Smelting Aluminum on the Moon | Moon To Stay

In 1903, the wright brothers flew the first powered aerial vehicle, the Flyer-1. They originally tried to use a car engine but that turned out to be too heavy so they developed a completely new engine with aluminum. The resulting lightweight 13 hp engine allowed the Flyer-1 to finally make history with orville wright at the controls for a 12 second and 36.5m flight. Just 6 years later, the Junkers J1 was the first airplane with an aluminum body.

In the world of Aerospace, aluminum is perhaps the most used material. It has some great properties that make a lot of sense for building things that need to fly. First and foremost is the weight. Aluminum is lightweight which makes it more efficient for something that you are going to have to accelerate and decelerate and lift into the air. Every kilogram added to a vehicle, removes a kg of potential payload, so making rockets and planes with aluminum is better than steel in that regard. Aluminum is also stable, it doesn’t rust like iron, or explode like sodium metal. It is rigid and strong unlike lithium or gold. All in all, Great properties to have for building things with.

With more than 100 years now of experience building things with aluminum for aerospace, it’s also a material we understand quite a lot about. There are well understood alloys of aluminum that can be referenced easily by engineers and acquired very cheaply.

Aluminum is a global commodity, with massive economies of scale and vast stockpiles. With scale comes accessibility and lower cost compared to something exotic. Aluminum is relatively easy to order, there are many people familiar with how to weld, cut and build with it – making hiring easier. These all play into making aluminum more appealing than many of the alternatives.

As we look towards our future in space it is likely that Aluminum will continue to be a critical ingredient for humans to thrive. But if we want to build truly large facilities and rockets to support large populations of people in space one day then lofting all that material up from the Earth will be costly.

That’s Why we should be interested in mining aluminum on the moon.

Aluminum appears to be quite abundant in minerals on the moons surface. In fact, It is the 3rd most abundant element on the moon behind Oxygen and Silicon, and makes up something between 4-10% of the mass.  Abundance should mean that it is easy to find and access minerals with adequate aluminum content. This is helpful, especially early on with building a permanent moon base because it won’t require a long period of prospecting – like we might expect if we were looking for gold deposits there.

The lunar samples we have collected from the Apollo missions showed quantities of Anorthite. A mineral consisting of aluminum, silicon, calcium and oxygen. For every metric ton of Anorthite processed we would yield approximately 460 kg oxygen, 193 kg aluminum, 201 kg silicon, and 144 kg calcium.  

I tend to think that one of the reasons people talk about mining aluminum on the moon as one of the first things we would want to extract is because it’s such a popular metal to work with on earth – for the reasons I mentioned earlier. However, the moon presents a difficult challenge when it comes to implementing a smelting process. And given the power required to smelt aluminum compared to Iron, there might be a case to be made that we should build lunar infrastructure with iron instead.

Most aluminum we use is smelted using the Hall–Héroult process, where the mineral alumina (aluminum oxide) which is refined usually from mined bauxite, is dissolved in cryolite and then electrolyzed with a carbon anode. This process uses massive amounts of electricity to both heat the solution and run the electrolysis. Also, the anode carbon material is used up and converted to carbon monoxide and carbon dioxide. In effect the oxygen is taken off of the aluminum and bound to carbon instead.

There are a couple of negatives to this process

  1. It requires lots of carbon for the anode, typically this is provided by coke carbon refined from petroleum products.. This is, unfortunately, not available on the moon.
  2. Production of carbon dioxide, is terrible for the environment on earth, and useless to us in space without extra processing to get the oxygen out using something like the sabatier process (like they use on the air recyclers on the space station)
  3. Production of aluminum uses so much electricity that most smelters are strategically located next to very large, low cost power stations. Luckily for the environment these are usually hydro dams. But the amount of electricity required to pull oxygen off of aluminum is extremely high
  4. The hall-heroult process requires alumina, which for the moon would need to produced with another process to convert the anorthite and anorsite minerals we’ve found on the moon.

Luckily, there is some progress being made on scalable carbon-free smelting processes. A promising line of research  is being done as a joint venture between two of the worlds largest aluminum companies. Alcoa and Rio Tinto have started a company called elysis to work on industrial scale carbon-free aluminum smelting. It is being funded by investment from the Canadian Federal government, quebec government and Apple in an effort to further their environmental goals. They are not yet investigating the viability of their elysis process for the moon, but hopefully someday. There is also the FFC Cambridge process which could be promising way to extract elements out of the minerals on the moon with direct reduction of the aluminum, calcium, silicon and oxygen elements from the anorthite mineral.

When we look at the elements it seems that everything we need is there on the moon for us to use. If we had a way to mine various aluminum minerals and extract both the aluminum and oxygen, then we would have material to build with and air to breath. Two critical elements that would greatly reduce the need to ship more supplies to a base on the moon.

What about the power requirements. Once aluminum is bonded with oxygen it requires quite a lot of electricity to reverse the process. As I said, on earth aluminum production can often use the entire output of a massive power station. Also depending on the process used many of these need to maintain high temperatures to keep metals melted – if it cooled down to solidify, things would probably break. We may need steady power supplies – luckily we have perpetual solar at places near the lunar poles.

We can produce oxygen on the moon from the water there with a much easier process. So we don’t need to get our oxygen from aluminum smelting. This frees us to start with small scale experiments to discover the best way to smelt aluminum in space.

Getting beyond hobby scale production of aluminum – enough to do things with – is going to require a robust process and plenty of automation. The last thing we want to do is send people to the moon to shovel dirt all day. We need robots that can go out on their own collect minerals, we need a machine to do the refining that doesn’t require constant vigilance or too much maintenance. People are working on these things, but when might we see some of this tech deployed?

Solving the technical challenges for this will have direct benefits for us on Earth.

  • A carbon-free method for smelting aluminum will help with climate change. Aluminum production is one of the largest single sources of carbon dioxide
  • Automated mining robots will help to reduce costs and improve safety of mining operations here too.
  • Power requirements will demand that we invent solar or reliable nuclear power that can be deployed on the moon

The trouble is that right now there is no market for any aluminum if it were to be produced on the moon.

Before there can be a market for the products we produce on the Moon, we need to get people there. Once people are there, they can be tasked with making larger greenhouses, or more protection for habitats, or larger solar arrays. That has to happen first before someone will create external demand for that aluminum.

The use of Aluminum in Airplanes starting with the wright brothers kicked of a revolution of our knowledge of the metal because it was so critical to making better airplanes. And today, more than 100 years after that fateful first flight, the aerospace industry continues to drive even more advances in our use and production of aluminum.