DOE awards MIT researchers $1.9M to advance electrolytic production of copper; direct production of copper wire
The US Department of Energy (DOE) has awarded MIT associate professor of metallurgy Antoine Allanore a $1.9-million grant to run larger scale tests of a new one-step, molten electrolysis process (earlier post) to produce copper from sulfur-based minerals—the main source of copper.
One of Allanore’s primary goals is to make high-purity copper that can go directly into production of copper wire, which is in increasing demand for applications from renewable energy to electric vehicles. Production of electric and hybrid cars and buses is expected to rise from 3.1 million vehicles in 2017 to 27.2 million by 2027, with an accompanying nine-fold increase in demand for copper from 204,000 metric tons to 1.9 million metric tons (2.09 million US tons) over the same period, according to a March 2017 IDTechEx report commissioned by the International Copper Association (ICA).
In June 2017, researchers in Allanore’s lab reported a promising method of forming liquid copper metal and sulfur gas in an electrolysis cell from an electrolyte composed of barium sulfide, lanthanum sulfide, and copper sulfide, which yields greater than 99.9% pure copper. This purity is equivalent to the best current copper production methods.
(An electrolysis cell is a closed circuit, similar to a battery, but instead of producing electrical energy, it consumes electrical energy to break apart compounds into their elements—e.g., splitting water into hydrogen and oxygen. Such electrolytic processes are the primary method of aluminum production and are used as the final step to remove impurities in copper production. Unlike aluminum, however, there are no direct electrolytic decomposition processes for copper-containing sulfide minerals to produce liquid copper.)
The MIT molten sulfide electrolysis process eliminates sulfur dioxide, a noxious byproduct of traditional copper extraction methods, instead producing pure elemental sulfur.
Allanore suggests that the technology could provide copper wires with less energy consumption and higher productivity; it may be possible to cut the energy needed for making copper by 20%.
Currently, it takes multiple steps to separate out copper, first crushing sulfide minerals, and then floating out the copper-bearing parts. This copper-rich material—copper concentrate—is next partially refined in a smelter, and further purified with electrolytic refining.
Professor Allanore’s approach would work on the copper concentrate and has the potential to produce copper rod in a single operation while separating unwanted impurities and recovering valuable byproducts that are also in the concentrate. Professor Allanore’s approach is a big step; it allows a completely new approach to refining copper.—Hal Stillman, director of technology development and transfer for the International Copper Association
The three-year, $1.89 million DOE award will allow Allanore’s group to make a larger reactor, producing about 10 times as much liquid copper per hour, and to run the reactor for a longer time, enough to identify what happens to the other metals accompanying copper, which are also commercially important.
Allanore’s group effort began this year, and he hopes it will provide the data needed to move on to a pilot plant within three years.
Key technical challenges to overcome are proving the durability of the process over a longer time period and verifying the purity of the metals that are made in the process. Some of the byproducts of copper production, selenium, for example, are valuable in their own right.
The revolution that we are proposing is that only one reactor would do everything. It would make the liquid copper product and allow us to recover elemental sulfur, and allows us to recover selenium. We are using electricity, and electrons can be very selective, so we are using electrons in a manner that enables the most efficient separation of the products of the chemical process.—Professor Allanore
Conventional pyrometallurgy produces copper by burning the ore in air, requires four steps and produces noxious compounds such as sulfur dioxide that require secondary processing into sulfuric acid. The resulting initial batch of copper also requires further processing, as it leaves behind copper metal with too much sulfur and too much oxygen for downstream direct wire production, Allanore said.
Allanore lab’s new molten sulfide electrolysis method better handles trace metals and other elements impurities that come with the copper, allowing for separation of multiple elements at high purity from the same production process.
The International Copper Association conducted a Life Cycle Assessment that identified several areas where the copper industry can improve its environmental footprint. The study indicates the industry needs to continue reducing on-site sulfur dioxide emissions and to get its electricity from sources that are more environmentally friendly. Allanore’s project is relevant to both these issues.
If developed and deployed, it has the potential to decrease energy demand, operate entirely on renewable energy, and reduce sulfur dioxide emissions. In addition, it can separate unwanted impurities and recover valuable by-products from the concentrate. Right now, the technical evidence that is creating excitement is a small-scale proof-of-principle demonstration. It’s great that EERE has provided the needed initial funding to explore the potential. If the process works at larger scale, it could be the type of revolutionary approach that the industry is seeking.—s Hal Stillman
Allanore’s award is one of 24 early-stage, innovative technology projects receiving up to $35 million in support announced earlier this year by the US Office of Energy Efficiency and Renewable Energy Advanced Manufacturing Office.
Sulata K. Sahu, Brian Chmielowiec, Antoine Allanore (2017) “Electrolytic Extraction of Copper, Molybdenum and Rhenium from Molten Sulfide Electrolyte,” Electrochimica Acta, Volume 243, Pages 382-389 doi: 10.1016/j.electacta.2017.04.071