Removing the copper (and other metals like zinc, lead and molybdenum) typically found in sulphide ores involves a process of burning the minerals to remove the sulphur, which produces sulphur dioxide- a dangerous chemical that is converted to sulphuric acid.
Now a team of MIT researchers in the United States has shown that they can separate pure copper and other trace elements from sulphur-based minerals using molten electrolysis. Under the process, an electric current is passed through a molten substance, which produces a chemical reaction that separates the materials without producing toxic byproducts such as sulphur dioxide.
By forming liquid copper metal and sulphur gas from an electrolyte composed of barium sulphide, lanthanum sulphide and copper sulfide, they were able to get yields greater than 99.9 percent pure copper – equivalent to the best current copper production methods, according to MIT News.
“It is a one-step process, directly just decompose the sulfide to copper and sulfur. Other previous methods are multiple steps,” post-doctoral researcher Sulata Sahu explained. “By adopting this process, we are aiming to reduce the cost.”
The work builds on a 2016 paper published in the Journal of The Electrochemical Society which offered proof of electrolytic extraction of copper.
“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. There is a tiny fraction that is ionic, which is good enough to make copper,” said Antoine Allanore, assistant professor of metallurgy at MIT.
The experiments were conducted at 1,227 degrees Celsius, which is about 150 degrees above copper’s melting point and the temperature commonly used for industrial copper extraction.