As one of the great metals of commerce, it is not surprising that copper released by humans into the environment is in significant excess over what might be found naturally. Copper (and other) pollution has occurred in the vicinity of copper mines and smelting operations since mankind began the activity several millennia ago. The excavation of Cu-containing earth at open pit copper mines can produce copper rich dusts which are spread in the wind around the mine site. Most of these ores are sulfide minerals, and oxidize in the air to sulfates, producing sulfuric acid, which renders the copper in the mineral highly soluble. The same process occurs when mine tailings (the low-grade material removed from the mine but not sent for smelting) sit in the open. Freshly exposed to air and water, sulfide minerals oxidize, producing sulfuric acid, resulting in metal rich acid mine drainage. This acidic, contaminated water can drain into surface streams or into the ground, contaminating aquifers. Since the Clean Air and Clean Water Acts have been implemented in the US, pollution from these sources has been substantially reduced, but not eliminated. Similar processes occur at mines other than copper mines where Cu may not be the element of primary interest, but occurs in elevated concentrations (Zn, As, Ni, Pb etc.). Pollution control methods include dust abatement, lining tailing dumps with impervious liners, chemically treating the waters discharged from the mine, and recycling the captured materials into the product stream.
Refining of copper (both pyro- and electrometallurgi-cally) can be a significant source of pollution. In smelting, the heating of the ore to drive off the sulfides and reduce the copper to its elemental state releases a variety of compounds, including copper, sulfur dioxide, arsenic, cadmium, lead, mercury, and zinc to the air and waste water. In modern operations in the US, much of the pollution is captured by scrubbers and water treatment plants. For example, much of the sulfur dioxide can be captured as sulfuric acid and sold as a by-product. However, before the invention and implementation of the controls on air pollution, many smelting sites produced wide swaths ofpolluted land with both sulfur and metals. Outside the more developed countries, this is still a common practice.
While leaching and electrorefining doesn't have the potential to produce the large amounts of air pollution that smelting does, the large amounts of caustic and toxic chemicals used in the process present ample opportunity for water and soil pollution. Again, in developed countries, these wastes are largely, but not entirely, controlled.
There are many other significant sources of copper pollution. These include burning of fossil fuels, particularly coal, which releases copper in both fly and bottom ash, industrial incinerators, used motor oils, city water treatment sludge, sewage, and sewage sludge and so on. The copper in copper plumbing dissolves slowly and adds copper to the water supply and waste stream, copper roofs leach copper when exposed to acidic rain, and brake pads of modern cars contain copper which wears away over the course of use. The condensers in some power plants use Cu/Ni alloys as heat exchangers; fouling resistance is a bonus.
Copper has a long history of being used as a pesticide or fungicide, and is often released to the environment for that purpose. Paris green, (copper acetoarsenate), originally used as a wall paper pigment, was adopted as a pesticide in the 1860s. 'Bordeaux mix' (copper sulfate and lime) is still used to control fungus on grapes and other crops. It was originally adopted in France in the 1880s to prevent grape theft by making consumers of unwashed grapes ill, but proved effective against mildew. The hulls of some wooden ships were clad with copper sheeting after the mid-1700s to inhibit fouling and invasion by ship worms, Teredo sp. (actually wood burrowing clams). Some vessels are currently built with Cu/Ni alloy hulls, which save considerable maintenance compared to a steel hull due to inhibition of fouling. Copper-based anti-fouling paints have been used to inhibit fouling on boats for several centuries, and are still in wide use. Copper in several forms (including copper napthenate, chromated copper arsenate, copper chromium fluoride, ammoniacal copper zinc arsenate, ammoniacal copper quat, and copper-8-hydroxyquinolinate) has long been used to preserve wood from insects and decay. Copper sulfate is sometimes used to inhibit algae growth in lakes and ponds. In short, many potential sources of copper pollution exist, and have existed since mankind began to mine and refine it.
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