Rare earth metallurgy is a minefield where every deposit rewrites the rules and even tailings can outgrade global projects

Rare earth metallurgy is unlike any other field in mining, and as Damien Krebs told AusIMM’s Metallurgical Society in his webinar Rare Earth Metallurgy 101, every single deposit is a puzzle that defies cookie-cutter solutions.

As Principal Process Consultant at Primero, Damien has built his career across commodities as diverse as uranium, nickel laterites, lithium and base metals. But he made it clear in his talk that nothing compares to the complexity of rare earth elements (REEs).

“The extractive metallurgy of rare earths is the most complicated metallurgy I’ve been involved in,” Damien said. “Every deposit is unique - it’s not just a matter of applying a standard flow sheet. You’re essentially starting a technology development program every time.”

Sixteen elements, one problem: they all behave similarly

The challenge begins with chemistry. There are 16 rare earth elements, and while their industrial applications are vastly different, their chemical behaviour is frustratingly similar. That means separating them into pure, saleable products requires extraordinary effort.

“With gold or copper, you have proven processes you can replicate. With rare earths, there’s no single recipe you can roll out. The differences between elements are subtle, but enough to mean you need bespoke flowsheets for every deposit,” Damien explained.

Compounding the challenge is the mineralogy. Rare earths occur in a wide range of host minerals: bastnäsite in the US, ionic clays in China and Myanmar, monazite and xenotime in mineral sands, or more complex phases like steenstrupine and eudialyte in Greenland. Some are relatively easy to treat; others are refractory, radioactive, or both.

Damien stressed that mineralogy dictates everything. “If you can’t make a high-grade mineral concentrate - say, at least 20 percent rare earth oxide - you’re starting from a difficult position. The downstream processing is expensive, so the less material you put through, the better.”

From clays to hard rock: radically different approaches

The simplest REE source, at least metallurgically, is ionic clays. Here, the elements are loosely adsorbed onto aluminium-rich host minerals like halloysite and gibbsite. In practice, this means cheap, low-acid leaching works well - historically with little environmental oversight in southern China and now increasingly across the border in Myanmar.

The pictures Damien shared told a story of crude operations scarring hillsides and polluting waterways. “For decades, the world got heavy rare earths cheaper than they really should have been,” he said. “The full environmental cost wasn’t charged. That’s changing now, but only slowly.”

Hard rock deposits, by contrast, present an entirely different challenge. Bastnäsite, monazite and xenotime require aggressive processing to liberate REEs from their mineral lattice. Acid baking, caustic cracking, or calcination steps are needed before leaching, each with its own trade-offs.

“For monazite, you can go down the caustic crack route or use acid bake. Acid bake generally gives you higher recoveries and handles xenotime better. But if your concentrate is very high grade and low in silica, a caustic crack can work. It comes down to the mineralogy and impurities - you have to pick carefully.”

The radioactive company they keep

Rare earths themselves are not radioactive. But the minerals they occur with - particularly monazite and xenotime - almost always contain uranium or thorium. Managing these “unwanted companions” is one of the defining hurdles of any REE project.

Damien illustrated this with a cautionary note: “It’s not just uranium or thorium you have to worry about. Their decay products - the daughters - can behave differently. Actinium, for example, is chemically very similar to the rare earths. It will follow them all the way through to intermediate products, creating unexpected hot spots unless you track it carefully.”

This makes permitting and operations fraught. In some jurisdictions, uranium recovery as a by-product is possible; in others, it’s outright banned. Thorium, which has no commercial market, is usually stabilised and diluted into tailings.

“The Lynas example in Malaysia is instructive,” Damien said. “Technically, their tailings were safe, but politics and misinformation made it a flashpoint. The reality is that perceptions can be as important as radiation management itself.”

The scale of separation

Even after beneficiation, cracking, and leaching, the real work is just beginning. The chemical similarities of REEs make them notoriously hard to separate into individual elements. The industry standard is solvent extraction, and it is on a mind-boggling scale.

“To separate 15 rare earths into pure products, you’re looking at around a thousand stages of solvent extraction,” Damien said. “There’s no shortcut. Each element needs to be nudged away from its neighbours, step by step.”

He described rows of mixer-settlers in existing refineries, where kerosene-based organic phases shuttle rare earths across endless extraction, scrubbing and stripping steps. Alternative technologies like ion exchange or electrochemical separation are under research, but none are yet proven commercially.

Tailings as tomorrow’s ore

One of the most thought-provoking points Damien raised was the potential of reprocessing tailings. At Mount Weld, Lynas initially mined ore grading close to 20 percent REO. Even with flotation recoveries in the 60s, the tailings still contain more rare earths than many of the world’s undeveloped deposits.

“The Mount Weld tailings dam will be higher grade than the vast majority of rare earth deposits on the planet,” he noted. “The issue is the fine-grained nature of what’s left. But in the future, when technology improves, it’s a significant resource waiting to be tapped.”

This prospect ties into the broader narrative of critical minerals: securing supply is not just about new mines, but also about rethinking what counts as ore.

Costs, margins, and the economics of complexity

From a cost perspective, Damien was blunt: the most value still comes from the geology. “No metallurgist, no matter how clever, can beat a high-grade deposit in a good jurisdiction with straightforward mineralogy,” he said.

But assuming you have something worth pursuing, the economics hinge on beneficiation. “If you can’t make a high-grade concentrate, it’s almost a non-starter. Everything downstream is expensive, so you have to minimise the mass you’re treating.”

The operating margins are thin. Some REEs - notably neodymium, praseodymium, terbium and dysprosium for permanent magnets - drive most of the value. Others are neutral, niche, or even liabilities that must be stockpiled or given away. That makes project economics precarious, highly sensitive to both prices and recoveries.

Bespoke technology, not just metallurgy

Perhaps the biggest message Damien left the audience with is that rare earth projects aren’t just mining projects. They’re technology development programs.

“When we worked on the Kvanefjeld project in Greenland, there was no precedent for the dominant mineral there, steenstrupine. We had to start with a blank sheet of paper and invent a new flow sheet. That’s the reality for many rare earth deposits - you can’t just copy and paste from somewhere else.”

That means R&D, collaboration with universities, and often a willingness to embrace unproven methods. Governments are funnelling money into this space for strategic reasons, and Damien believes breakthroughs will come. But for now, solvent extraction remains king, and the “art” of separation is guarded know-how built up through experience.

Conclusion: enough to be dangerous

Damien closed with a wry warning for geologists and engineers outside metallurgy: “You now know enough to be dangerous. Beware Dr Google - you’ll disappear down rabbit holes and come out with the wrong answers. The traps for young players are everywhere.”

His final caution was clear: most REE deposits are low grade, metallurgically complex, and not currently economic. A rare earth geological anomaly does not equal a rare earth project.

Yet the demand is real and growing. Permanent magnets for electric vehicles and wind turbines, high-performance phosphors, catalysts, and advanced alloys all rely on this small group of elements. The world needs them - and as Damien made plain, producing them is anything but simple.

Biography

Damien Krebs is a metallurgical engineer with a masters in mineral economics with significant experience in the development of processes for treating rare earth ores. With over 15 years in rare earths and prior extensive experience in complex hydrometallurgy he is well suited to the challenges of rare earth extractive metallurgy. He has worked for over a decade in technology development for nickel and cobalt metallurgy with BHP which includes both laterite and sulphide ores.

While working across multiple jurisdictions in project development he made many mistakes in the metallurgically complex fields including; pressure leaching, rare earths, uranium, lithium and phosphate. These learnings provided extensive experience in the development of metallurgical processes and thus holds a number of international patents and patent applications for nickel. lithium and rare earth processing. Current work includes leading the development of Primero proprietary lithium refining technology and rare earth consulting. He has a wide range of contacts through the global mining industry for which he has served for over 25 years professionally.