The oceans hold vast quantities of magnesium, and researchers have now devised a novel approach that could make extracting this valuable mineral more affordable and sustainable directly from seawater.
Magnesium salts serve numerous purposes, including use in dietary supplements, pharmaceuticals, construction materials, and various industrial applications. Currently, most of the world’s magnesium is sourced from mineral deposits found in rocks, which require mining, crushing, and heating—processes that consume significant amounts of energy.
Scientists reporting in ACS Energy Letters have developed an electrochemical system utilizing specially engineered bismuth electrodes that selectively extract magnesium ions from seawater. Since seawater contains magnesium as the second most abundant positively charged ion—after sodium—the potential for large-scale recovery is considerable. However, separating magnesium from sodium is challenging because their concentrations differ greatly; seawater contains much more sodium.
Existing extraction methods often involve chemicals that precipitate magnesium as a solid, which can then be separated. Alternative techniques using electricity have been explored, but these typically depend on costly membranes, increasing overall expenses. This new approach aims to simplify and reduce the cost of magnesium extraction.
The team constructed an electrochemical cell with thin sheets of bismuth. The cell features two channels separated by a membrane—one carrying seawater, the other an electrolyte solution. When an electric current is applied, the bismuth electrodes modulate the local acidity of the seawater, enabling the collection of magnesium as magnesium hydroxide without heavy chemical use.
Switching the electric field’s direction and the flow of liquids transforms the magnesium hydroxide into magnesium chloride, a form with widespread industrial and commercial uses. Repeating this cycle allowed the researchers to concentrate magnesium significantly, increasing its ratio relative to sodium by about eight times, reaching nearly 20 to 1.
This level of selectivity surpasses previously reported membrane-based electrochemical systems. Efficiently separating magnesium from sodium is crucial for turning seawater extraction into a viable commercial process. The researchers also assessed economic aspects, estimating that producing magnesium chloride this way could cost roughly $107 per ton—well below current market prices.
However, this estimate excludes certain additional expenses, such as drying the final magnesium salt, indicating further research and larger-scale testing are necessary to confirm commercial viability.
Beyond supplying magnesium for health, manufacturing, and construction industries, this technology could help diversify and secure supply chains. It also shifts how we view seawater—not merely as a water source demanding desalination but as an abundant resource containing valuable materials.
If scaled successfully, this method could provide a plentiful, sustainable source of magnesium while reducing our dependence on energy-intensive mining and processing techniques.
