"Direct Magnesium Recovery from Ocean Waters Using Bismuth Electrochemistry" ACS Energy Letters
Magnesium supplements are gaining popularity to treat conditions such as insomnia, migraines, and constipation. Most magnesium salts are extracted from rocks by crushing and heating them, which requires a lot of energy. Now, researchers reporting in ACS Energy Letters have developed bismuth electrodes that selectively pull magnesium ions from seawater, another abundant source of the element. They say their electrochemical approach could be more sustainable and less expensive than current methods.
We have traditionally thought of seawater as something to desalinate and protect, but it is an enormous reservoir of valuable resources." - David Kim
Adapted from ACS Energy Letters 2026, DOI: 10.1021/acsenergylett.6c01659
While minerals in rocks contain large amounts of magnesium, this element is also present in the oceans, where it is the second most abundant cation after sodium. "We have traditionally thought of seawater as something to desalinate and protect, but it is an enormous reservoir of valuable resources," says David Kim, the first author of the study. "Seawater represents an essentially limitless yet underutilized reservoir for such resources."
Historically, extracting magnesium from ocean water required chemical additives to precipitate and remove the metal, a method that was honored in a National Historic Chemical Landmark . Scientists have instead experimented with electric fields to pull magnesium salts out of seawater. But thus far, these electrochemical methods have relied on expensive membranes to effectively convert the magnesium ions into a form that can be separated from the large amount of sodium ions in seawater. In previous work, T. Alan Hatton and Kripa Varanasi, who are the corresponding authors on this research, developed bismuth electrodes that change the acidity of seawater, and they wanted to test whether these electrodes could extract magnesium without chemical additives or costly materials.
The researchers built a layered electrochemical cell, with thin bismuth electrode sheets sandwiching two channels separated by a membrane. In tests of the system, the researchers flowed real seawater through one channel and an electrolyte solution through the other, all under an electric field, to collect magnesium hydroxide. By switching the polarity of the electric field and switching the solutions flowing through each channel, they converted magnesium hydroxide to a consumable form, magnesium chloride.
Through an iterative process, the concentration of magnesium from a seawater sample increased by eight-fold and a ratio of 20 to 1 magnesium to sodium ions. The researchers say this result shows the process was more selective than the other electrochemical membrane systems reported thus far.
Finally, the team calculated that producing magnesium chloride with their electrochemical approach would cost around $107 per ton. This is substantially lower than current market prices for magnesium chloride; however, the researchers acknowledge that this figure doesn't account for several post-extraction steps such as drying the salt.
As demand for magnesium salts continues to rise for applications from health care to construction, the team hopes that electrochemistry could provide an economical option to produce this mineral. "If this work similarly excites and inspires even one other person to think about how electrochemistry can transform our available resources into sustainable markets," says Kim, "then we have accomplished something meaningful."
Varanasi concludes, "by turning seawater itself into a source of magnesium, this technology can enable domestic production and make our supply chains for critical materials more robust - moving us toward a blue economy where the ocean becomes a platform for producing the critical materials our industries need."
