People have been taking salts from the ocean, like table salt, since ancient times. Although seawater is a rich source of various minerals, researchers are investigating which ones they can extract from the ocean. While table salt is the most accessible, magnesium is one of those minerals that is prevalent in the sea and is becoming more and more useful on land.
Magnesium is being used in a growing number of environmentally friendly products, such as low-carbon cement, next-generation batteries, and carbon capture. These uses are refocusing interest in domestic magnesium production. Currently, salt lake brines, some of which are threatened by droughts, are used in an energy-intensive process in the United States to produce magnesium. Magnesium was listed by the Department of Energy in its recently published list of essential components for domestic production.
An easy method to separate a pure magnesium salt, a feedstock for magnesium metal, from seawater has been discovered by scientists at Pacific Northwest National Laboratory (PNNL) and the University of Washington (UW), according to a paper published in Environmental Science & Technology Letters. Their novel approach produces a long stream of two solutions flowing side by side. The technique, known as the laminar coflow method, makes use of the boundary that is continuously reacting as a result of the flowing solutions. The system never achieves balance as new solutions are constantly being introduced.
This technique uses an established procedure in a novel way. Chemical companies successfully produced magnesium feedstock from seawater in the middle of the 20th century by combining it with sodium hydroxide, also known as lye. The resulting magnesium hydroxide salt was then processed to create magnesium metal, which is what gives the antacid milk of magnesia its name. However, the method yields a complicated mixture of magnesium and calcium salts that is difficult and expensive to separate. Recent research has yielded pure magnesium salt, allowing for more effective processing.
According to PNNL chemist and UW Affiliate Professor of Materials Science and Engineering Chinmayee Subban, “People typically advance separation research by developing more complicated materials.” “This work is so exciting because we’re adopting an entirely new strategy. We discovered an easy method that functions. By producing primary feedstock, this process, when scaled, may contribute to the revival of magnesium production in the United States. A vast, blue, untapped resource surrounds us. ”
Water to crystalline salt conversion
Using seawater from the PNNL-Sequim campus, Subban and the group tested their new technique. This allowed the researchers to utilize PNNL resources all over Washington State.
As Subban explained, “As a member of the Coastal Sciences staff, I just called a member of our Sequim chemistry team and requested a seawater sample.” “We had a cooler shipped the following day to our lab in Seattle. We discovered ice packs and a bottle of frigid Sequim seawater inside. ” This project is an example of how the Richland, Seattle, and Sequim campuses of PNNL can work together.
With the laminar coflow technique, the researchers circulate seawater alongside a hydroxide-containing solution. Seawater that contains magnesium reacts quickly to produce a layer of solid magnesium hydroxide. This thin layer prevents the solution from mixing.
According to PNNL postdoctoral researcher Qingpu Wang, “The flow process produces dramatically different results than simple solution mixing.” “Calcium cannot interact with magnesium hydroxide because of the initial solid magnesium hydroxide barrier. Without the need for additional purification procedures, we can selectively produce pure solid magnesium hydroxide.
This method’s power comes from how selective it is. Researchers can avoid steps that take a lot of energy and cost a lot of money to clean by making pure magnesium hydroxide that is not contaminated with calcium.
Future-oriented sustainability
The innovative and gentle process has strong potential for sustainability. For instance, using seawater and marine renewable energy, the sodium hydroxide needed to extract the magnesium salt can be produced locally. Desalination of seawater requires a pre-treatment that involves the removal of magnesium. By combining the new method with already-existing technologies, it might be simpler and less expensive to convert seawater to freshwater.
The team is especially enthusiastic about the process’ potential. In their work, the laminar coflow method for selective separations is being used for the first time. There are numerous additional potential uses for this novel strategy, but more research is necessary to comprehend the chemistry behind the process. The knowledge gap gives researchers new ways to look into ways to help the blue economy.
PNNL materials scientist Elias Nakouzi said, “We want to move this work from the empirical to the predictive.” There is an exciting chance to gain a fundamental understanding of how this process works while using it to solve significant issues like developing new energy materials and selectively separating ions that are difficult to separate for the treatment of water and resource recovery.
The PNNL Laboratory Directed Research and Development program funded the published study. The study’s other co-author was Elisabeth Ryan of the UW. Under the Marine Energy Seedlings Program, the Office of Energy Efficiency and Renewable Energy, Water Power Technologies Office, of the Department of Energy is paying for the development of this technology right now.
