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PNNL process extracts magnesium salt from seawater using laminar coflow

Researchers from Pacific Northwest National Laboratory (PNNL) and the University of Washington (UW) have developed a simple way to isolate a pure magnesium salt, a feedstock for magnesium metal, from seawater. The new method flows two solutions side-by-side in a long stream. Called the laminar coflow method (LCM), the process takes advantage of the fact that the flowing solutions create a constantly reacting boundary. Fresh solutions flow by, never allowing the system to reach a balance.


Wang et al.

A paper on their work is published in Environmental Science & Technology.

Here, we show that the nonequilibrium conditions in LCM achieved using a microfluidics device and by simply coinjecting a NaOH solution with seawater can result in improved selectivity for Mg(OH)2 unlike in a conventional bulk mixing method. The resulting precipitates are characterized for composition, and the process yield and purity are optimized through systematic variations of the reaction time and the concentration of NaOH. This is the first demonstration of LCM for selective separation, and as a one-step process that does not rely on novel sorbents, membranes, or external stimuli, it is easy to scale up. LCM has the potential to be broadly relevant to selective separations from complex feed streams and diverse chemistries, enabling more sustainable materials extraction and processing.

—Wang et al.

In the mid-20th century, chemical companies successfully created magnesium feedstock from seawater by mixing it with sodium hydroxide, commonly known as lye. The resulting magnesium hydroxide salt, which gives the antacid milk of magnesia its name, was then processed to make magnesium metal. However, the process results in a complex mixture of magnesium and calcium salts, which are hard and costly to separate. This recent work produces pure magnesium salt, enabling more efficient processing.

PNNL chemist and UW Affiliate Professor of Materials Science and Engineering Chinmayee Subban and the team tested their new method using seawater from the PNNL-Sequim campus, allowing the researchers to take advantage of PNNL facilities across Washington State.

In the laminar coflow method, seawater flows alongside a solution with hydroxide. The magnesium-containing seawater quickly reacts to form a layer of solid magnesium hydroxide. This thin layer acts as a barrier to solution mixing.


The laboratory-scale flow device for extracting magnesium salt. (Photograph courtesy of Qingpu Wang | Pacific Northwest National Laboratory)

The selectivity of this process makes it particularly powerful. Generating pure magnesium hydroxide, without any calcium contamination, allows researchers to skip energy-intensive and expensive purification steps.

The new and gentle process has the potential to be highly sustainable. For example, the sodium hydroxide used to extract the magnesium salt can be generated on site using seawater and marine renewable energy. Removing magnesium is a necessary pre-treatment for seawater desalination. Coupling the new process with existing technologies could make it easier and cheaper to turn seawater into freshwater.

This new approach has many additional potential applications, but more work needs to be done to understand the underlying chemistry of the process.

The published study was supported by the PNNL Laboratory Directed Research and Development program. Elisabeth Ryan of UW was also a co-author of the study. Current development of this technology is supported by the Department of Energy, Office of Energy Efficiency and Renewable Energy, Water Power Technologies Office under the Marine Energy Seedlings Program.


  • Qingpu Wang, Elias Nakouzi, Elisabeth A. Ryan, and Chinmayee V. Subban (2022) “Flow-Assisted Selective Mineral Extraction from Seawater” Environmental Science & Technology Letters 9 (7), 645-649 doi: 10.1021/acs.estlett.2c00229



Very interesting process; I wonder if it could be used to extract seawater lithium, as there is a seemingly infinite supply there.

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