Breakthrough in High-Purity Magnesium: Removing Aluminum Impurities Using Furnace Scale – A Low-Cost Industrial Solution

Researchers at Xi’an Jiaotong University have pioneered a novel magnesium purification strategy that efficiently and affordably removes aluminum impurities under industrial conditions, enabling large-scale production of low-aluminum high-purity magnesium. The technology is already deployed on commercial production lines.

Magnesium is a critical strategic metal with wide applications in lightweight transportation, high-end metal reduction (e.g., titanium, zirconium), and biomedical devices. About 80% of the world’s primary magnesium is produced via the silicothermic process, which offers cost and scale advantages but suffers from high and fluctuating impurity levels — especially aluminum. Aluminum content can vary between 21–845 mg/kg across production batches, a >32-fold swing spanning five purity grades. This instability limits magnesium’s use in electronics-grade titanium, nuclear-grade zirconium, and medical implants, while eroding profitability for producers.

In 2023, the team identified the root cause: during silicothermic reduction, aluminum predominantly exists as gaseous aluminum fluoride (AlF3), which co-condenses with magnesium. After analyzing furnace wall scale deposits, they hypothesized that calcium oxide (CaO) could effectively remove aluminum.

First author Zheng Rui (Ph.D. candidate at Xi’an Jiaotong University) confirmed that adding CaO reduced aluminum levels from ~109.5 mg/kg to just 6.3 mg/kg — a removal efficiency exceeding 90%. Working with major raw magnesium producer Teda Coal Chemical, and leveraging the Shaanxi Provincial Magnesium-based New Materials Pilot Base, the team quickly validated the method industrially. After iterative optimization, they replaced CaO with calcined dolomite (a mixture of CaO and MgO), a lower-cost, recyclable material commonly used in magnesium smelting. The proportion of magnesium meeting high-purity Mg9998 standard (ultra-low aluminum) jumped from near 0% to 83.3%, transforming “accidental success” into “stable production.”

Cost analysis shows this purification method reduces expenses by approximately 96% compared to mainstream vacuum distillation, offering a practical pathway for low-cost, large-scale production of low-aluminum high-purity magnesium.

“The economic gains are significant, but what excites us more is the chain reaction across the entire value chain,” says Prof. Shan Zhiwei, corresponding author of the study published in Nature Materials. “Aluminum in magnesium is not always metallic — some exists as compounds like AlF3. These act as ‘invisible troublemakers’ that carry over into downstream products.”

For example, in titanium sponge production (critical for electronics-grade titanium), magnesium is used as a reducing agent. If raw magnesium contains uncontrolled aluminum, the aluminum transfers into titanium and is extremely difficult to remove, ruining chip-grade titanium. In biomedical applications, high aluminum in degradable magnesium bone screws may accumulate in the human body and increase Alzheimer’s risk. “Reducing aluminum is a huge benefit for medical devices as well,” Shan emphasizes.

Contrary to a common belief that “aluminum in raw magnesium doesn’t matter for aluminum-containing magnesium alloys,” the team’s latest unpublished experiments show that even trace aluminum (<0.01 wt.%) significantly degrades pure magnesium’s corrosion resistance. “We are preparing this finding — we believe the entire magnesium alloy field will benefit from it,” Shan says. Beyond profit margins, the technology improves downstream titanium, electronics, and biomedical industries, likely prompting revisions to industry standards.

The key to cracking this industrial challenge was the right mindset. The team noticed a puzzling anomaly: magnesium produced on the same day showed wildly fluctuating aluminum levels, even though raw materials, operators, and process conditions were stable. “That didn’t make logical sense,” Shan recalls.

That “why” drove them to the production floor. An old saying goes: “For the deadliest poison, the antidote lies within seven steps.” In research, the most frustrating industrial problems often hide their solutions in the most mundane production details. Workers struggled daily with a hard scale layer forming at the mouth of magnesium reduction reactors — like limescale in a kettle. This “annoying scale” had to be removed manually every day, consuming labor and affecting heat transfer. When the team analyzed the scale, they found a stable “calcium-aluminum-fluoro-oxide” compound.

Combined with their prior knowledge that aluminum impurity arrives as AlF3, the insight struck: if the scale already concentrates calcium, fluorine, aluminum, and oxygen, could they intentionally use calcium oxide to “capture” aluminum from AlF3, converting it into a stable scale compound and thereby separating aluminum from magnesium? Like using a magnet to attract iron filings, CaO became the key “aluminum adsorbent.” The principle seems simple, but only after a decade of mechanistic studies and industrial experience could the team see the clue hidden in the despised furnace scale.

What thrilled them most was the moment of clarity: the scale that workers hated and spent hours scraping away actually held the core secret to solving aluminum fluctuations. Inspired by this, the team has extended the approach to control other impurities in magnesium, offering a new paradigm for metal purification.

Prof. Shan emphasizes that the most impressive outcome of this research is not a single technical breakthrough but the “antidote within seven steps” mindset — finding answers on the factory floor and seeking solutions from the problem itself. This methodology can guide similar industrial technology challenges.