IRA FLATOW: This is Science Friday. I’m Ira Flatow. Decarbonization is a net positive for the world, right? Reduce fossil fuel production, reduce CO2 emissions. But there’s an unanticipated side effect. We may be facing a global sulfuric acid shortage– you know, the corrosive stuff that’s in your car battery.

Turns out that 80% of the world’s sulfuric acid is the byproduct of fossil fuel production. Cut back on coal, oil, and natural gas production, and we’re lowering our sulfur supply. Sulfuric acid is critical to making green tech, like solar panels and batteries, and in fertilizer production. Joining me now to explain more about this potential problem is Mark Maslin, professor of earth system science at University College London in London, England. Welcome to Science Friday.

MARK MASLIN: It’s a pleasure to be on.

IRA FLATOW: Nice to have you. Let’s start off by talking about why sulfur is so important to the global economy. What’s it used for?

MARK MASLIN: So sulfur is used to actually dissolve stuff. And what’s really important is it dissolves rock. So for fertilizer production, it dissolves the phosphate rocks and gets the phosphate out, because we know when we actually want to sort of fertilize the land for agriculture, we need both nitrogen and we also need phosphate. And so it’s a really, really quick way of dissolving the rocks and getting that out.

But it also dissolves rock to get at those essential metals. So we’re thinking of lithium. We’re looking at, say, nickel and things like that, which are essential for making lightweight batteries for our electric cars but also for solar panels. And to give you an example, these metals are very rare. So even when they occur in a rich seam, they’re only about 1% of the rock. And so what happens is you use this sulfuric acid, dissolve the 99% away to leave these valuable metals behind.

IRA FLATOW: And before reading your research, you know, I didn’t really understand just how many things sulfur was used for. What got you so interested in this?

MARK MASLIN: I’m always looking at these systems, how the global economy works and how connected everything is. So for example, the invasion of Ukraine stops grain being exported from Ukraine to the rest of the world, which then makes food prices go up in Africa. So we live in a very connected world.

And when we’re looking at decarbonization, we were looking at how this would affect lots of different minerals and metals. And we suddenly discovered that sulfur had been forgotten about. And the reason why it’s been forgotten about is because it is the fifth most common element on planet Earth. And so there’s a huge amount of it, except it’s all locked in rocks, whereas now what we do is we get nice sulfur in its actual yellow, elemental form by getting it out of fossil fuels.

And we have to do that because the legislation around the world says, fossil fuel companies, clean up your gas and oil and coal because we don’t want the sulfur in the actual fossil fuels because when it gets burnt, it produces sulfur dioxide, which creates acid rain. That’s bad. So basically, please get rid of it.

IRA FLATOW: So do they get rid of it? I mean, are we able to mine sulfur and those ores safely and environmentally safe?

MARK MASLIN: So the big problem is, and why we were so keen to get this paper out is, we want to avoid mining sulfur because the way you actually mine sulfur is you pump really hot, supercritical steam– so basically, incredibly hot water– through rocks, which then dissolves the actual sulfur out of these sedimentary rocks. And what you do is you get this sulfuric acid out at the other end. And that sulfuric acid you then collect and then pass around the world.

So that causes two problems. One, actually, as you’re dissolving the sulfur, you’re also dissolving other nasties like mercury and of course arsenic, which can get into the water of the surrounding area. So that’s really bad. Second thing is you’re then having to transport sulfuric acid around the world, which is actually dangerous and difficult, whereas transporting the yellow sulfur solid and then making sulfuric acid on site where you need it is much safer and much easier.

IRA FLATOW: So is it possible to do that, to transport it more solidly, the yellow stuff, around the world?

MARK MASLIN: No, because the only way of actually getting solid sulfur is either from fossil fuels, or you can actually mine it from volcanoes. So in Indonesia, there are lots of people that mine it on the sides of volcanoes and literally chip away at the yellow rock and bring it down. But that’s very small scale. I mean, we’re needing millions and millions of tons of sulfur. So in our paper, what we’re suggesting is, well, how about reducing the need for sulfuric acid, which then reduces the need to get sulfur and hopefully will stop the expansion of mining in the next couple of years.

IRA FLATOW: I get it. So how do you, then, reduce the need for sulfuric acid?

MARK MASLIN: Well, the first thing is, if you think about the fertilizers, phosphate. Well, why create new phosphate when we could recycle it? So there’s a lot of phosphate that is in our sewage. So there are really interesting systems where we could actually recycle that sewage and get the phosphate out and have a bit of a circular economy whereby we make fertilizers, we put it on the land, it goes into our sewage, we then reclaim it and put it back onto the land. So we can start to think of a much more circular economy when it comes to that.

When it comes to metals, again, why can’t we recycle things? We are advocates of making sure that all our products, whether it’s our computers, our phones, whether it’s our electric battery in our car, they should be designed from day one to be recyclable. And therefore, all that lithium that we need, all that nickel, and all of those other metals, actually, we can recycle a lot of them because we can get back all the stuff we already mined, reducing the damaging mining but also meaning that we don’t need so much sulfuric acid.

IRA FLATOW: And what about all these new batteries that I’m hearing about that can use sulfur instead of some of these rare-earth elements in them?

MARK MASLIN: Well, again, this is sort of a balancing act, which is, does the sulfur in the batteries mean that you need less lithium, which means you need less sulfuric acid? Because if you think about it, for mining something like, say, cobalt, you are using about 250 times the amount of sulfuric acid as the nickel you get out. So if you can replace, say, 10 grams of metal with 10 grams of sulfur in your actual battery, then of course you’re going to win in that balancing act.

But what we do need to do is think about new batteries. And this is where the new technology comes in. Can we actually build batteries which are using less rare metals, that are easier to recycle, which actually have a much higher storage and also a longer life? And the technology is accelerating so quickly.

IRA FLATOW: Well, if we don’t find a way, and if we don’t take your advice and recycle a lot of this stuff, of the waste, are we going to have a global sulfur shortage?

MARK MASLIN: There will be a shortage in the future if we don’t actually deal with it now. And what will happen is different industries will be able to pay the higher price. So therefore, if you think about it, the metals industry– a ton of lithium is so much more expensive and profitable than a ton of fertilizer.

So we have the idea that perhaps green tech would outcompete the fertilizer industry. And that means that fertilizers would become more expensive, food production would become more expensive, and therefore, the food that we buy on the shelves would obviously be more expensive. So what we’re trying to do is provide a warning a decade ahead saying, look, we can see this crisis ahead. Why not actually do something about it?

IRA FLATOW: Do you think this will happen? Are you optimistic about this?

MARK MASLIN: Well, I think that we are starting to think in very different ways. I think we are starting to think systematically about the implications for decarbonizing the world, how we actually produce enough renewable electricity, how do we actually transport it, how do we store it in a green way. And again, I think because people are now thinking more holistically and in a more joined-up way, we can put these resource crises into the mix and work out how we can actually mitigate against those.

IRA FLATOW: Thank you very much, Dr. Maslin, for taking time to be with us today.

MARK MASLIN: Pleasure.

IRA FLATOW: Mark Maslin, professor of earth system science at University College London, of course, in London, England.