How engineers extract lithium from seawater and brine

HostIt's easy to take for granted the little glass and metal slab in my pocket, but that phone only works because of a soft, silvery metal hidden away in some of the harshest places on earth. We're seeing a massive push for lithium right now, but the way we get it's changing fast.

HostMost people think of mining as digging big holes in the ground, but for lithium, we're often just looking at water, right?

GuestThat's the big shift. For a long time, if you wanted lithium, you went to places like the high deserts in South America. Underneath these giant, flat salt crusts, there are huge pools of very salty water called brine. This water is packed with minerals. To get the lithium out, engineers pump that water up to the surface and fill these massive ponds that stretch for miles. Then, they just let the sun and the wind do the work. The water dries up over a year or two, and the salts get thicker and thicker until they can pull the lithium out. It's basically a giant game of waiting for the weather to help you.

HostBut we're building cars and phones way faster than water can dry out in the sun. If it takes two years just to get the raw stuff, that feels like a huge bottleneck for the whole world.

GuestIt's a massive bottleneck. Plus, it's not very clean. When you pump all that water up and let it dry away into the air, you're losing millions of gallons of water in places that are already bone dry. It can mess with the water table for the people living nearby. So, engineers are working on a new way called direct extraction. Think of it like a very smart Brita filter. Instead of waiting for the water to dry up, you run the salty brine through a machine filled with special beads or tiny tubes. These beads are designed to act like a lock that only fits one key, and that key is lithium. The lithium sticks to the beads, and the rest of the salty water just passes through and can be pumped right back underground.

HostSo you're saying we can skip the two year wait and just grab the metal as the water flows by? That sounds almost too easy. Why has it taken so long to start doing this?

GuestThe chemistry is actually really tricky. Brine is a messy soup of different metals. You have got lots of sodium and magnesium in there, and they're all fighting for space. Magnesium is the big problem because its atoms are almost the exact same size as lithium atoms. If your filter isn't perfect, it gets clogged up with the wrong stuff. Engineers have had to build these special materials at a tiny, molecular level to make sure they only grab what they want. It's only recently that the tech has become cheap enough and tough enough to work at a big scale. But even then, we're still just talking about the salt flats. The real dream is the ocean.

HostI was going to ask about that. The ocean is full of salt, so I assume it's full of lithium too. If we can pull it out of desert water, why are we not just sticking these filters in the sea?

GuestThe scale is the problem. In the desert pools, the lithium is pretty thick. But in the ocean, it's spread out so thin it's almost hard to wrap your head around it. If you took a million drops of seawater, only a tiny fraction of one drop would be lithium. It's like trying to find a few specific grains of red sand in a whole beach of white sand. To get enough lithium for just one car battery, you would've to process enough seawater to fill thousands of Olympic swimming pools. The energy it would take to pump that much water through a filter would cost way more than the lithium is worth.

HostSo the ocean is just a giant tease then? We know it's there, but we can’t touch it?

GuestNot necessarily. Engineers are trying to find ways to make the lithium come to us. One idea is called electrochemical pumping. Instead of using a filter, you use two plates that carry an electric charge. You dip them into the seawater, and the charge pulls the lithium ions toward the plates like a magnet. Then you flip the switch, and the plates spit the lithium out into a separate tank. Another group of researchers is looking at using the natural flow of the ocean. They're designing long, wavy fibers that look like seaweed. You just let them sit in the ocean currents, and as the water flows over them, the lithium sticks to the fibers. Every few weeks, you pull the seaweed up, rinse off the lithium, and drop it back in.

HostHmm, that sounds like a much better deal if the ocean is doing the pumping for you. But even with the seaweed idea, it still sounds like we're years away from the ocean powering our phones. Is any of this actually happening yet?

GuestWe're seeing the first big tests right now. There are pilot plants in places like the Salton Sea in California and projects in the works across the Middle East. They're trying to see if these filters and electric pumps can survive the salt and the heat for years at a time. The stakes are huge because there's enough lithium in the ocean to power every car on earth for thousands of years. We just have to get better at picking that one specific needle out of the world’s biggest haystack.

HostEven if it's spread thin, the sheer amount of water in the sea means we're sitting on a nearly endless supply of energy.

GuestThe ocean holds about one hundred and eighty billion tons of lithium, which is tens of thousands of times more than all the mines on land combined.

HostThe battery in my pocket started as a slow soak in a desert pond, but it looks like the future of that power is going to come from learning how to sift through the waves.