New electrodes can extract magnesium from seawater to secure US supply chains

The world got its magnesium mostly by blowing up rocks for a long time. Mining required pulverizing ore and blasting massive kilns with energy. Extracting trace amounts of metal meant pouring tons of chemical additives into ocean brine. Overall, the method was extreme and expensive, but it supplied the world with a critical mineral that powers so many things from concrete to sleep gummies. Now, two MIT engineers want to replace that whole destructive circus with a gentle electric pulse. Researchers have developed a sustainable electrochemical method using bismuth electrodes to extract magnesium directly from seawater. The method is an abundant alternative to existing, energy-intensive rock mining and additive-heavy ocean extraction. Driven by rising demand across healthcare and construction, the team hopes electrochemistry will deliver an economical way to produce magnesium. “We have traditionally thought of seawater as something to desalinate and protect, but it is an enormous reservoir of valuable resources,” said David Kim, the first author of the study. “Seawater represents an essentially limitless yet underutilized reservoir for such resources.” Mining the ocean for magnesium Magnesium ranks as the eighth most abundant element in the Earth’s crust and the third most plentiful dissolved in seawater. Despite the abundance, most supply is dominated by China. Seawater is packed with minerals, but it is dominated by sodium. Typically, separating the two required complex filter membranes that clogged easily and ballooned operational costs. The new system aims to overcome this challenge. Researchers T. Alan Hatton and Kripa Varanasi have built a layered electrochemical cell that extracts high-purity magnesium directly from raw seawater using custom bismuth electrodes. This technique overcomes the use of costly polymer membranes and harsh chemical precipitants. Interestingly, it pulls pure magnesium chloride from ordinary ocean water for an estimated baseline cost of $107 per ton — a absolute fraction of prevailing market prices. The development centers on selectivity. Researchers line micro-channels of seawater with thin bismuth electrodes and apply a precise electric field to temporarily shift the water’s local acidity. This subtle chemical change forces magnesium ions to separate out as solid magnesium hydroxide. By running real seawater through one channel and an electrolyte through the other under an electric field, magnesium hydroxide was captured. Reversing the electric current’s polarity and adjusting fluid flow automatically redissolves the precipitate into liquid magnesium chloride. Each pass through this cycle continually multiplies the total yield. Strengthening the supply Through iterative cycles, the system achieved an eightfold spike in concentration and a 20-to-1 ratio of magnesium to sodium ions, outperforming every rival electrochemical system on record. Demand is soaring. Constipation remedies, insomnia supplements, and lightweight industrial alloys are all competing for the same limited supply. Magnesium is the lightest structural metal. Combined with aluminum, it creates ultra-lightweight, high-strength alloys for car parts, aircraft bodies, and high-performance bicycles to improve fuel efficiency. While the $107-per-ton estimate leaves out post-extraction drying costs, the core economics remain staggering. If scaled, it turns the ocean from a entity we merely protect into a silent, self-replenishing factory for critical minerals. “If this work similarly excites and inspires even one other person to think about how electrochemistry can transform our available resources into sustainable markets,” noted Kim, “then we have accomplished something meaningful.” Through seawater extraction, this technology strengthens supply chains, boosts domestic production, and supports a blue economy that turns ocean resources into critical industrial materials. The study was published in the ACS Energy Letters. Get the latest in engineering, tech, space & science - delivered daily to your inbox.Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her work has been featured in well-known publications including Nature India, Supercluster, The Weather Channel and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.