Everybody these days knows something about lithium. We know it’s a vital ingredient in the batteries that power the machines we rely on every day: cellphones, laptop computers, electric cars. But most people have no idea where it comes from.
Lithium is typically mined from briney lakes in a time-consuming and energy-intensive process. Major producers are in South America, Australia, China and Africa. There’s only one source in the United States: a dry lakebed south of Las Vegas, Nevada.
In reality, lithium is all around us. It’s found in seawater across the planet, and in groundwater in certain geologic formations. But the concentrations are low, and no economically sound methods have been found to extract it.
Now there’s a solution in the works that could yield large quantities of lithium as a byproduct of seawater desalination. The process is being developed by researchers at Monash University in Australia and the University of Texas at Austin. It uses something called a metal-organic framework (MOF) – a sponge-like complex of materials with special filtering properties. (Water Deeply recently reported on a MOF that extracts water from desert air.)
With lithium currently worth about $100 a pound, it could significantly offset the high cost of seawater desalination, helping produce important new supplies of freshwater for a thirsty planet. It would also work with the briney wastewater generated by oil and gas wells (known as produced water), which is now often injected back underground.
Water Deeply spoke with Benny Freeman, a co-investigator on the project and a professor of chemical engineering at the University of Texas.
Water Deeply: How common is lithium?
Benny Freeman: In seawater, I think it’s present at fairly low concentrations. It’s like 1 part per million or less. In the brines around Texas it can be on the order of 1,000 parts per million. That’s got people scrambling right now to map the lithium concentration in oil and gas wells in Texas.
Its rate of use is going up faster than we’re bringing on new sources. So people are looking into a lot of places to find new sources of lithium.
Water Deeply: Is lithium found in all groundwater?
Freeman: It’s a geological question. My understanding is that it’s often found in water that is coming from rock that at some point in the past was associated with volcanic activity. Certainly, that’s the case in Texas. A lot of the places they’re finding lithium are related to geological formations that were volcanically active in the very ancient past. They’re finding it in natural springs in Europe, again associated with rock that has volcanic origin.
Water Deeply: And what are the metal-organic frameworks (MOFs) you are working with?
Freeman: They are very regular crystalline structures and they have large empty spaces in them. The core of these crystals is empty. And then there are windows of a very defined size that connect to the inner core, or the core area, that’s empty. It’s through these very precisely sized windows that anything that’s going to pass through the MOF has to move. It’s a little like if you control a door size in a building, you could size it so that people get in but not horses, or children get in but not adults.
Water Deeply: And how does the device you’re developing extract lithium from water?
Freeman: One of the distinct features of metal-organic frameworks is they have the ability to sort ions that have the same valence, or the same charge on them. This is quite rare in membranes that are used commercially for water purification like desalination. Normally, they are not very good at separating ions that have the same charge, like separating sodium from lithium.
The MOFs have the ability to sort the ions based on their crystal radius, or their bare ion size, which is the opposite of the way polymer membranes work in desalination. In that case, they sort the ions based on the hydrated size. Every ion in water is surrounded by water molecules. Those water molecules typically move with the ion. They are attracted to the ion by the electrical charge on the ion.
A very small ion like lithium, which has a positive charge, will attract a lot of water molecules to it. Although the ion itself is really small, it appears to be really big because it has an entourage of water that it drags around with it. Then, when lithium goes through polymer membranes, it goes through slower than things like sodium or potassium, because it’s dragging all of this water with it.
In the MOFs, it appears the lithium actually sheds its water before it goes through the MOF channel. And in doing so, then it’s the smallest of that series of ions. It goes through faster. Which is really unusual. I would have said it wasn’t possible before I saw the results. It would have been inconceivable to understand how you would do that in a synthetic membrane.
But this is the way biological ion channels work. They sort ions based on the dehydrated size. The ions go through without their entourage of water. This has really not been practiced in synthetic membranes. It’s very unusual.
The way it would work is, you would have these membranes in contact with a solution that would have lithium, salt and other ions, and the lithium would be the fastest ion to go through. So you would enrich it as you pass through the solution. It would selectively pick out lithium. And you get a lot more of the lithium that was in the feedwater itself.
Water Deeply: Is all this theoretical at this point? Or is it working in a laboratory setting?
Freeman: We have not applied it except for a very small sample size on a lab bench. This has not been done in complex feedwaters, and it’s not been done at pilot scale in real water mixtures. These are the things we’re working on now.
Water Deeply: How would it be applied in the setting of a desalination plant?
Freeman: We’re still at a very early point of thinking on this. But the hope would be that they could be used in place of membranes that are used now. Today we don’t recover lithium from produced water, or from seawater for that matter. So this might actually argue for building add-on facilities or separate facilities [at a desalination plant] if you’re going after specific components of interest.
Water Deeply: How much lithium is there in, say, a gallon of seawater?
Freeman: I don’t know the numbers offhand for seawater. But we’re not running out of lithium. We have plenty of it. It’s just not easy to access due to the low concentration in seawater.
We’ve done some calculations based on how much you could get out of produced water [from oil wells], and it’s quite a bit. Essentially, out of one well in a week, from about 4,300 gallons of produced water, you could get enough lithium to make batteries for, like, 1.6 million iPhones or 200 Tesla Model Ss. That’s in a week from a single well. And currently it’s all being pumped back into the ground as wastewater. In a seawater desalination plant, it would go back out to the ocean. So, this would be a little like mining through your garbage and finding gold.
Water Deeply: When will your device be market ready?
Freeman: Right now, we’re looking at several options. The next step is pilot testing, and we’ve had quite a bit of interest from companies interested in helping move it toward market. One of the things we’re trying to do now is to sort out the most efficient pathway toward that goal. I would say we’re several years away. But there’s been an awful lot of interest.