ESA Molten Salt Electrolysis Plant to Study Oxygen Extraction from Regolith
The ESA Molten Salt Electrolysis prototype plant is able to produce oxygen and metal alloys from lunar regolith using nothing but salt and energy. Beth Lomax and Alexandre Meurisse are two ESA research fellows working on this sytem. Credit: ESA-A. Conigili.
A prototype plant for studying the extraction of oxygen from lunar regolith started operations recently in the Netherlands. Located at the Materials and Electrical Components Laboratory of the European Space Research and Technology Centre (ESTEC), this ESA based project is an enabling technology for a sustainable presence on the Moon. Being able to collect oxygen from the bountiful lunar regolith will provide a robust supply of rocket oxidizer, breathable air, and feedstock for industrial processes.
The oxygen extraction method uses a molten salt electrolysis process to remove oxygen from regolith. While molten oxide electrolysis has been utilized for industrial metal processing for over 100 years, using molten salt electrolysis for generating oxygen from lunar regolith is a novel purpose that has yet to be deployed.
Lunar regolith contains up to 45% oxygen by weight, however, it is chemically bound to other elements. Molten salt electrolysis is able to separate the bound oxygen by using electrical energy to break the chemical bond. Molten calcium chloride (950C) acts as a conducting liquid (electrolyte), through which an electric charge passes between an anode and cathode. By submerging the lunar regolith into the molten salt, oxygen is released and attracted to the anode where it can be collected.
While oxygen is produced through this process, metal alloys are also generated from the regolith. Traditional terrestrial electrolysis processes focus on this aspect, where the oxygen and other gasses are waste by-products. In lunar environments, both products are usable.
Even though the basic process has heritage, using molten salt electrolysis on lunar regolith will still require extensive testing. Regolith from different regions likely requires unique process parameters, along with producing different amounts of by-products. Additionally, the power requirements, feedstocks, and structure need to be evaluated for lunar deployment; a non-trivial task.
NASA also has done work with electrolyzing, albeit bypassing a secondary electrolyte like salt, and using the regolith itself in a process they call lunar regolith electrolysis. Not only does this prevent the need for bringing feedstocks from Earth (ie salt), but it creates molten regolith that can be immediately utilized in a follow-on process.
ESA has stated that the ultimate aim for this test plant is to get a demonstration mission ready to fly in the mid-2020s. Developing heavy industrial processes like this systems is required for a sustainable human presence in space, where local raw materials can be high grade resources.
Learn more about ESA’s molten salt electrolysis prototype plant here.
