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Chemists invent a more efficient way to extract lithium from mining sites, oil fields, used batteries
Chemists at the Department of Energy’s Oak Ridge National Laboratory have invented a more efficient way to extract lithium from waste liquids leached from mining sites, oil fields and used batteries.
To support a circular economy, aluminum hydroxide can extract 37 milligrams of lithium per gram of recoverable sorbent in a single step. Credit: Jayanthi Kumar, Parans Paranthaman and Philip Gray/ORNL, U.S. Dept. of Energy
They demonstrated that a common mineral can adsorb at least five times more lithium than can be collected using previously developed adsorbent materials.
“It’s a low-cost high-lithium-uptake process,” said Parans Paranthaman, an ORNL Corporate Fellow and National Academy of Inventors Fellow with 58 issued patents. He led the proof-of concept experiment with Jayanthi Kumar, an ORNL materials chemist with expertise in the design, synthesis and characterization of layered materials.
“The key advantage is that it works in a wider pH range of 5 to 11 compared to other direct lithium extraction methods,” Paranthaman said.
The acid-free extraction process takes place at 140 degrees Celsius, compared to traditional methods that roast mined minerals at 250 degrees Celsius with acid or 800 to 1000 degrees Celsius without acid.
Lithium is a lightweight metal commonly used in energy-dense and rechargeable batteries. Electric vehicles, which are needed to achieve net-zero emissions by 2050, rely on lithium-ion batteries.
Industrially, lithium is extracted from brines, rocks and clays. The ORNL innovation may help meet rising demand for lithium by making domestic sources commercially viable.
The research reveals a route away from the status quo: a linear economy in which materials from mining, refining or recycling are made into products that, at the end of their lives, are discarded as waste.
The work moves toward a circular economy in which materials are kept in circulation as long as possible to reduce consumption of virgin resources and generation of waste.
The ORNL invention relies on aluminum hydroxide, a mineral that is abundant in Earth’s crust. The scientists used aluminum hydroxide as a sorbent, which is a material that takes up another material — in this case, lithium sulfate — and holds it.
In a process called lithiation, an aluminum hydroxide powder extracts lithium ions from a solvent to form a stable layered double hydroxide, or LDH, phase.
Then in delithiation, treatment with hot water causes the LDH to relinquish lithium ions and regenerate the sorbent. During relithiation, the sorbent is reused to extract more lithium. “This is the basis for a circular economy,” Paranthaman said.
Aluminum hydroxide exists in four highly ordered crystalline polymorphs and one amorphous, or disordered, form. Form turns out to play a big role in the sorbent’s function.
“Based on calorimetric measurements, we learned that amorphous aluminum hydroxide is the least stable form among aluminum hydroxides and thus is highly reactive,” said Kumar. “That was a key to this method resulting in greater lithium extraction capacity.”
Because amorphous aluminum hydroxide is the least stable among the mineral’s forms, it spontaneously reacts with lithium from brine leached from waste clays.
“Only when we did the measurements did we realize that the amorphous form is way, way, way less stable. That is why it is more reactive,” Kumar said. “To gain stability, it reacts very quickly compared to other forms.”
Kumar is optimizing the process by which the sorbent selectively adsorbs lithium from liquids containing lithium, sodium and potassium and goes on to form LDH sulfate.
At the Center for Nanophase Materials Sciences, a DOE Office of Science user facility at ORNL, the researchers used scanning electron microscopy to characterize the morphology of aluminum hydroxide during lithiation.
It is a charged neutral layer that contains atomic vacancies, or tiny holes. Lithium is absorbed at these sites. The size of these vacancies is the key to aluminum hydroxide’s selectivity for lithium, which is a positively charged ion, or cation.
“That vacant site is so small that it can fit only cations the size of lithium,” Kumar said. ”Sodium and potassium are cations with larger radii. The bigger cations don't fit into the vacant site. However, it's a perfect match for lithium.”
The selectivity of amorphous aluminum hydroxide for lithium results in near-perfect efficiency. In a single step, the process captured 37 milligrams of lithium per gram of recoverable sorbent — approximately five times more than a crystalline form of aluminum hydroxide called gibbsite, which was previously employed for lithium extraction.
The first step of lithiation extracts 86% of the lithium in the leachate, or brine, from mining sites or oil fields. Running the leachate through the amorphous aluminum hydroxide sorbent a second time picks up the rest of the lithium. “In two steps, you can fully recover the lithium,” Paranthaman said.
Next, the researchers want to extend the process to extract more lithium and regenerate the sorbent in a specific form.
Now, when the amorphous aluminum hydroxide sorbent reacts with the lithium and is later treated with hot water to remove the lithium and regenerate the sorbent, the result is a structural change in the aluminum hydroxide polymorph from amorphous to a crystalline form called bayerite.
“The bayerite form is less reactive,” Kumar said. “It requires either more time — 18 hours — or more concentrated lithium for it to react, as opposed to the amorphous form, which reacts within 3 hours to pick all the lithium from the leachate solution. We need to find a route to get back to the amorphous phase, which we know is highly reactive.”
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