Professor Christina Cogdell
11 December 2014
The U.S. One Cent Coin: Raw Materials
The penny is the first coin minted in the United States (A Brief History of the U.S. Cent). This coin, known as the Fugio cent, was made of 100% copper and designed by Benjamin Franklin in 1787(McMorrow-Hernandez). In 1793 the U.S. Mint began minting the U.S. one cent coin (A Brief History of the U.S. Cent). The coin was much larger than the current penny, almost the size of the half dollar, and heavy; the weight of the coin was directly related to the value of the copper it consisted of (Cents). 1815 was the only year no one cent coins were minted due to a copper shortage caused by the War of 1812 (A Brief History of the U.S. Cent). The price of copper was rising in the 1850’s and a smaller cent was developed. This penny consisted of 88% copper and 12% nickel (Cents). The one cent coin went through another composition change after the Civil War in 1864 to 95% copper and 5% zinc (A Brief History of the U.S. Cent). In 1943 the copper was completely removed and replaced with steel do to World War II; copper was reintroduced back into the penny in 1944. In 1982 the composition changed yet again; the penny became primarily zinc with a thin copper plating (McMorrow-Hernandez). Today our pennies consist of 97.5% zinc and 2.5% copper and cost 1.83 cents to create.
The U.S. one cent coin has had a wonderful history and many composition changes since its creation in 1787. In today’s modern world the penny has no relevance and is too expensive to manufacture. The penny is often discarded in our society, the leave a penny tray is a great example. The cost of a current U.S. one cent coin is 1.83 cents but the value is still only 1 cent. This is directly related to the materials cost (CC Enterprises LLC). The costs of the raw materials are too great to keep the U.S. one cent coin in production.
The two main raw materials in the current US one cent coin are zinc at 97.5% and copper at 2.5%. Neither zinc nor copper occur as pure minerals in nature. Zinc is most commonly derived from sphalerite which is a zinc sulfide. Zinc is the fourth most important metal in the world, as far as quantity produced; following iron, aluminum, and copper (Sibley). Extraction and concentration requires great energy and processing to acquire the valuable metal. The zinc used in the U.S. one cent coin comes from the Tennessee Valley Mines; this mine group is comprised of 6 mines: Young, Immel, Coy, Elmwood, Gordonsville, and Cumberland (Smelting and Alloying). These zinc mines are underground drill and blast mines. “Scalers”, large underground vehicles, are also used to knockdown loose rock from mine walls (Knoxville News Sentinel). The mineral content in the rock from these mines only contain 3-11% of zinc (Metallurgical Industry). Despite the high energy needed to extract the mineral from the surrounding rock, the value of the mineral is very profitable. (International Precious Metals Institute). The boulders and rocks that are drilled, blasted, and scaled from the walls are then sent through a concentration process which occurs onsite of each of these mines.
The concentration process begins by crushing and grinding the boulders and rocks until they are almost a fine power (International Precious Metals Institute). Once the ore has been reduced to a fine powder they are put through a froth flotation process. The froth flotation process separates the zinc sulfide from the rest of the ore. The froth flotation is divided up into cells, which usually cascade onto each other to further concentrate the zinc. Each cell is filled with water, ground ore, and collector chemicals such as xamthates, dithiophosphates, and/ or thionocarbamates (Orcia). The collector chemicals are a very small portion of the mixture. These chemicals attach to the zinc sulfides to make them hydrophobic, or to have little or no affinity for water (dictionary.com). Frothing agents such as MIBC and DSF specialty range are added to the slurry and air is then released from the bottom of the cell. The zinc sulfides, now hydrophobic, attach to the bubbles and rise to the surface of the slurry to the top to create froth. The zinc sulfide froth overfills from the top of this cell into the next cell. This process is repeated multiple times until the resulting froth is thick and containing 62-65% zinc concentrate (Nyrstar Tennessee Mines). Once the zinc is concentrated at the mine it is transported to the smelter.
The distance the zinc concentrate travels from mine to smelter is relatively small. Young, Immel, and Coy mines are located within 20 miles of each other and are about 250 miles from the smelter. Elmwood, Gordonsville, and Cumberland mines are all located within 10 miles of each other and are about 100 miles from that the same smelter in Clarksville, TN (Nyrstar Tennessee Mines). This smelter is Nyrstar, and it is utilized by Jarden Zinc; the manufacturer of the penny blanks. The first step is to remove the remaining sulfides from the zinc concentrate.
The first step is to roast the zinc concentrate; this removes the sulfide from the zinc. The fluidized-bed roaster roasts the zinc concentrate under pressure; the pressure amounts to a little less than the atmospheric pressure. The zinc concentrate is “suspended and oxidized in a feedstock bed supported on an air column.” (Metallurgical Industry). The average temperature to heat the concentrate is around 1000°C. The chemical process that takes place in the roaster is the conversion of zinc sulfide to a zinc oxide.
2ZnS + 30₂ → 2ZnO + S0₂
2SO₂ + O₂ → 2SO₃
The result is an impure zinc oxide, or calcine, and sulfuric acid. The sulfuric acid from this process is very important and is used at another stage for the zinc processing. Once the roasting is complete the electrolytic process can begin (Metallurgical Industry).
Electrolytic processing, a hydrometallurgical process, is the next step for the zinc. This process includes leaching, purification, and electrolysis (Metallurgical Industry). Leaching utilizes the sulfuric acid created from the zinc roasting process. An aqueous solution of sulfuric acid, zinc oxide, and spent electrolytes is created (Zinc Environmental Profile). The zinc is dissolved in this process leaving behind iron, lead, and silver (Zinc Production). A few other impurities can also be dissolved with the zinc and so the leach solution undergoes a purification process. Purifying additives, undisclosed, are added to the leach solution and the solution temperature ranges from 40-85°C. The resulting solution is a zinc sulfate solution and it limits impurities to less than 0.05 milligram per liter. The next step of the electrolytic process is the electrolysis; metallic zinc is recovered from the purified solution in this step (Metallurgical Industry). A current is passed between a lead alloy anode and an aluminum cathode submerged in the circulating purified zinc sulfate solution. This current ranges between 3.3-3.5 volts and causes the high purity zinc to deposit on the cathode (Zinc Production). The cathode is then removed from the solution to recover the deposited zinc every 24-48 hours (Metallurgical Industry). This zinc is removed, dried, and then melted. The resulting melted zinc is cast into Special High Grade (SHG) zinc ingots consisting of 99.995% zinc (Smelting and Alloying). The current U.S. one cent coin also contains copper which has to be first extracted.
In nature copper is found as native, oxide, or sulfide. Copper sulfide, or chalcophile, is the most plentiful (Morin, 1). Copper is the third most industrial metal following iron and aluminum (US Geological Survey). The mine that Jarden Zinc, the producers of the penny blanks, receives its copper from remains undiscovered and as so the extraction of copper will be based off of the extraction and leaching methods of Morenci mine in Arizona.
The Morenci mine is the largest producer of copper in the United States; in 2013 it produced 664 million pounds of copper alone (Niemuth). The ore content at Morenci mine is a predominantly oxide copper mineral called chrysocolla. There is also chalcopyrite and chalcocite; these are the primary and secondary copper sulfides. The ore is mined exclusively for leaching at Morenci mine. Morenci mine is an open-pit copper mine located about 50 miles northeast of Safford, AZ (Freeport McMoRan). All copper produced from Morenci mine is in the form of copper cathodes that are 99.99% pure copper (Dresher). The mine extracts copper by blasting the copper bearing rock and excavating the blasted rock with large shovels. The blasted rock can contain as little as .5% copper. The blasted rock is shoveled into a truck and is hauled to the specialized leaching area on the property (ASARCO).
The Morenci mine employs a bacteria leaching process known as solvent extraction /electrowinning (SX/EW) to oxidize the copper sulfides. The bacteria used are native to the site and it oxidizes the copper sulfides to create ferric sulfate and sulfuric acid. The leaching process occurs in two large piles of crushed ore that are saturated with sulfuric acid. The sulfuric acid dissolves the copper and the copper solution is recovered from the bottom of the piles. The copper is extracted from the solution in a solvent extraction process. This is done by using and organic extractant which exchanges the copper for hydrogen in the solution. The remaining solution is returned to the leaching piles as an acidic solution. Depleted electrolyte is used to strip the copper from the organic extractant. The remaining copper aqueous solution is pumped to the tank house where the electrowinning process occurs (Dresher). Electrowinning involves sending an electric current between an anode and cathode submerged in the copper electrolyte solution; during this process the copper from the solution deposits on the cathode (Freeport McMoRan Inc.). As the electrolyte is depleted of copper it becomes acidified. This can then be pumped back to the solvent extraction stage and used again as the primary source of acid for the leaching (Dresher). The resulting copper from this process is 99.99% pure and ready to ship to Jarden Zinc to become the U.S. one cent coin blank.
Jarden Zinc is located in Greensville, TN (Jarden Zinc Products). The zinc ingots travel 294 miles from Clarksville, TN and the copper cathodes travel 1,775 miles from Morenci, AZ to Jarden Zinc. Although Jarden Zinc does not outline their coin blanking process in detail, the U.S. Mint and other sites do cover the general coin making process. First step in making the blank coins is to mold the zinc in the appropriate size and shape.
The zinc is cast from the melted zinc ingots into continuous bars 1.5 inches thick by 5 inches wide. Then the bar is cut about 30 inches long. These bars of zinc then go through a roughing mill, where rollers press the bar flat with up to nine tons of force. The bars go through this stage about a dozen times until the bar is a half inch thick strip (How It’s Made). The resulting strip is fed through the finishing mill; the strip is thinned down to its final thickness of 1.55mm (Enchanted Learning). The zinc strip next enters the blanking machine that cuts the circular disks that will become the penny. The rimming or upsetting machine is where the raised edge or rim is added to the penny (How It’s Made). The spinning wheel in the rimming machine forces the blanks along a stationary segment; this force causes the edge to slightly rise. The coin blanks are called “coin planchets” officially once it has a rim (Unser). The planchets are led into a tub where they will be washed with water and a cleaning solution (How It’s Made). The cleaning solution recommended is a mild alkaline (Jarden Zinc Products). Steel beads are added to the wash and act as an abrasive agent, smoothing and polishing the coin planchets. After the 20 minute wash cycle the tub empties into a shifter that separates out the steel beads; the planchets are then dried (How It’s Made). Copper is electroplated onto the zinc using Jarden’s oblique barrel plating line; this ensures that the copper plating covers the entire planchet including the rim (Jarden Zinc Products). The penny planchets are now ready to be shipped to the U.S. Mint for minting.
The U.S. one cent coin is the only coin whose coin blank, or planchet, is brought in and not produced at the U.S. Mint. The penny planchets now travel from Jarden Zinc in Greeneville, TN to either Philadelphia, PA 566 miles or Denver, CO 1,401 miles away. They are shipped in pallets that contain about 400 thousand coin planchets each and weigh almost a ton. The pallets are emptied onto conveyer belts and fed along the minting process (60 Minutes). The penny planchets are then taken to the press where there is a mounted reverse and obverse die. The coins are pressed by a striker that consists of two dies; the reverse or “tails side” die is stationary while the obverse or “heads side” die is the hammer. Thirty five tons of pressure is used to transfer the design of the dies to the penny (Unser). 700 pennies are pressed per minute, which means 12 pennies are pressed per second (60 Minutes). After the pennies are pressed they fall into a trap and wait for inspection. Once they pass inspection they are counted, weighted, bagged, and then stored in a vault. The pennies are eventually shipped out to Federal Reserve Banks across the nation to enter into circulation (Unser).
There are twelve Federal Reserve Banks in the country. They are located in: San Francisco, CA, Dallas, TX, Kansas City, MO, Minneapolis, MN, Saint Louis, MO, Chicago, IL, Atlanta, GA, Richmond, VA, Cleveland, OH, Philadelphia, PA, New York, NY, and Boston, MA (FRB). The furthest a newly minted penny can travel from the Philadelphia mint is 2,875 miles to the San Francisco Federal Reserve in California. The furthest reserve from the Denver mint is 1,972 miles to the Boston Federal Reserve in Massachusetts. Once the coins arrive at the Federal Reserve individual banks can purchase the new currency for circulation. From there the penny lives out its lifecycle. The average penny life cycle is 25 years (Jarden Zinc Products). At the end of the penny’s life cycle banks return the coins the Federal Reserve. The coins are destroyed and melted (McMorrow-Hernandez).
The U.S. penny has been around since 1787. It has changed in size and composition to keep up cost of the raw materials as well as with demand. Currently the U.S. one cent coin cost 1.83 cents but only has the value of one cent. The demand is no longer prevalent either; many people do not bother to keep their pennies. The cost of the two main raw materials, zinc and copper, have exceeded the value of the one cent coin and therefore the U.S. one cent coin should be discontinued from production.
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ASARCO. "Makng Copper." ASARCO. ASARCO Grupo Mexico, 2013. Web. 4 Dec. 2014. <http%3A%2F%2Fwww.asarco.com%2Fabout-us%2Four-locations%2Fasarco-mineral-discovery-center%2Fmaking-copper%2F>.
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Freeport McMoRan Inc. "Electrowinning." Electrowinning. FCX Freeport-McMoRan Inc., 15 Aug. 2014. Web. 04 Dec. 2014. <http://www.fcx.com/resources/fmi/electro.html>.
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Knoxville News Sentinel. "Knowsy Knoxville: Nyrstar's Immel Mine and Young M." YouTube. YouTube, 27 July 2010. Web. 04 Dec. 2014. <https://www.youtube.com/watch?v=oaFMh9kJu1E>.
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Jarden Zinc Products. "About Jarden Zinc." About Jarden Zinc (n.d.): n. pag. Jarden Zinc Products. Jarden Zinc Products, 19 Feb. 2013. Web. 04 Dec. 2014. <http://jardenzinc.com/techdata/Jarden-Zinc-Product-Guide.pdf>.
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McMorrow-Hernandez, Joshua. "The Amazing And Colorful History Of The U.S. Penny." US Coins. Fun Times Guide, n.d. Web. 27 Nov. 2014. <http://coins.thefuntimesguide.com/2010/02/us_penny.php>.
McMorrow-Hernandez, Joshua. "What's The Lifespan Of A Coin? Find Out How Long Coins Last | The Fun Times Guide to U.S. Coins." US Coins. Fun Times Guide, Mar. 2013. Web. 05 Dec. 2014.
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Professor Christina Cogdell
Embodied Energy and Inefficiency in the Lifecycle of the US Penny
In recent years, the US penny has come under much scrutiny. The penny has been more expensive to mint than its face value of one cent since 2006, when it cost 1.119 cents to produce (“Cost to Make a Penny: Chart/Graph”). Over time, Americans have grown less attached to the penny as well (“Penny Worth Saving, Say Americans”). However, there are other ways of quantifying the cost of the keeping the penny in circulation. One way is to look at the embodied energy of a product, which is the energy invested throughout an object’s lifecycle including raw materials acquisition, production and beyond. When the embodied energy of a penny is considered, it is clear that the cost of producing the penny far outweighs its face value.
An object’s lifecycle begins with raw materials acquisition, which, for the penny, is mining. Since 1982, the penny has been made from 97.5% zinc and 2.5% copper: zinc core between two layers of copper (“What’s a Penny Made of?”). The US Mint buys the blank coins that will become pennies from Jarden Zinc Products (“U.S. Penny to Be Kept as Canada Bids Coin Farewell”).
Though statistics on zinc mining are difficult to find, the energy used for zinc production can be inferred by analyzing where and how often energy enters the zinc lifecycle. The zinc for Jarden Zinc Products and comes from Nyrstar Tennessee Mines, which is an operation consisting of six underground zinc mines across four Tennessee counties (“Tennessee Mines Fact Sheet” 1). Statistics on the energy consumption of zinc mining are difficult to find, but Zinc.org gives the following statement on the embodied energy of zinc:
“Among the non-ferrous metals used in building, zinc has the lowest embodied energy. It is the least energy intensive to produce, requiring one fourth the energy of aluminum, and one third that of copper or stainless steel. Zinc is less expensive to extract than many other metals, and requires lower heat and less energy to process.” (“Zinc for Life FAQ’s”)
However, this statistic may be skewed, as the same page defines embodied energy as the total non-renewable energy investment, whereas this report includes renewable and non-renewable energy in the definition. Even without specific numbers, we can analyze points at which energy enters the mining process as a reference.
Zinc mining involves the establishment and maintenance of a large, underground infrastructure. Merrie Long of the Knoxville News Sentinel provides a video tour of Immel mine (one of the Nyrstar Tennessee Mines), for Go Knoxville. In the video, Long travels with miners 2000 feet below ground, where we see the infrastructure that facilitates the mining. Diesel fuel and electricity enter the life cycle by powering transportation vehicles, heavy machinery, and the mining infrastructure before mining even begins (“Life Cycle Assesment” 4). The mining itself begins when holes are machined into tunnel walls where veins of zinc ore are located. The holes are filled with dynamite, and the resulting rubble and ore are brought to the surface. The rubble itself is only 5-15% zinc (“Zinc Production – From Ore to Metal”).
Next, the ore goes through various stages of pulverizing and separating, known as comminution (“Life Cycle Assesment” 4). In the video by Long, this takes place at Young Mill, which is also part of Nyrstar Tennessee Mines. Here, fuel and electricity enter the lifecycle again, this time to pass the ore through the stages of primary crushing, secondary crushing, separating, screening, heavy media separation, and rod/ball milling (“Tennessee Mines Fact Sheet” 1). The result is ore slurry, which is further refined through froth flotation (“Life Cycle Assessment” 4). When the product leaves Young Mill for Nyrstar’s Clarksville location, it has been processed into zinc concentrate, which is 55% zinc (“Zinc Production – From Ore to Metal”).
Like the mining process, the smelting and producing of zinc ingots requires a large infrastructure powered by electricity. Nyrstar’s Clarksville zinc refinery is currently the primary zinc producer in the US. Here, the zinc concentrate goes through five steps to become zinc ingots and alloys (“Clarksville Fact Sheet” 1). First it is heated to 900 degrees Celsius to remove sulfur from the concentrate, a process called roasting. Next come the hydrometallurgical processes. In a process called leaching, sulphuric acid (a by-product of roasting) is used to separate lead and silver from the concentrate. (“Zinc Production – From Ore to Metal”). Zinc dust is added in the purification stage. The electrolysis stage uses electric current to deposit zinc on an aluminum cathode. The zinc that is stripped from the cathodes is what goes into zinc ingots. Each step in the smelting and purification process uses electricity directly or uses electricity and fuel to power the infrastructure that makes production possible (“Life Cycle Assesment” 5).
As stated on Zinc.org, zinc takes a third of the energy it takes to produce copper (though we know Zinc.org does not consider renewable energy in its definition of embodied energy) (“Zinc for Life FAQ’s”). The disparity is caused by mining processes and the quality of copper that is mined. We were unable to locate the mine from which Jarden receives copper for their penny blanks, but my group chose to look at Morenci mine in Arizona as a reference. According to Mining-Technology.com, copper mining at the Morenci mines in Arizona involves three open-pit mines, where a similar infrastructure to the Tennessee mines is located above ground. Electric rotary rigs drill into the walls of the pits to create holes for blasting. Instead of a lift, the rubble is loaded onto trucks. The ore collected here is only an average of .29% copper (“Morenci Copper Mine”).
My group toured the Old Mint in San Francisco. Though we could not find information on modern minting practices, we were able to see the space where minting would have taken place. Most of the pressing of the designs would have taken place in a single room. Though the machines did not take up much space, much force is used to press a design into each and every penny. A photo taken in the Mint Museum in Philadelphia from CoinNews.net shows that it takes 35 tons of force to press a design into each penny.
According to the US Mint’s 2011 Sustainability Report, the US Mint was failing to reduce energy consumption despite an initiative to reduce consumption 30% by 2015. The report lists the US Mint’s total energy consumption in 2011 as 694,462.4 gigajoules, or 192,906,111 watt-hours. This includes consumption of natural gas, diesel, liquefied petroleum, electricity and steam. (“The United States Mint’s 2011 Sustainability Report” 18). Subsequent annual reports describe drops in emissions but mentions of energy consumption in the same depths as the 2011 Sustainability Report do not exist.
Because the penny requires no maintenance and is not recycled, the lifecycle ends at production.
This chart from CoinCollecting.com illustrates the cost to mint a penny from the annual reports from USMint.gov. The last annual report lists the cost of making a penny at 1.83 cents, but it does not take into account the embodied energy of each penny. Though exact numbers are difficult to locate, the infrastructure, transportation and mining processes are all energy intensive, and nonetheless result in a product that is produced at a loss. The information makes it clear that it is time to rethink not only the design of the coin, but and the design industry behind it as well.
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11 December 2014
The U.S. One Cent Coin: Waste & Emissions
Value of the U.S. Penny
Composition of raw materials that make up the one-cent coin, which are primarily zinc and copper, have been altered multiple times throughout history in order to accommodate for socioeconomic factors that have contributed to either significant demand (as per wartime eras) or inflation of costs of copper and zinc minerals. According to the United States Mint, from the first one-cent coin struck in 1787 up until 1837, the composition of the U.S. penny was 100% pure copper, before it was switched to bronze (95% copper, 5% tin and zinc). Copper, zinc, and a small amount of tin became the primary metal composition of the U.S. penny up until 1962, when tin was removed altogether. Copper-plated zinc has become the replacement in recent years for the one-cent coin blanks, which has resulted in a significantly lower percentage of copper in the penny and a higher percentage of zinc (97.5% zinc, 2.5% copper). The degradation of the surrounding areas in which the mineral extraction and smelting facilities are fixated (which can cover entire landscapes) can, more often than not, be traced back to the extraction of these minerals (zinc and copper) from the earth and the waste that is excreted during every step of the process. Rarely do we ever put any critical thought into the nation’s one-cent coin which appears to be abundant in number, yet unwanted all the same by anyone other than large zinc and copper enterprises. According to figures released by the U.S. Mint, 6848.40 million one-cent coins have currently been produced by both the Denver and Philadelphia mint facilities as of November 2014, and cost $1.83 to make per dollar (100 pennies) (Ingraham). Face value of the current U.S. penny does not only inaccurately portray its economic value, but the environmental costs for its industrial purposes as well.
Inside Our Pennies | Copper: From Mineral Extraction to the Penny
For a long time, during the early years of our nation’s history of currency, copper was the main component of the one-cent coin. Copper, which is regarded highly for its alloy-ability, conductivity, and resistance to corrosion, can generally be found in the earth in three basic compounds – native (“pure” copper), oxide (copper-oxygen compound), and sulfide ores (copper-sulfide compound). Native and oxide copper require simple smelting methods for removing waste materials in order to produce a ‘pure’ copper, while sulfide ores (which are the most abundant copper ores found on earth) require a more complex method of roasting (process of exposing materials to high levels of heat) before the actual smelting process to remove sulfur and oxygen components (Morin 1). Copper smelting, as defined by Morin in his book The Legacy of American Copper Smelting, is the art and science of extracting and refining the metal from its ore which follows the general production process as displayed in the table below, with the waste and emissions that are given off during each stage included:
The Mine: Mining the ore.
The Mill: Milling to concentrate the ore and remove large portions of waste. Excretes Tailings
Roasting: Roasting of ores in order to remove iron and sulfur. Sulfur dioxide and heavy metals
Smelting: To transform the ore into a much purer metal. Sulfur dioxide, heavy metals, slag
Refining: Purification of the metal in order to be used for industrial purposes. Sulfur dioxide, heavy metals, slag
So, where do these processes occur? Who conducts them? One notable area, in relation to the copper supply for the U.S. penny, is the Morenci Mine: an open-pit copper mine located in Southeast Arizona, owned by Freeport-McMoRan, that is North America’s leading copper producer (“Arizona Copper”). Mining technology such as blast-hole drills, rotary gigs, and rope shovels are all utilized in order to mine the pit; hundreds of them are powered by internal combustion engines that consume oil and gasoline, every day, in order to generate enough energy to bore, crush, and transport rocks and minerals. These heavy pieces of machinery also release large amounts of hazardous carbon dioxide gas, which is well-known for creating smog over cities, their negative effects to our earth’s ozone layer, and direction contribution towards global warming.
As mentioned in the graph above, concentrations of sulfur dioxide (SO2) emissions are released into the atmosphere throughout a majority of the pyrometallurgical process, due to the burning of mineral ores. A publication by the U.S. Congress, Office of Technology Assessment called Environmental Aspects of Copper Production goes into great detail the impact of sulfur dioxide emissions on air and water quality, and the ways in which they are controlled. According to this document, 0 to 50,000 premature deaths per year in the U.S. and Canada are from SO2 and secondary pollutants from all emission sources (p. 162). For copper smelting, acid plants utilize methods to convert streams of SO2 gas into other materials such as sulfuric acid, elemental sulfur, and liquid sulfur dioxide. Sulfuric acid production, for example, collects hot gases from roasters, furnaces and converters, which are then cooled, cleaned and treated with more sulfuric acid to remove water vapor (p. 163). While these methods may be effective, there comes a large expense economically and energy-wise to convert SO2 emissions. Creating an elemental sulfur by-product, for example, is expensive and requires triple the energy requirement of hydro-carbon fuel (such as coke) of the control system itself (p. 165).
From the milling to the smelting and refining processes, ample quantities of slag and tailings waste by-products are produced (among a variety of others). Slag is the only one of the two that can be directly recycled into materials for other uses such as cement, yet even then may contain potentially toxic elements that are eventually released into the environment and cause pollution of soils, surface waters, and groundwaters (Salisbury). Fine particle waste residue from the extraction process of valuable minerals from mined ores make up 95-99% of the crushed and ground ores, and are called tailings – they can contain leftover processing chemicals, and are particularly difficult to manage due to their high water content (Edraki 411). Historically, waste of tailings have been deposited directly into lakes, rivers and streams, and have resulted in the direct disruption of aquatic life due to the introduction of foreign sediments into the habitats (“How Are Waste Materials Managed?”). Efforts to manage tailing mine waste other than disposal into rivers, lakes and the ocean, include valley or hillside dams, raised embankments or impoundments, dry-stacking of thickened tailings, and backfilling of abandoned mine pits or underground mines (Edraki 411). Tailings dam failures, which account for a majority of mine-related environmental incidents, and tailing sediment run-offs only magnify the geochemical after-effects that poor mining waste disposal have on the environment.
Modern Extraction Alternatives
Some modern methods of copper extraction include a combination of leaching and electro-winning techniques. Leaching and electro-winning are hydrometallurgy extraction processes that utilizes acids and aqueous solutions in order to retrieve copper from the ores, and are considered innovations from the traditional pyrometallurgical extraction processes (Dresher). Due to the use of aqueous solutions for extraction, leaching and electro-winning are considered “greener” alternatives, and are less harmful to the environment because no gas pollutants are released. While this may be the case, it does not mean that these processes do not leave behind waste, especially since leaching and electro-winning both use highly acidic chemicals that are potentially toxic. In fact, leaching waste is usually contained in open ‘ponds’ to be reused, and create a very toxic solution due to the unwanted metal concentrated within it (“Environmental Impact”). Research of recorded leaching acid spills by the Community Water Company show that the spills have the ability of impacting groundwater, which is located several hundred feet below the earth’s surface, and can eventually reach nearby public supply wells (“Environmental Impact”).
Inside Our Pennies | Zinc: From Mineral Extraction to the Penny
While the copper content in the current U.S. penny is only used as a copper plating (2.5%) over the actual primary element within the penny that is zinc (97.5%), the raw material acquisition process and the waste emitted from them are nearly identical. One of the suppliers of zinc material for the current one-cent coin is the Red Dog Mine in Alaska, which is also the U.S.’s largest zinc mine, and represents 79% of total U.S. zinc mine production. This open-pit mine uses a froth flotation technique to separate lead and zinc from ores, using approximately 200 tons of cyanide per year to increase separation efficiency, and leads to a critical problem called acid mine drainage (Coil et al.). Sulfuric acid can form when rock and minerals containing sulfide is expose to the air. Red Dog’s prevention technique for this includes impounding mine tailings with waste rock underwater or on the surface (where acid can still become generated) to create a tailings pond, which is treated before being drained. An argument supporting this technique is that the acid run-off and tailings are maintained onsite to contain the potentially hazardous acid solution; however, the contamination of downstream waters continue to pose a threat if the impoundment is not constantly maintained (Coil et al.). According to the Alaska Department of Natural Resources, if the Red Dog mine continues to operate, they will have produced an estimated 88,000,000 tons of total mine tailings by 2031.
Zinc metal production, as with copper and many major metals, is highly carbon-intensive. Carbon emissions released from the process contribute to the steadily increasing levels of greenhouse gases that endanger our earth’s infrastructure. Site CO2 emissions from zinc mining averaged 0.58 t CO2/t compared to copper’s 2.45 t CO2/t in 2007; mining, shipping, smelting, and refining altogether came out to 2.28 t CO2/t zinc and averaged 3.33 t CO2/t copper (“Carbon Emissions”). These numbers, while are consistent with energy requirements for refined metal production (35.7 GJ/t for copper, 24.5 GJ/t for zinc), merely highlights the amount of energy consumption and carbon emissions released during mining and metallurgical plant operations.
Penny Minting/Production Process: Where do they go?
Once the metals are produced and prepared for industrial purposes, they are transported to various locations in order to establish the framework of the penny. Due to the minimal amount of information available about who the suppliers and manufacturers were for the current U.S. penny, it made the initial research for this part of the lifecycle particularly difficult. The U.S. penny is made from copper-plated zinc blanks (zinc blanks that have been infused with a copper sheet cover, created by using excessive amounts of energy and force to pound them together), and our research revealed that Jarden Zinc was one of the primary suppliers of zinc coinage blanks (which are called planchets) for the pennies created by the U.S. Mint (How Pennies Are Made). Reports on Jarden Zinc processes and waste/emissions for production have either been removed or are unavailable online, and despite many e-mails and phone calls, have not received any reply from them. However, we were able to discover that Jarden Zinc’s mining resources come from the Tennessee Valley Mines (which is comprised of six separate mines: Young, Immel, Coy, Elmwood, Gordonsville and Cumberland) (Jarden Zinc Product Guide). Once the copper-plated zinc blanks are manufactured by companies like Jarden Zinc, they are then sent to the U.S. Mint, where they are heated in giant furnaces to soften the metal, quenched (in a water and chemical solution), cleaned (with chemicals), put through an upsetting mill to raise the rims in preparation for coin pressing, then struck by coin dies to achieve their symbolic penny image design (Unser). A coin die is an engraved metal stamp installed onto the minting machines that is used to imprint the design on each side of the penny; each copper-plated zinc blank is minted with 100 to 150 tonnes pressure (“Designing and Minting”).
Only two U.S. Mint facilities produce all of the minted coins in circulation; one in Philadelphia, and the other in Denver. From these two mints, they are then transported to the 12 Federal Reserve Banks across the nation that distribute the coins via coin terminal operators to depository institutions that order the coins to meet retailers’ and the public’s demand for them (James, Lorelai St. 6). Moving the minted pennies from the Philadelphia and Denver Mints to the Federal Reserve facilities alone releases and consumes gases that leave their own carbon footprints, as air (planes), land (trucks, trains), and sea (ships) transportation methods are used. Distance from the U.S. Philadelphia Mint from the Dallas Federal Reserve Bank, for example, is around roughly 1503.83 miles. Assuming that an ordinary semi-truck with a full load averages 5.5 to 6.5 mpg (232 to 274 mpg), and using numbers provided by the U.S. Energy Information Administration, 22.38 lbs. of CO2 are produced by burning 1 gallon of diesel fuel. This means that the truck transporting the pennies has released approximately 5192.16 to 6,132.12 lbs. of CO2 into the atmosphere. Diesel fuel consumption for transportation in 2013 had emissions of 427 million metric tons of CO2 which, when combined with the numbers for gasoline, totaled to about 1,522 million metric tons of CO2 (EIA). While many are quick to defend diesel-consuming semi-trucks to be one of the “greenest” methods of transportation, there is no denying the fact that the carbon footprint that it leaves behind is a contributing factor to the degradation of our earth’s ozone layer.
Recyclability of the Penny
Once the pennies are distributed, then what? Where do they end up? There are multiple ways in which pennies are used other than being put back into circulation. The melting down of the penny in order to extract the raw materials (such as copper) is illegal in the United States unless handled by the Federal Reserve, so recyclability by means of reverting back to their elemental forms is not particularly a popular resolution. Pennies can also be found in the pockets of coin collectors, though this ultimately is limited to the special edition and ‘collector’s’ version of them. Pennies can also be repurposed for recreational projects, such as art: given their abundance, penny art for large scale projects are not uncommon. Usually, however, the fate of the penny is treated as the lowest coin denomination that it is, despite the effort and costs made to produce it. Pennies end up forgotten on streets, in the bottom of bags and purses, in between seat cushions on the couch, or left in a change jar – forgotten and, ultimately, unwanted.
A Penny’s Worth
Pennies are a hot debate within our society today, boiling down to two straight-forward and seemingly simple resolutions: to keep, or not to keep? On one hand, the penny has been around since the beginning of the history of our nation’s currency and, in a way, is symbolic in that nature. However, given the amount of energy, money and environmental sacrifices invested into the production process – from raw material acquisition up until it reaches the hands of the public – and with the fact that only major copper and zinc suppliers are lobbying in favor of keeping them around, should we not be asking ourselves: “Is it really worth it?” Pennies should be removed from circulation for the good of not only our nation’s economy, but for the surrounding environment in which our economy and the people thrive. So the next time you find a penny in your pocket, or on the street, remember that the true worth of the penny – the energy, time, and environmental costs that it took to be placed in the palm of your hand – far exceeds its face-value.
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