Rare earths: where to find them?

Using a bacteria-inspired hack to optimise rare earth mining
05 October 2021

Interview with 

Joseph Cotruvo, Penn State University




To another technologically important element - or rather, group of elements - the rare earths. These are a group of 17 chemical elements with special properties that make them well suited to all sorts of tech applications, from making the bright colours in your phone screen to fuel cell batteries and electric vehicle motors, which means we need a lot of them. But currently, the supplies are dominated by certain countries, China in particular, that have also used their monopoly over this market to exert political and diplomatic pressure on other nations. So is there a way around this? Chris Smith spoke with Joseph Cotruvo, from Penn State University. He’s working on techniques that make it easier to get hold of the rare earths we need...

Joseph - The rare earths are really not particularly rare. There's more of the most abundant rare earth, an element called cerium, then there is copper in the Earth's crust, but the problem is that they're not distributed very evenly. And so the rare earths are rare because they're usually present in rocks in very low amounts, they're mixed with other rare earths and they're mixed in with many more abundant metals like iron, calcium, and others. And so as a result, there are very few deposits that are economical to mine those metals

Chris - And hence we have the sort of geopolitical issue, and supply issues, just because of gaining access to where they're actually worth exploiting?

Joseph - Exactly. Right.

Chris - What are the possible solutions then?

Joseph - Well, so the solution that we have been working on uses biology, or biochemistry I should say. Really about a decade ago it was discovered that there are actually bacteria that need some of the rare earths, just like we need metals like iron or calcium or zinc, as vitamins, essentially. And so I thought that if we could understand how these bacteria have basically solved the problem of mining rare earths, the same problem that we want to solve, we may be able to do this more efficiently. And so my lab discovered the first molecule that these bacteria make that binds rare earths very tightly and very specifically. It's a protein molecule, and you can think of it as a person with arms that are flailing about. When the hands on those arms grab hold of a rare earth, the body curls up into a ball and they can hold onto the elements very tightly. But if the arms grab a metal that is not a rare earth, it tries to curl up, but it can't. And therefore it has to release those metals. And so essentially what we would like to do, if we can take the protein that's curled up into this ball, and when we want to recover the rare earths from the protein, we can tickle it so to speak to get it to release the metals, and then we can go on and use those metals for technologies.

Chris - Presumably the tickle is a chemical one -  you prise the fingers of the arms off of the metal chemically to make it surrender what it's grabbed. What though, I'm intrigued to know, are the bacteria. What are they and why have they got this extraordinary function?

Joseph - Yeah, most of the bacteria that use rare earths are a class of bacteria called methylotrophs. These bacteria are actually all over the place in the environment -  in soil, in water, they grow on plants, and they're present in more extreme environments too. And they're really special microbes because they can use very simple molecules like methane and methanol, molecules that we can not use as food. And so what the rare earths are doing in these bacteria is they helping to catalyse a very important chemical reaction, basically how those bacteria eat, the methanol that they use as food.

Chris - And would your plan then be, having discovered how the bacteria are able to grab and sequester these rare earths from very dilute, what will be very dilute sources in the environment, you could borrow from that biology and basically copy it so you'd have a very fine sieve specific for rare earths?

Joseph - Exactly. Yeah, that's exactly it. You know, we could use the bacteria on their own potentially, but biology is a lot slower than chemistry is. The protein on its own, if we can make it and we can make it on its own, it works very, very quickly. So we're using the molecules on their own.

Chris - And in practical terms, how would one deploy this? Would you go to, say, a mine site where someone's already moved - I would say heaven and earth but a lot of earth - and you could take the tailings and basically, you know, there's going to be tiny amounts of rare earth in there and they're not worth processing the traditional way. But you could put that through your very fine sieve, and therefore you would enrich for the rare earth from mess we've already made without having to make a new mess?

Joseph - Exactly. Yeah. There are actually many waste sources, such as the ones that you mentioned, where we have huge quantities of material, but very small amounts of rare earths. And so the mine tailings that you mentioned, coal fly ash, the very acidic water that spills out of mines, also electronic waste. All of these are sources where we have a very large amount of material that can be processed, but the current technologies just don't work. And that's where we can take advantage of the millennia and millennia of evolution, where the bacteria have devised ways of getting out these small quantities of rare earths.

Chris - It sounds incredibly elegant, and congratulations to you for this achievement, but if one tots up how much there is in the way of rare earths in these other sorts of sources that we've just been discussing, is there enough potentially recoverable in there to keep the likes of the makers of iPhones and Android phones and the magnets in electric vehicle motors happy?

Joseph - At the moment I think this isn't the full solution to the problem. Using sources where you're starting with very high concentrations of rare earth will be the best for the next few years. But the demand for rare earth keeps increasing and we have more and more of these wastes. And I think it's important to incentivise sustainability. The mining process of rare earths is one of the most environmentally damaging industrial processes on earth. And so if we recognise some of the hidden environmental costs associated with those methods, then I think, once scaled up, biotech methods like ours could really make a dent in the rare earth problem that exists.


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