Rare earth recycling: Is it worth it?

Rare earth metals are absolutely critical to modern life. Fiber optic communications require erbium. Neodymium is a critical component in modern permanent magnets. Without a steady supply of rare earth metals, we would find ourselves in some difficulty, and things may get even more critical in the future—quantum memory may lie in the hands of praseodymium.

Despite this need for rare earth metals, pretty much the entire supply comes from one country: China. In 2010, politicians finally noticed this, as China started restricting its export. In response, a team of researchers from the Netherlands and the United Kingdom have been investigating our ability to recycle rare earth metals.

China's open-pit mines

In an apparent response to environmental pressure, China began to restrict the exportation of rare earth metals in 2010. At the time, China controlled 95 percent of the market. Manufacturers were rocked by the price fluctuations, eventually complaining to the World Trade Organization in an effort to stabilize supply. Even if you're suspicious of China's true motives, mining rare earths is a dirty job, involving some pretty vicious acids, bases, solvents—and the whole process raises the risk of miners breathing in a serious amount of radioactive dust. So whatever China's underlying motive was, cleaning up the mining industry is a good thing.

At the time, rare earth mining and refining was performed by companies ranging in size from tiny backyard operations, right up to very large companies. The technologies used also spanned the range from primitive and inefficient to the modern and efficient. ("Efficient" is a relative term here; I mean more efficient than the low-technology scenarios.) But the plain fact is that mining rare earths (and mining in general) is a messy and damaging process. Not just in local damage to the environment—poor labor conditions can make for a shortened life expectancy.

So even if new mines were opened (or old ones were re-opened), the lower concentration of rare earths in the ore would make it difficult to operate in a clean manner and to compete with Chinese mining operations.

But quantifying those difficulties is not simple. To evaluate the environmental impact of a magnet's production, the researchers turned to the literature to figure out things like the contents of the ore, the strength and volume of solvents used, the amount of acid used, the amount of energy used, and (since the ore has radioactive products in it) the expected radiation dose that workers would be exposed to. Since every mine, refinery, and magnet manufacturer uses a slightly different process, the researchers broke their data up into a high-technology version of the process, a low-technology version, and a middle-of-the-road process. These represent low, high, and medium environmental impacts.

For the mining operations, the main difference between high-technology and low-technology scenarios is human exposure to toxic elements. Although the main hazard is hydrogen fluoride, to provide a consistent measure of toxicity, the researchers expressed the total exposure as an equivalent dose of 1,4-dichlorobenzene. Under their units, one kilogram of neodymium oxide results in an exposure of between 36 and 320kg of 1,4-dichlorobenzene. To put this figure in perspective, the amount of 1,4-dichlorobenzene allowed in water is 75 micrograms per liter, and the LD50 (the dose that will kill half the specimens in a study) in rats is 500mg/kg. Extrapolating this to humans—always a risky business—we can say that about 40g will kill a person.

All of this means that even the clean process is quite dirty, while the dirty process has the potential to be quite hazardous.

Making the magnets and their protective coatings is also rather messy, but it's generally less so than the mining. Even if the neodymium were to be recycled, the initial costs of mining and the recurring cost of forming it into magnets stay with the magnet—but if the neodymium can be recycled many times, the mining contribution becomes small compared to the magnet manufacturing.

Is recycling any better?

In response to price fluctuations, the idea of recycling neodymium has been gaining currency. But although recycling sounds good in principle, it's often an energy-intensive process that may cause more problems than it solves. To find out whether it does, the team compared the figures above to the environmental impact associated with recycling the neodymium in the magnets of hard drives. Why hard drives? The article only says that they are convenient to access, but I suspect a second reason is that they are one of the few neodymium-reliant products that has a short life cycle, making recycling a more viable option.

In this study, the researchers investigated two recycling methods. One involved collecting hard drives from a conveyor belt of scrap electronics. The hard drives were then manually disassembled, and the magnets were deposited into a container with hydrogen gas. The neodymium absorbed the hydrogen gas, causing the magnets to disintegrate into a powder. The powder was then sieved to remove the fragments from the magnets' coating and then milled to break up the remaining larger particles. After that, the powder was equivalent to where mined material is when it's midway through making the magnet—a remarkably simple process.

As a result, the recycled magnets have much less environmental impact. In other words, when we make a magnet from the recycled product, we use less energy and emit fewer pollutants than when we make a magnet from the refined neodymium oxide delivered from the mine. That seems pretty promising, but there is still the issue that the magnets are removed by hand.

The alternative to hand-picking the magnets was to drop the entire hard drive into a shredder, resulting in a huge mess from which the neodymium must be leached using sulfuric acid. Here things get confusing. In the experimental section, the researchers claim that 99 percent of the neodymium can be reclaimed using this method, while in the discussion, it's claimed that more than 90 percent of the neodymium is lost during shredding. I suspect that the leaching process extracts 99 percent of the neodymium that is made available to it by a very inefficient shredding process. That is, the acid never comes in contact with 90 percent of the neodymium.

In terms of environmental impact, both recycling methods reduce the burden by about an order of magnitude compared to mining (though shredding is worse than disassembly). Even then, the process is still rather dirty, but the human toxicity element is reduced by about an order or magnitude compared to the original magnet production. The disassembly method, in contrast, results in practically all the neodymium being recovered. It looks good environmentally, and that's even with the environmental assessment ignoring the scarcity of the rare earth elements.

So what do we learn from this? It is a little hard to say, as the conclusions are a bit mixed. First, an automated recycling process (such as the shredder method) is likely to be uneconomical due to the high neodymium losses, while a method that involves disassembly will only be economic if wages are low. On the surface, then, recycling doesn't look like an automatic win.

And if we consider the overall picture, either option could be dwarfed by reducing the environmental impact of the mining process. China's uneven enforcement of its own (not very strong) environmental laws is probably the biggest barrier. Furthermore, it's likely that with some additional effort, mining operations can be made even cleaner than the high-technology scenario discussed by the researchers. Without research like this, though, we wouldn't even know where to start.