By Beth Mundy
Magnesium has emerging sustainability-related applications, including in carbon capture, low-carbon cement, and potential next-generation batteries. These applications are bringing renewed attention to domestic magnesium production. Currently, magnesium is obtained in the United States through an energy-intensive process from salt lake brines, some of which are in danger due to droughts. The Department of Energy included magnesium on its recently released list of critical materials for domestic production.
A paper published in Environmental Science & Technology Letters shows how researchers at Pacific Northwest National Laboratory (PNNL) and the University of Washington (UW) have found a simple way to isolate a pure magnesium salt, a feedstock for magnesium metal, from seawater. Their new method flows two solutions side-by-side in a long stream. Called the laminar coflow method, the process takes advantage of the fact that the flowing solutions create a constantly reacting boundary. Fresh solutions flow by, never allowing the system to reach a balance.
This method plays a new trick with an old process. In the mid-20th century, chemical companies successfully created magnesium feedstock from seawater by mixing it with sodium hydroxide, commonly known as lye. The resulting magnesium hydroxide salt, which gives the antacid milk of magnesia its name, was then processed to make magnesium metal. However, the process results in a complex mixture of magnesium and calcium salts, which are hard and costly to separate. This recent work produces pure magnesium salt, enabling more efficient processing.
“Normally, people move separations research forward by developing more complicated materials,” said PNNL chemist and UW Affiliate Professor of Materials Science and Engineering Chinmayee Subban. “This work is so exciting because we’re taking a completely different approach. We found a simple process that works. When scaled, this process could help drive the renaissance of U.S. magnesium production by generating primary feedstock. We’re surrounded by a huge, blue, untapped resource.”
From Sequim water to solid salt
Subban and the team tested their new method using seawater from the PNNL-Sequim campus, allowing the researchers to take advantage of PNNL facilities across Washington State.
“As a Coastal Sciences staff member, I just called a member of our Sequim chemistry team and requested a seawater sample,” said Subban. “The next day, we had a cooler delivered to our lab in Seattle. Inside, we found cold packs and a bottle of chilled Sequim seawater.” This work represents the collaboration that can happen across PNNL’s Richland, Seattle, and Sequim campuses.
In the laminar coflow method, the researchers flow seawater alongside a solution with hydroxide. The magnesium-containing seawater quickly reacts to form a layer of solid magnesium hydroxide. This thin layer acts as a barrier to solution mixing.
Pacific Northwest National Laboratory draws on its distinguishing strengths in chemistry, Earth sciences, biology and data science to advance scientific knowledge and address challenges in sustainable energy and national security. Founded in 1965, PNNL is operated by Battelle for the Department of Energy’s Office of Science, which is the single largest supporter of basic research in the physical sciences in the United States. DOE’s Office of Science is working to address some of the most pressing challenges of our time. For more information, visit https://energy.gov/science. For more information on PNNL, visit PNNL’s News Center. Follow us on Twitter, Facebook, LinkedIn and Instagram.