Princeton Pulls Lithium From Slag Using Only Air

Princeton researchers recover up to 96% of lithium from mining slag by exploiting a single chemical property: its appetite for moisture

27 Mar 2026

For years, the lithium industry has left enormous salt waste piles sitting in the desert sun. The leftover slag from brine mining contains around one percent lithium by weight, and nobody had found a cost-effective way to get it out. A Princeton University team just did, using only air.

Published in Nature Communications in March 2026, the method exploits a property of lithium chloride that turned out to be hiding in plain sight. Unlike competing salts, lithium chloride absorbs atmospheric moisture far more aggressively. When slag is exposed to controlled relative humidity between 12 and 30 percent, the lithium chloride draws in enough ambient water vapor to liquefy, pulling away cleanly from dry surrounding salts like halite, sylvite, and gypsum. No acids, no added water, no heat.

The results were difficult to argue with. The team recovered up to 96 percent of lithium in test materials, reaching concentrations of 97,000 parts per million, well above the threshold for battery-grade manufacturing. The phase change is thermodynamically spontaneous, meaning the system self-selects for lithium without any external energy nudge. The process takes minutes to hours rather than the months conventional evaporation methods require.

"This research seems quite straightforward, but nobody had done it before," said Prof. Zhiyong Jason Ren, who leads the group at Princeton's Andlinger Center for Energy and the Environment. Ren co-founded Princeton Critical Minerals, a startup working to advance related technologies toward commercial deployment.

The method remains at bench scale, and applying it across sprawling outdoor slag piles in the field will require meaningful engineering work. Variations in slag composition across North American brine operations also need further characterization. But for an industry under growing pressure to squeeze more lithium from fewer resources, a process that recovers critical material from what was once considered worthless waste, powered entirely by the humidity in the air, points toward a supply chain that wastes a lot less than the current one does.