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Incremental and elemental

In 1808, English chemist Humphry Davy isolated small amounts of magnesium from a mixture that also contained mercury. Davy used electrolysis, a process in which electrical current powers a chemical reaction, to isolate magnesium. But unfortunately, Davy was never able to completely separate magnesium. In 1831, French chemist Antoine Bussy isolated purer samples of magnesium metal from magnesium chloride (MgCl2), a magnesium salt, with the help of highly reactive potassium metal.

This approach foreshadowed later methods of isolating magnesium. But more importantly, it allowed chemists to investigate the properties of elemental magnesium in greater detail. They eventually learned that magnesium is an unusually strong metal � its strength-to-weight ratio exceeds that of both aluminum and steel. But magnesium is brittle, so engineers could not immediately use it in structural applications.

Instead, early applications were primarily chemical. When magnesium metal reacts with oxygen, it releases a lot of energy and produces a bright flash of white light. In the late 1800s, this reaction was used in the first flash photography. Even after the later invention of incandescent light bulbs, this special reaction was unmatched. Magnesium powder was (and still is) used in flares and airborne lights used in war called “star shells.� Additionally, magnesium compounds were used as food additives and in fertilizer.

Commercial magnesium production took off in 1886 when German chemist Robert Bunsen pioneered a way to separate the elements in molten MgCl₂. Germany quietly became the world’s leading supplier into the next century. By the early 1900s, magnesium compounds were valuable reagents for many industries, including reactions used to develop pharmaceuticals. 

Then World War I gripped the world. And with Germany at the epicenter, the world’s supply of the valuable material was cut off. 

Mixtures of metals, called alloys, are fascinating. Properties of alloys can be superior to its components. Combining lightweight magnesium with aluminum creates an alloy that is lighter than aluminum and less brittle than magnesium. The super light and strong alloy was an ideal material for making pistons used in high-performance racing engines. Aircraft, especially warplanes, also benefitted from the high strength-to-weight alloy. Germany used magnesium as a structural material in World War I, so their military aircraft were able to carry heavier bombs because the planes themselves cut weight by switching to magnesium-based alloys. To keep up, the U.S. needed a reliable large-scale source of magnesium.

Fortunately, in 1916, Dow Chemical had already embarked on a path that would eventually revolutionize the metal’s story. That year, at a Midland, Michigan, pilot plant, Dow created its first block of pure elemental magnesium. The process involved electrolyzing a molten MgCl₂ bath, which resulted in magnesium metal and chlorine gas. 

The feedstock was concentrated brine present under Midland. While MgCl₂ was present in the brine, so was NaCl at a much higher concentration, so chemical processing was required to isolate MgCl₂. Calcium oxide was used to react and result in solid Mg(OH)₂, which was collected and further reacted with hydrochloric acid (HCl) to make pure MgCl₂ for use in electrolysis. 

By 1918, almost 2 tons of magnesium was produced at the Midland facility. Dow next sought to scale up its operation. To do so, it would have to change the feedstock from magnesium-rich brine to a virtually bottomless � and less concentrated � feedstock of seawater.

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Sustaining magnesium

Despite the end of Dow’s mission to make magnesium from seawater, worldwide demand is still high. Others look to seawater as a source again, and startups are looking to the process as a clean, flexible way to make the valuable material. Much of the output is used to replace materials such as steel in the automobile industry to create light-weight cars. Light cars are efficient, and they are believed to handle better on the road. According to the International Magnesium Association, the metal appears in gearboxes, steering columns, air bag housings, steering wheels, seat frames, fuel tank covers, and other components.

But there’s a limit to how much magnesium engineers can substitute into cars and aircraft. Magnesium is more expensive than aluminum, and despite its natural abundance, engineers have struggled to make structural parts with enough strength at low costs. Further research is ongoing, however. In 2017, scientists from Pacific Northwest National Laboratory developed a new process to incorporate magnesium into load-bearing components. It reports: “Using our process, we have enhanced the mechanical properties of magnesium to the point where it can now be considered instead of aluminum for these applications � without the added cost of rare-earth elements.� Materials scientists hope to develop more breakthroughs in low-cost alloys and coatings for future applications, such as thermal coatings that are more resilient in space.

Today, most commercial magnesium comes from China, which produces nearly 2 million metric tons per year � almost 20 times more than the U.S. Most of China’s magnesium production is powered by coal and produced from a magnesium-rich rock called dolomite. 

It uses the Pigeon Process, named for the inventor not the bird. The magnesium source is dolomite, a mixed calcium-magnesium carbonate mineral. When heated, it releases CO₂ gas and produces magnesium oxide. At high temperatures, MgO is reduced, resulting in vapor, which condenses and is collected as metallic magnesium. Thermal energy and electricity in China are both supplied from coal. Making 1 ton of magnesium requires 8 to 12 tons of coal. Coal is cheap, and low-cost magnesium from the Pigeon Process largely pushed other manufacturers out of the market.

But this emissions-heavy process may not lead the way forever. China recently underwent a magnesium shortage due to caps on carbon emissions. There were claims that the shortage threatened the global car industry. And as more companies, governments, and individuals call for sustainable manufacturing, the large-scale electrochemical approach to magnesium production developed by Dow looks more attractive by comparison. 

Decades ago, clean magnesium revolutionized how technology was built. Cars, planes, satellites, and electronics all benefited from alloys of the abundant metal. Now, looking toward a future where sustainability is a top priority, the old clean technology may be poised to return.

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