Tidal Metals sees seawater as the solution to a critical mineral shortage

Tim De Chant
Updated ·4 min read

Last year, the U.S. designated magnesium as a critical mineral, one of the “electric 18” that are critical for the energy transition. The metal is used in a range of electronics, and it weighs less than aluminum, making it an attractive alternative for automakers.

But like with so many other minerals, China has grown to dominate the market. It’s not because magnesium is scarce — in fact, it’s the eighth most abundant mineral in the Earth’s crust, and it's the third most abundant dissolved mineral in the world’s oceans. But in the U.S., at least, only one company produces virgin metal -- everything else is either imported or recycled from scrap.

“The name of the game really is, can you compete with the 90% production that’s coming out of China today?” said Howard Yuh, co-founder and CEO of Tidal Metals.

Yuh is betting that his startup can. The company, previously known as GreenBlu, had been working on desalination technology when it realized there was more value in the minerals that were left behind.

“At that time, the industry around magnesium was already sort of in shambles in the United States,” he said. Sensing opportunity, in late 2023 the company pivoted to magnesium production and rebranded.

The lightweight metal has the potential to significantly reduce carbon emissions from transportation if it can be produced with minimal pollution. Motorsports fans will note that magnesium is common in race cars, particularly in the wheels, where every pound lost improves acceleration and handling. In passenger vehicles, broader use of magnesium would improve fuel economy, reducing the carbon footprint of fossil fuel vehicles and extending the range of electric vehicles. Some battery companies have begun to explore using the metal to improve energy density.

Magnesium today is largely produced in two ways: by cooking the mineral dolomite and by evaporating salt water, usually in giant open-air ponds, and processing what remains. The former is widely used in China and dominates production; it’s also incredibly polluting, especially when coal is the heat source.

Tidal Metals follows the latter, the evaporative approach, but it eschews the ponds. In its place, it uses what’s known as a temperature-swing vapor pump. Basically, the company uses a material that readily absorbs moisture to evaporate seawater or brines leftover from desalination. The material is similar to the silica gel packets you find tucked in things made overseas, and it sits inside a box that’s exposed to seawater. When the material becomes saturated, Tidal Metals closes the box and raises the temperature, releasing the water.

Meanwhile, another material-filled box opens to continue evaporating the seawater. Once that box is saturated, Tidal Metals uses heat pumps to move the heat from the first box, which is now drier, to the second, saturated box. Apart from the initial heat needed to warm the first box, Yuh said the process is very efficient. “We’ve basically recycled about 97% of the energy.”

In the end, the startup will have evaporated a metric ton of seawater to produce about 4 kilograms of the magnesium salt.

Once the water is evaporated, some H2O molecules are still bound to the magnesium chloride. Those need to go, too. Yuh wouldn’t disclose details, but he said the company has tweaked an existing process to make it easier.

Tidal Metals is working on a pilot plant that can produce 200 tons per year. Funding for the project comes from a recent $8.5 million seed round led by DCVC with participation from Bidra Innovation Ventures and First Spark Ventures. Once the engineering on that plant is sorted, Yuh said the startup is aiming for a larger-scale facility that can produce 10,000 tons per year, possibly as early as 2026.

Altogether, Tidal Metals’ process promises to be significantly less polluting than what’s done in China, particularly if renewable electricity is used to power the heat pumps. Plus, because the company can use seawater and briny waste from desalination plants, the resource is nearly unlimited, unlike magnesium that comes from mined dolomite.

“The one desalination plant in San Diego pumps in 100 million gallons of seawater a day. That’s enough to supply all of the U.S. with magnesium — 180,000 tons a year,” Yuh said. “Today, it’s all going to waste.”

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