Two basic production processes are used to produce pure copper from copper ore: smelting and solvent extractionelectrowinning (SX-EW).
Ore is mined with less than 1 percent copper content. It is then concentrated at the mining site into a concentrate having approximately 20 percent copper. Also included in the concentrate are sulfur, iron, and a number of impurities that are hazardous air pollutants (HAPs), including arsenic, lead, cadmium, cobalt, manganese, nickel, selenium, antimony, beryllium, and mercury. Copper concentrate is the input to the smelting process.
Under the traditional smelting process, the concentrate is shipped to the smelter, blended, dried, and fed to the smelting furnace. Both slag and matte copper are tapped from the bottom of the furnace every few hours. The slag is disposed of and the matte copper (now typically over 50 percent copper) is charged to the converters. The converter operation continues to remove sulfur, iron, and other impurities and produces blister copper, which is at least 95 percent copper.
The blister copper is charged to the anode furnaces, where further refinement takes place. The anode copper, now 99.5 percent pure copper, is cast in copper anodes. Copper anodes are the output of the smelting process. SX-EW is an alternative method of producing purified copper from oxidized ores.
In this process, a solution of sulfuric acid is poured over the copper concentrate, leaching the copper out of it. Then electrically charged pure copper ions are attracted out of the solution to a charged copper cathode. Currently, approximately 30 percent of copper is produced using SX-EW; the rest is produced using the traditional smelting process. The copper anodes are then taken to an electrolytic refining plant, where 99.99 percent commercial grade copper is produced. The Primary Copper Smelting NESHAP includes only the smelting operations and does not include the mining, concentrating, or electrolytic refining operations.
Major By-Products, Co-Products & Substitution Possibilities
The copper smelting process generates slag (waste materials remaining after the copper is concentrated and converted). In addition, smelters generate air emissions.
The HAPs emitted from primary copper smelters consist primarily (approximately 80 percent by mass) of compounds of lead and arsenic.
Other metallic HAP emissions include compounds of antimony, beryllium, cadmium, chromium, cobalt, manganese, mercury, nickel, and selenium. Sulfur dioxide is another by-product or co-product of the smelting process. The sulfur dioxide is captured and converted to sulfuric acid at all the smelters in co-located acid plants.
Input substitution possibilities are limited. Scrap copper can be substituted for the matte copper in charging the converter. In addition, another production process, SX-EW can be substituted for the traditional smelting process for oxide ores and secondary sulfide ores. It is not suitable for primary sulfide ores, however, which predominate in many U.S. mines.
Charts below dated November 1997:
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Text Source: EPA Draft Report, "Economic Impacts of Air Emission Standards: Primary Copper Smelting," Prepared by Katherine B. Heller and Jean L. Domanico, Research Triangle Institute Center for Economics Research, November 1997. [full report]
