How Does Li Behave Around Fe-Oxides?

Did you know that lithium (Li) can change hands with iron oxides? Let's dive into how this happens and why it matters. In our vast world, weathering processes shape the climate. One way to track these processes is by looking at lithium isotopes. Scientists tend to focus on how Li sticks to or gets absorbed into clay minerals. But there's a parallel story with Fe-oxides that's worth exploring. We did some lab experiments to see how Li behaves when it meets different Fe-oxides like goethite, hematite, wüstite, and magnetite. Here's what we found: Poorly crystallized goethite nanoparticles, with a point of zero charge around 7. 7, can grab about 20% of dissolved Li from pH levels 4 to 10. Once the pH hits around 12, it can gobble up to 90% of the Li. But well-crystallized Fe-oxides barely touch the stuff.

Why's that? It seems like the poorly crystallized goethite goes through some dissolution and re-precipitation at its surface. That's where the magic happens. In this process, goethite is choosy. It prefers the lighter 6 Li isotopes, leaving behind a fractionation trail of Δ 7 Li oxide-fluid around -16. 7 to -20. 1‰. This all gives us a peek into what goes on in highly weathered soil and sediments rich in Fe-oxides, like laterites. It also shines a light on the chemistry that happens at mineral surfaces during water interactions. Plus, it could help us figure out large-scale Li extraction for the future.

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