Kathryn Goodenough on Sources of Lithium for a Post-Carbon Society

Transcript

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Oliver Strimpel

This is Geology Bites with Oliver Strimpel. The lithium ion battery was invented about 40 years ago and is now commonplace in a range of products, from smartphones to electric cars. But if we are to meet the carbon emission goals that governments are setting, electrification, and with it the need for electricity storage, will increase dramatically. Although many new electricity storage methods are being developed, none are as mature as the lithium ion battery, which will therefore need to be a major part of a carbon-free infrastructure. Catherine Goodenough is principal geologist at the British Geological Survey. She studies the geology of critical raw materials and particularly of lithium. She's the principal investigator for the Lithium for Future Technology, an international consortium that investigates all type of lithium deposits and how they can be extracted sustainably. Catherine Goodenough, welcome to Geology Bites.

Kathryn Goodenough

Thanks very much, Oliver. Thank you for having me.

Oliver Strimpel

Let's start with some basics. What exactly is lithium?

Kathryn Goodenough

Lithium is a metal. In fact, it's the lightest of all metals. It has an atomic number of just three.

Oliver Strimpel

What properties make it so useful for making high-capacity batteries?

Kathryn Goodenough

Well, lithium, is unusual because it's very reactive. Many of us may have seen lithium in our school chemistry labs and seeing what happens to it when it comes into contact with water, for example. It releases its electrons very easily, and that means that it has excellent electrical conductivity and low resistivity. So it's very useful for use in batteries. Indeed, there's nothing else quite like it.

Oliver Strimpel

So how does lithium occur naturally in the earth?

Kathryn Goodenough

Well, because it's so reactive, it doesn't occur as just elemental lithium. In rocks it forms a whole range of different minerals. So those minerals are compounds. They might contain a lot of silica, for example, or a lot of phosphate, and there's a very wide-ranging family of those naturally occurring lithium minerals with unusual names like spodumene, petalite, amblygonite, and Lepidolite. But even in rocks that are less rich in lithium, you will find small amounts of lithium where it substitutes for other elements such as magnesium in more common minerals. And then in water, lithium ions are very soluble, so lithium can also occur in brines, and indeed in the sea water, there's quite a substantial amount of lithium.

Oliver Strimpel

So in the sea water, is it also in the form of chemical compounds, or is it in a pure ionic state?

Kathryn Goodenough

Yes, it occurs in an ionic state, and you can also get formation of lithium salts like lithium chloride.

Oliver Strimpel

If we're mining lithium in the form of one of these exotic-sounding minerals that you mentioned, we still have to actually extract the lithium itself from the mineral.

Kathryn Goodenough

That's right, this is a large part of mining. When you go to mine lithium, what you actually do is dig up a rock which contains lithium minerals and a whole range of other minerals. Then you have to separate the lithium minerals from the other minerals and create a lithium mineral concentrate. But even that concentrate may only contain a few percent of lithium. Then we've actually got to break open that mineral concentrate, usually using significant amounts of chemicals, and actually remove the lithium from the mineral. And then we’ll produce a chemical such as a pure lithium carbonate or lithium hydroxide, which can then be used in the battery supply chain. So mining is really only the very first step. There's usually a lot of mineral processing to be done afterwards. If you're mining lithium from a brine, that mineral processing is perhaps a bit easier, but there is still an element of mineral processing that simply can't be avoided.

Oliver Strimpel

Does it take a lot of energy to prise the lithium out of the minerals?

Kathryn Goodenough

It does indeed take either a lot of energy or some very strong chemicals, or both. And research is ongoing to try and develop better ways of processing these minerals.

Oliver Strimpel

I want to ask you about the geological settings in which we find lithium, and you've already mentioned the sea. What about the lithological rock-based settings?

Kathryn Goodenough

The main source of lithium, if you like, from hard rocks, is in granitic pegmatites. Pegmatites are very coarse-grained igneous rocks. They're typically granitic in composition, and they can be found all over the world, most commonly in areas where you've had crustal thickening due to mountain building. Pegmatites can just be quartz and feldspar and not a lot else, but a small subset of pegmatites are lithium enriched, and that's the major source of hard- rock lithium. We do also find lithium in sedimentary sources, so what would have been ancient basins that might have had lithium-enriched brines circulating in them. And in those areas, we can get lithium in lithium-enriched clays or in borate minerals.

Oliver Strimpel

And then also brine.

Kathryn Goodenough

Exactly! Brines are a very important source of lithium. And there's two main types of brines. The one that's currently used for extraction of lithium is brines in the salt lakes, chiefly in South America, where you have closed basins in which brines, rich in lithium, concentrate. And then solar evaporation in an area that's particularly dry leads to the concentration of the lithium and then you can extract from these what are really salty waters. You can extract the lithium. The other opportunity is where you have what's called geothermal or perhaps oil field brines, where you have brines circulating in the rocks, and those may also be enriched in lithium in certain settings. For example, here in the UK we have mines in Cornwall that are known to be enriched in lithium circulating in what were quite lithium-enriched granites. And those are also a potential source of lithium. But those geothermal brines, it's harder to get the lithium out of them, because of course you can't use solar evaporation as a technique. So there's been a lot of research in recent years to develop what's known as direct lithium extraction, where you can remove the lithium from those brines without having to concentrate it by evaporation first.

Oliver Strimpel

So do the brines get their lithium by leaching out rocks, either the pegmatites or the sedimentary rocks?

Kathryn Goodenough

So that's a really good question and one that I think we don't fully know the answer to. But what seems most likely is that the brines get their lithium, and this is the case whether we're talking about the salars, or whether we're talking about geothermal brines, they get their lithium by leaching lithium out of very large volumes of not especially lithium-enriched rocks. So for example, in South America, in the salars, the watersheds surrounding them are typically volcanic rocks because much of the Andes is a chain of volcanoes formed above a subduction zone. And these volcanic rocks will contain some lithium, but it's not enriched enough to be economic in the rocks. But if you have groundwater circulating and surface water circulating and leaching all the lithium that is in those rocks and then collecting it in a closed basin, that can be enough to generate enrichment of lithium in the brines, essentially because the lithium ions are so soluble in the water that they would far rather be in the water than in the rock. And so they will go into the water fairly quickly.

Oliver Strimpel

OK, let's talk a bit more about the geological processes that concentrate the lithium in the hard rock cases. First of all, the pegmatitic granitic rock.

Kathryn Goodenough

The way that you get lithium into a granitic magma is by melting sedimentary rocks that were themselves enriched in lithium. Exactly what type of sedimentary rocks those are we're still not, I have to say, completely clear. And then once you've melted those sedimentary rocks, there’s a big question around how lithium pegmatites are formed, and there's two possible answers. One is you have a large volume of magma that forms a granite body. And that granite starts to crystallize. You get fractional crystallization, so your magma evolves and the lithium remains in that magma, while everything else is crystallizing until you have a very, very lithium-enriched kind of residual magma, and that forms the pegmatites. That's one possibility. The other possibility is that actually as soon as you get melting of lithium-enriched sedimentary, these relatively small amounts of melt can gather together in the crust and form the relatively small bodies that are pegmatites. And when I say relatively small, they're usually tens, perhaps hundreds, of meters thick at most, and they might extend for hundreds of metres to a kilometre or so. That's quite small by geological standards. So we don't really understand exactly what the process is. We know that there must be a lithium-enriched source, probably a sedimentary rock that melts because the crust is being placed under compression and being heated in a mountain belt. And then that must form a magma that has lithium in it. And then there are a couple of different ways in which that magma could potentially evolve to produce lithium-enriched pegmatites. So I think the real answer is there's quite a lot we don't know.

Oliver Strimpel

So it seems like some of this ignorance, if you like, extends back to the sedimentary rocks themselves, which is one of the explanations for the source of the lithium in your pegmatitic granite. So do we know how sedimentary rocks get enriched in their lithium content?

Kathryn Goodenough

Again, there is some uncertainty, there's no doubt about that. We can see what's going on at the moment, of course. The present is the key to the past, and we can see the current salars in the Andes, and we can imagine that if they weren't having their lithium extracted, then those would sit there as salt lakes, and they would eventually form solid salt layers in the geological record. And those solid salt layers would be enriched in lithium,of course. That type of layer can be recognized in some places in the geological record, and perhaps we can see that in these cases there is enrichment in lithium. But, of course, the salt lakes are relatively unusual because of the solar evaporation you need to form them. What's much more likely is that in most cases we've got lithium being washed into more ordinary lakes, where it's being deposited in association with clay minerals. And that gives you the sedimentary rocks that we see. For example, in Nevada, Tesla has talked about potentially getting involved in mining. So we understand how you might form those lithium-enriched clays. But then, of course, what happens to those when they get compressed and heated and eventually melted in a mountain belt? We don't actually know. At the moment what a lithium-enriched clay would look like once it's become metamorphosed and partially melted. The other thing that we're still trying to understand is that some of the most important sedimentary deposits of lithium, like particularly the Jadar deposit in Serbia. These may be original sedimentary rocks that may have had some lithium enrichment, but that then had hydrothermal brines circulating through them and enriching them further in lithium.  For example, in Nevada, the lithium-enriched clays are actually in a volcanic setting, and so we would have had volcanic waters,If you like, that might have had lithium in them circulating amongst those clays.

Oliver Strimpel

Do the various minerals in which the lithium manifests itself give us any clues as to how the lithium got there?

Kathryn Goodenough

They give us some clues, and in particular there's been a lot of really good experimental work done to show exactly which of the lithium minerals you get depends on the pressure and temperature. So, for example, there's two major minerals, spodumene and petalite, that you find in pegmatites. And of those, petalite is formed at higher temperatures than spodumeneis. So you can estimate something about the temperatures they formed at and the depths that they formed at from the minerals that you can see. But one of the things that is really interesting about lithium deposits is this idea of hydrothermal fluids circulating that contain lithium. And we see that consistently the brines are, of course, hydrothermal fluids themselves, and in sedimentary deposits and in pegmatites we see evidence of these hydrothermal fluids circulating and altering the original minerals. And as a result, the original processes by which either the sedimentary deposit or the pegmatite formed have been obliterated by later hydrothermal alteration.

Oliver Strimpel

Let's talk about the commercial extraction of lithium. Do we extract it from all three of the contexts you mentioned? Pegmatite, sedimentary rocks, and brines?

Kathryn Goodenough

At the moment, pretty much all of the world's lithium comes from pegmatites and from brines. The brines are largely mined in South America, particularly in Chile and Argentina, although there is also some brine extraction in other countries, particularly China and the USA. Pegmatites are mined, in particular, in Australia. Again, there is some mining in China, some pegmatites and also a few other countries. Currently we are not extracting any lithium on a commercial basis from sedimentary deposits, although it's looking very likely that that will change quite soon. So particularly in Nevada and in Serbia, there are big and now well-characterised sedimentary deposits that are moving towards development. And also there's currently no commercial-scale extraction of lithium from geothermal brines, but again, that's something that is moving fairly rapidly towards development.

Oliver Strimpel

As our demand for lithium increases dramatically as we expect, certainly within a decade, where is the additional lithium going to come from?

Kathryn Goodenough

So at the moment, it's coming from ramp-up of existing production, more production from the salars in South America and increased production in particular from pegmatites in Western Australia. But it is very likely that we're going to see increasing diversity of the types of deposits that are being mined and the locations of the deposits that are being mined. There are lithium pegmatites on every continent. I don't expect we'll be seeing any mining in Antarctica anytime soon, but I think it's reasonable to think that all other continents will have lithium pegmatites being mined to a reasonable scale within a decade or two. It's very likely that we will see some of these big sedimentary deposits being mined. Certainly Rio Tinto has recently committed quite a lot of money to developing its Jadardeposit in Serbia. And then, of course, the geothermal brines, if the technologies can be developed to do that really well, to actually be able to extract lithium directly from geothermal brines, perhaps in association with geothermal power plants. Then that has the potential to be a really excellent way of obtaining some of our lithium.

Oliver Strimpel

So there is enough lithium out there to meet our projected demand?

Kathryn Goodenough

There is absolutely no shortage of lithium and, what's more, we know many of the places that we could go to mine it. Scarcity of lithium in the crust is not really an issue. The issues that we have at the moment are much more social and  environmental. They're engineering issues. They're economic issues. To actually open a mine takes 10 years. First of all, you have to really understand the resource that you have. You have to bring in investment to get that funded. You have to develop your flow sheets for mineral processing. And you have to find somebody who's willing to buy whatever product it is that you can make, often a mineral concentrate, for example. And to do all of that, to get the investment in line with the setup of the engineering and with all of the environmental permitting and so on, takes a long while. And right now we're expecting lithium demand to increase significantly, but we're not seeing new mines opening at the same rate. So many of the commentators are saying that we might see issues around supply in the short term, which would drive higher prices, which would then drive opening of new mines. So the issues are not anything to do with scarcity. The issues are around how we manage the environmental impacts, how we manage the economics, how we manage the engineering.

Oliver Strimpel

There have been some much publicized cases of lithium ion batteries catching fire, but the problem seems to be overcome. Nonetheless, there is always scope for future improvement in battery capacity, speed of charging, longevity, and so on. Do you think lithium will at some point be displaced by new battery technologies?

Kathryn Goodenough

There is obviously a lot of research going on and a lot of interest in developing new battery technologies. But I think the really important point is that whatever technology is being used, it's going to need raw materials. Whether we need sodium, whether we need vanadium, whether we need lithium, whichever raw materials we use, we're going to need some raw materials, for batteries, for energy storage. And those raw materials, at least at first, are going to have to be mined because there is no other way of producing them. Recycling can become important down the track when there's a lot of batteries in use and available for recycling. But at first we're going to have to mine them. So mining is going to be really important. Whatever technology becomes the leading technology for batteries.

Oliver Strimpel

Kathryn Goodenough, thank you very much. 

Kathryn Goodenough

Thank you, Oliver. It's interesting talking to you.

Oliver Strimpel

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