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EXTRACTING RARE EARTHS FROM WASTE
RARE EARTH ELEMENTS present an environmental paradox: REEs are key to green technologies such as solar panels, wind turbines, and electric vehicles. Yet their rarity involves mining that causes significant environmental damage, not to say political quandaries. What’s more, REEs are often found mixed with radioactive elements, and extracting them creates low-level nuclear waste. This paradox and a promising resolution are described by Sam Kean in “An Electronic Jolt Strips Valuable Metals From Waste,” AAAS Science, February 11, 2022.
Chemist James Tour and other researchers at Rice University devised this process of efficient extraction. These pulses of heat, Kean writes, “make it easier to extract REEs from industrial waste. The technique is roughly twice as efficient as current methods and uses far more benign chemicals.”
Retrieving REEs from Coal Fly Ash. Kean describes, “Tour’s team tested its process on fly ash, a powdery gray byproduct of burning coal that contains concentrated levels of the REEs originally present in the coal. The researchers mixed the ash with carbon black to improve electrical conductivity, and then placed the mixture in clear quartz tubes 1 to 2 centimeters wide and 5 to 8 centimeters long. Capacitors on the ends of the tubes sent a pulse of current through, causing the tube to flash yellow-white and produce a tiny puff of smoke. The temperature of the mixed powders spiked to 3000°C within 1 second, then rapidly cooled.”
Shocking REEs Loose. Kean continues, “That spike of heat does two things. When coal is burned as fuel, microscopic bits of glass form inside and trap REEs, making them hard to extract. But the bursts of electric heat shock and shatter the glass, freeing the rare earths. Flash heating also induces chemical changes: Phosphates of REEs transform into REE oxides, which are more soluble and easily extractable.”
A Less Corrosive Process. “As a result of these changes,” Kean notes, “Tour’s group can use less corrosive solutions to extract the REEs. Tour’s team gets by with concentrations of hydrochloric acid 120 times lower than current extraction methods, and still manages to extract twice as much.”
Red Mud and Old Laptops. There are other feedstocks beyond fly ash for extracting these REEs. Tour’s team has experimented with red mud, a byproduct of aluminum production. They’ve also extracted REEs from the circuit board of a discarded laptop.
Mitigating Economic and Political Quandaries. Cost-efficient extraction of REEs could rewrite economic and political realities. As noted here at SimanaitisSays back in July 17, 2016, “Rare earths are neither earths (chemically, they’re metals), nor are they particularly rare…. However, the rare earths tend to be found in ores peculiarly situated around the world.”
Indeed, as noted in Kean’s article, “Other countries have complained that China uses its market dominance to drive up prices by limiting exports.
Scaling Up Still To Come. Thus far, the technology developed by Tour and his team is laboratory-based. “As for scaling up, the team previously developed a flash heating process to transform old tires and plastics into graphene, and a spinoff company has already scaled that process up using larger flash heaters.”
No Lack of Feedstock. Kean concludes, “If Tour’s method does work out, there’s plenty of industrial waste to have at. Every year, humankind produces 40 million tons of electronic waste, 150 million tons of red mud, and 750 million tons of coal fly ash, much of it piled in giant mounds. Considering that burning coal helped create our current environmental mess, it would be fitting if the spark for green technologies could be extracted from its waste.” ds
© Dennis Simanaitis, SimanaitisSays.com, 2022
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