The Moon is a pretty inhospitable place for humans. It’s all dry and dusty, and there’s no atmosphere for us to breathe. But there is a bunch of oxygen: The lunar regolith – the crumbly top layer of dirt and rubble on the Moon’s surface – is loaded with it. And now scientists have figured out how to get it out.
The process also doesn’t produce waste. On the one hand, you get a bunch of oxygen. On the other, a bunch of metal alloys that it was bound up with. Both of these would be really useful on any future lunar bases or colonies.
Thanks to regolith samples returned from previous lunar missions, we know that oxygen is really quite abundant up there. Between 40 and 45 percent by weight of the regolith is oxygen – by far the most abundant component by weight.
“This oxygen is an extremely valuable resource, but it is chemically bound in the material as oxides in the form of minerals or glass, and is therefore unavailable for immediate use,” said chemist Beth Lomax from the University of Glasgow in Scotland.
Those samples are too valuable to experiment on directly, but having them means we can precisely recreate their consistency using terrestrial materials. This ‘fake’ lunar dirt is called lunar regolith simulant, and Lomax and her team used it for their research.
There have been previous attempts to extract the oxygen from lunar regolith, such as the chemical reduction of iron oxides using hydrogen to produce water, and then electrolysis to separate the hydrogen from the oxygen in the water; or a similar process with methane instead of hydrogen.
But these techniques have either been low-yield, overly complicated, or too hot, requiring such extreme temperatures that the regolith actually melts.
Lomax and colleagues have skipped the chemical reduction step and gone straight to electrolysis of the powdered regolith.
“The processing was performed using a method called molten salt electrolysis. This is the first example of direct powder-to-powder processing of solid lunar regolith simulant that can extract virtually all the oxygen,” Lomax explained.
“Alternative methods of lunar oxygen extraction achieve significantly lower yields, or require the regolith to be melted with extreme temperatures of more than 1,600 degrees Celsius (2,900 F).”
First, the regolith is placed in a mesh-lined basket. Calcium chloride – the electrolyte – is added, and the mix is heated to around 950 degrees Celsius, a temperature that doesn’t melt the material. Then, an electrical current is applied. This extracts the oxygen, and migrates the salt to an anode, where it can be easily removed.
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