be consulted and on board testing carried out).