Copper is the second most useful iron used by humans. Most of the world’s copper comes from only a handful of mines.
U.S. copper today is produced primarily by pyrometallurgical smelting methods. This technique uses heat to separate copper from copper sulfide ore concentrates.
In order to be effectively used, mined copper must undergo a series of steps to be properly refined, which are:
- Fire and electrolytic refining
Copper ore coming from mines is less than 1 percent copper. It is crushed, ground, and processed by flotation purification techniques to remove impurities. The resulting concentrate is about 15 percent copper.
Roasting is performed in copper smelters heated in air to 1200oF. During the process, unroasted concentrate is melted with flux in the smelting furnace to produce copper matte, which remains at the bottom of the furnace until tapped. Copper matte contains about 40 percent copper.
The mixture floating on top of the copper matte is then subjected to heated air rich in oxygen, resulting in sulfur dioxide gas being released. The slag is poured off. Finally, the blistered copper is subjected to electrolysis. In the electrolytic process, metallic impurities are precipitated as sludge, which is removed. The resulting copper is 99.96 percent pure.
In 1868, copper was discovered in White Pine County, Nevada; however, without sufficient demand, lack of transportation, and difficulty in extracting, copper was unprofitable to mine. The White Pine Copper Company was organized in 1902, and it solved problems related to metal extraction and transportation.
The McGill Smelter was completed in 1908. The 9-acre area caught fire and burned to the ground in July 1922. According to legend, the product in the crucible splashed onto and ignited the building structure, but the fire was actually caused by a motor overheating.
Fortunately, no one was killed, but it was feared that the loss of the Smelter would turn McGill and the surrounding areas into ghost towns. At the time, Nevada supplied a large portion of the U.S. copper. In desperation, a telegram was sent to D.C. Jackling, Company President, asking what should be done. His reply was simple: “Rebuild it.”
Rebuilding that incorporated the latest improvements and machinery to provide for greater copper recovery occurred four months after the fire. By 1930, the Smelter handled 14,000 tons of copper ore daily.
The history of Nevada is, to a great extent, the history of its mining. Nevada became a state due to the importance of Comstock Silver in the Civil War. Boom towns brought people to Nevada from all over the world. Regional mines currently hire around 10,000 employees, and mining support companies add 1,000 additional jobs to the mining industry cluster.
Before 1982, pennies were made of an alloy high in copper, the majority of which came from copper at the McGill Copper Mill. In 2009, Nevada copper production was reported at 145.7 million pounds.
(1) Mr. Sean Pitts/Director, Department of Cultural Affairs, East Ely Railroad Depot Museum, State of Nevada
Photos courtesy of Department of Cultural Affairs, East Ely Railroad Depot Museum, State of Nevada