Saline solution-based method efficiently recovers critical minerals from e-waste

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory have developed a method for selectively recovering manganese, magnesium, dysprosium, and neodymium from spent electronics.

Using a simple mixed-salt water-based solution and their knowledge of metal properties, the team was able to separate critical minerals in continuously flowing reaction chambers.

The method, detailed in two complementary research articles and presented at the 2024 Materials Research Society (MRS) Spring Meeting in Seattle, is based on the behaviour of different metals when placed in a chemical reaction chamber where two different liquids flow together continuously. The research team exploited the tendency of metals to form solids at different rates over time to separate and purify them.

The group first reported in February 2024 successfully separating two essential rare earth elements, neodymium and dysprosium, from a mixed liquid. The two separate and purified solids formed in the reaction chamber in four hours, versus the 30 hours typically needed for conventional separation methods.

The two critical minerals are used to manufacture permanent magnets found in computer hard drives and wind turbines, among other things. Until now, separating these elements with very similar properties has been challenging. The ability to economically recover them from e-waste could open up a new market and source of these key minerals.

Mine waste and salty water as a source of magnesium

Recovering minerals from e-waste is not the only application for this separation technique. The research team is exploring the recovery of magnesium from seawater as well as from mining waste and salt lake brines.

“Next, we are modifying the design of our reactor to recover a larger amount of product efficiently,” lead researcher Qingpu Wang said in a media statement.

Using a complementary technique, Wang and his colleague Elias Nakouzi also showed that they can recover nearly pure manganese (>96%) from a solution that mimics dissolved lithium-ion battery waste. Battery-grade manganese is produced by a handful of companies globally and is used primarily in the cathode, or negative pole of the battery.

In this study, the research team used a gel-based system to separate the materials based on the different transport and reactivity rates of the metals in the sample.

“The beauty in this process is its simplicity,” Nakouzi said. “Rather than relying on high-cost or specialty materials, we pared things back to thinking about the basics of ion behaviour. And that’s where we found inspiration.”

The team is expanding the scope of the research and will be scaling up the process through a new PNNL initiative, Non-Equilibrium Transport Driven Separations (NETS), which is developing environmentally friendly new separations to provide a robust, domestic supply chain of critical minerals and rare earth elements.

“We expect this approach to be broadly relevant to chemical separations from complex feed streams and diverse chemistries—enabling more sustainable materials extraction and processing,” said Nakouzi.