Inefficient, expensive, and environmentally hazardous technologies hamper recycling electronic waste. Recycling rare earth metals in particular has been difficult. It takes several of them to make a single device but not enough to make recycling them economically viable. Recent years, however, have seen research on new methods.
Rare earth elements comprise 17 metals that all look and behave pretty much alike. They had little practical use until the electronics industry came to depend on them. In electronics, in fact, each one has unique electrical properties that makes it suitable for niche uses where nothing else works. Electronic gadgets go obsolete so quickly that electronic waste has become a huge problem.
In addition, electric vehicles, solar panels, and wind turbines all require rare earth minerals. A shortage of these metals will limit the chance of meeting emission reduction targets. Recycling rare earth metals is therefore a critical requirement for addressing climate change.
Rare earth elements are actually plentiful in the earth’s crust. They just never occur in their own ore. “Rare” refers to the sparseness of economically viable ore deposits.
Mining rare earth metals comes at a high economic, environmental, and geopolitical cost. The environmental impact comes from the strong acids needed to separate them from their surroundings. Ironically, some of them are essential for clean energy technologies. Geopolitically, China controls about 90% of rare earth production. When it has cut exports, the rest of the world suffers.
Recycling rare earth elements suffers from the same conditions that make mining them so difficult. They are present in all kinds of consumer electronics, but only in tiny quantities. It has not seemed economically worthwhile to try to extract them from obsolete electronics. No more than 5% of rare earth metals ever get recycled.
Recycling rare earth metals with bacteria
The Idaho National Laboratory has for the past several years explored acids produced by the bacterium Gluconobacter oxydans, which is very common. It is present in rotting fruit, for example.
The laboratory at first used it for recycling rare earth metals from the spent catalyst left over from petroleum refineries.
The bacterium produces gluconic acid among others. The acids dissolve rare earth elements from surrounding materials in a process called bioleaching. When precipitated from the acid, they can be purified for industrial use.
Large amounts of rare earth elements also occur in certain mining wastes. Phosphoric rock, for example, provides phosphoric acid, which is used to make fertilizer and other products. In the process, large amounts of rare earth elements exist in a waste product called phosphogypsum (PG). More than a billion tons of PG are piled up in storage facilities nationwide.
Every year, some 100,000 tons of rare earths end up in PG waste worldwide. In comparison, the world mines 126,000 tons of rare-earth oxides.
But the bioleaching technique also works well with small amounts of rare earth metals. It is very economical. In fact, the chief expense is the glucose needed to feed the Gluconobacter oxydans. Purchasing it from a commercial source accounted for 44% of the cost. So the laboratory experimented with cheaper ways to get glucose and found how to extract it from potato pulp, corn stover, and other agricultural wastes.
This process presents some of the same difficulties as making ethanol from cellulose. The team needs to solve these and other problems before industry can use bioleaching.
Recycling rare earth metals with flash Joule heating
Researchers at Rice University developed a technique called flash joule heating to produce graphene from organic wastes (including plastic waste and food waste).
More recently, they have used it to extract heavy metals from various wastes. For example, they can grind up old circuit boards and subject them to a jolt of electricity that heats the waste to about 5,600 degrees Fahrenheit. It vaporizes everything and, in the process, separates it into basic elements.
After the flash, the separated components are dissolved in a diluted hydrochloric acid. It is much less toxic than the strong nitric acid used in mining rare earth metals.
The Rice team can separate elements from the resulting gases for either reuse or disposal. This technique recovers rare earth elements along with all the other metals in the wastes. These include gold, cobalt, and others that bring a high price on the market. The non-metallic components are safe to bury in soil.
The whole process uses about 939 kWh for every ton of materials it processes. Commercial smelting furnaces use 80 times that much electricity.
The process works very well in the lab. Scaling it up for commercial use will require much more research.
Recycling rare earth metals with membrane extraction
I have mentioned that electronic gadgets contain only a small proportion of rare earth elements. But they include magnets that are about 30-33% rare earths. In other words, using membrane extraction to recover a ton of rare earth elements from recycled electronic waste requires only three tons of magnets. That is a much higher density than any mining operation.
Data-security concerns result in 35% of used hard drives being shredded. Recycling them could result in a thousand metric tons of recovered rare earth metals.
In addition, the motor in a hybrid car uses about two pounds of neodymium, one the rare earth elements. A 3.5-megawatt wind turbine requires more than half a ton of various rare earth metals.
Oak Ridge National Laboratory has developed a membrane extraction system to separate rare earth metals from the kinds of magnets used in computer hard drives, electric vehicles, or wind turbines. It dissolves the magnets in nitric acid and feeds the solution through polymer membranes. The membranes allow only rare earth metals to pass through.
The magnets are about 70% iron, but the material that passes through the membranes is about 99.5% pure rare earth oxides.
Unlike the previous two processes described in this article, the membrane extraction technique has been licensed to a company, Dallas-based Momentum Technologies, to scale up the process. It can already to produce commercial-scale batches of recycled rare earth metals.
Recycling rare earth metals with borate flux
Nissan started working on a new process to recycle rare earth metals from electric motors in 2017. It involves melting a used motor at a temperature of about 2,500 degrees Fahrenheit, adding an oxide of iron to oxidize the rare earth metals, and then a borate-based flux. The borate separates the molten mixture into two layers. The lighter top layer contains the rare earths. It can be skimmed off easily.
The company claims its new recycling process can recover 98% of the rare earth elements in a motor. It also takes half the time of the manual processes it currently uses. Nissan hopes to have it ready to implement by the middle of the current decade.
Critical materials: researchers eye huge supply of rare-earth elements from mining waste / Idaho National Laboratory. March 13, 2019
Flash Joule process recovers precious metals from e-waste / The Engineer. October 5, 2021
From trash to treasure: Electronic waste is mined for rare earth elements / Oak Ridge National Laboratory. August 14, 2019
Inside the high-powered process that could recycle rare earth metals / Rahul Rao, Popular Science. February 11, 2022
Metal-eating microbes prove cost-effective for recycling rare earth elements / Cory Hatch, Idaho National Laboratory. March 5, 2018
Nissan is testing a more efficient way to recycle rare-earth metals from EV motors / I. Bonifacic, Engadget. September 3, 2021
Rare opportunity to recycle rare earths / Curt Harler, Recycling Today. January 3, 2018