This happens when extra electrons are introduced to the system by the applied voltage. The desired reaction in an electrolysis cell is to form elemental atoms, by adding electrons to metals such as copper, and taking away electrons from sulfur. In their molten state, copper ions are missing one electron, giving them a positive charge, while sulfur ions are carrying two extra electrons, giving them a negative charge. These sulfide minerals are compounds where the metal and the sulfur elements share electrons. “The new paper shows that we can go further than that and almost make it fully ionic, that is reduce the share of electronic conductivity and therefore increase the efficiency to make metal,” Allanore says. There is a tiny fraction that is ionic, which is good enough to make copper,” Allanore explains. “This paper was the first one to show that you can use a mixture where presumably electronic conductivity dominates conduction, but there is not actually 100 percent. Sokhanvaran is now a research scientist at Natural Resources Canada-Canmet Mining Lee is a senior researcher at Korea Atomic Energy Research Institute and Lambotte is now a senior research engineer at Boston Electrometallurgical Corp. They showed that addition of barium sulfide to a copper sulfide melt suppressed copper sulfide’s electrical conductivity enough to extract a small amount of pure copper from the high-temperature electrochemical cell operating at 1,105 degrees Celsius (2,021 Fahrenheit). The new work builds on a 2016 Journal of The Electrochemical Society paper offering proof of electrolytic extraction of copper authored by Samira Sokhanvaran, Sang-Kwon Lee, Guillaume Lambotte, and Allanore. The researchers also used electrolysis to produce rhenium and molybdenum, which are often found in copper sulfides at very small levels. Most current copper extraction processes burn sulfide minerals in air, which produces sulfur dioxide, a harmful air pollutant that has to be captured and reprocessed, but the new method produces elemental sulfur, which can be safely reused, for example, in fertilizers. “By adopting this process, we are aiming to reduce the cost.”Ĭopper is in increasing demand for use in electric vehicles, solar energy, consumer electronics and other energy efficiency targets. Other previous methods are multiple steps,” Sahu explains. ![]() “It is a one-step process, directly just decompose the sulfide to copper and sulfur. Their results are published in an Electrochimica Acta paper with senior author Antoine Allanore, assistant professor of metallurgy. This purity is equivalent to the best current copper production methods. The MIT researchers found a promising method of forming liquid copper metal and sulfur gas in their cell from an electrolyte composed of barium sulfide, lanthanum sulfide, and copper sulfide, which yields greater than 99.9 percent pure copper. Contrary to aluminum, however, there are no direct electrolytic decomposition processes for copper-containing sulfide minerals to produce liquid copper. Such electrolytic processes are the primary method of aluminum production and are used as the final step to remove impurities in copper production. ![]() They also quantified the amount of energy needed to run the extraction process.Īn electrolysis cell is a closed circuit, like a battery, but instead of producing electrical energy, it consumes electrical energy to break apart compounds into their elements, for example, splitting water into hydrogen and oxygen. Chmielowiec ’12 decomposed sulfur-rich minerals into pure sulfur and extracted three different metals at very high purity: copper, molybdenum, and rhenium. ![]() This one-step, environmentally friendly process simplifies metal production and eliminates the toxic byproducts such as sulfur dioxide. MIT researchers have identified the proper temperature and chemical mixture to selectively separate pure copper and other metallic trace elements from sulfur-based minerals using molten electrolysis.
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