How is it processed?

     There are two processes that are used to refine concentrated copper.  Smelting (pyrometallurgy) is used on ores with sulfides.  In smelting, the copper sinks out and the impurities rise to the top.  Air, lime, and silica are added to react with the metal oxide.  Scrap copper may be added at this point.  This new copper is known as blister copper.  This then goes through “fire refining”, where air and natural gas are blown through it to remove any sulfur and oxygen.  It is then cast into copper anodes and placed into electrolytic cells.  When it is charged, the copper collects on the cathode and is close to 99% pure. (10)

     Hydrometalurgical processes are also used.  This type of refinement is used on oxidized copper ores or wastes.  The copper is leached with sulfuric acid from the smelting process.  It is then percolated through piles of oxidized metal and collected with acid resistant liners.  It is then deposited onto crap iron in a process called cementation.  This plates the copper.  It is then refined by the pyromettalurgical process.  This is a very rare type of refining.  However, hydrometallurgical processes have many advantages over pyrometallurgical processes.  Lower grade ore can be processed, it is more energy efficient, it has lower environmental impact because waste streams are liquid and are easily contained and neutralized than sulphur dioxide gas, it has lower capital and operational costs. (10)

     Sulfur is usually fixed during the process in order to meet the Clean Air Act Standards.  This is if the sulfur content of the gas is over 4% they are made into sulfuric acid for use in refining copper further or are sold to fertilizer manufacturers.  Sometimes the metal is pretreated.  Pretreatment consistes of sorting, shredding, stripping, and magnetic separation, sweating, insulation burning, drying, flotation, and leaching.  All copper ores are concentrated.  Concentration consists of crushing the ore and passing it through screens. It is then mixed with water to create a slurry which is then fed into grinders until it is powdered.  They are processed, with the least from the highest being matte copper (35-68% Cu), blister copper (97-99% Cu), anode copper (99.5% Cu), and cathode copper by electrolytic refining (99.95%-99.96%Cu). (2)




Figure 3.1 Copper going through the pyrometallurgical refining process.
http://www.azstarnet.com/public/packages/star200/coppast.htm





Figure 3.2 A copper worker pouring the molten metal into molds.  
http://www.brass-components-india.com/copper_castings/copper_castings.htm

 

Figure 3.3 Copper cathode being inspected.
http://www.straits.com.au/default.asp?V_DOC_ID=880

 

 

Figure 3.4 A large copper leaching field.
http://www.straits.com.au/default.asp?V_DOC_ID=880

 

Relevant Sites

http://www.copper.org/education/history/g_fact_producers.html

http://www.asarco.com/AMDC/refining.html