21ST CENTURY ALCHEMY
Turning waste into gold
IMAGE:
THE GOLD NUGGET OBTAINED FROM COMPUTER MOTHERBOARDS IN THREE PARTS. THE LARGEST OF THESE PARTS IS AROUND FIVE MILLIMETRES WIDE.
view moreCREDIT: (PHOTOGRAPH: ETH ZURICH / ALAN KOVACEVIC)
Transforming base materials into gold was one of the elusive goals of the alchemists of yore. Now Professor Raffaele Mezzenga from the Department of Health Sciences and Technology at ETH Zurich has accomplished something in that vein. He has not of course transformed another chemical element into gold, as the alchemists sought to do. But he has managed to recover gold from electronic waste using a byproduct of the cheesemaking process.
Electronic waste contains a variety of valuable metals, including copper, cobalt, and even significant amounts of gold. Recovering this gold from disused smartphones and computers is an attractive proposition in view of the rising demand for the precious metal. However, the recovery methods devised to date are energy-intensive and often require the use of highly toxic chemicals. Now, a group led by ETH Professor Mezzenga has come up with a very efficient, cost-effective, and above all far more sustainable method: with a sponge made from a protein matrix, the researchers have successfully extracted gold from electronic waste.
Selective gold adsorption
To manufacture the sponge, Mohammad Peydayesh, a senior scientist in Mezzenga’s Group, and his colleagues denatured whey proteins under acidic conditions and high temperatures, so that they aggregated into protein nanofibrils in a gel. The scientists then dried the gel, creating a sponge out of these protein fibrils.
To recover gold in the laboratory experiment, the team salvaged the electronic motherboards from 20 old computer motherboards and extracted the metal parts. They dissolved these parts in an acid bath so as to ionise the metals.
When they placed the protein fibre sponge in the metal ion solution, the gold ions adhered to the protein fibres. Other metal ions can also adhere to the fibres, but gold ions do so much more efficiently. The researchers demonstrated this in their paper, which they have published in the journal Advanced Materials.
As the next step, the researchers heated the sponge. This reduced the gold ions into flakes, which the scientists subsequently melted down into a gold nugget. In this way, they obtained a nugget of around 450 milligrams out of the 20 computer motherboards. The nugget was 91 percent gold (the remainder being copper), which corresponds to 22 carats.
Economically viable
The new technology is commercially viable, as Mezzenga’s calculations show: procurement costs for the source materials added to the energy costs for the entire process are 50 times lower than the value of the gold that can be recovered.
Next, the researchers want to develop the technology to ready it for the market. Although electronic waste is the most promising starting product from which they want to extract gold, there are other possible sources. These include industrial waste from microchip manufacturing or from gold-plating processes. In addition, the scientists plan to investigate whether they can manufacture the protein fibril sponges out of other protein-rich byproducts or waste products from the food industry.
“The fact I love the most is that we’re using a food industry byproduct to obtain gold from electronic waste,” Mezzenga says. In a very real sense, he observes, the method transforms two waste products into gold. “You can’t get much more sustainable than that!”
JOURNAL
Advanced Materials
ARTICLE TITLE
Gold Recovery from E-Waste by Food-Waste Amyloid Aerogels
A bright idea for recycling rare-earth phosphors from used fluorescent bulbs
Recycling facilities collect glass and mercury from thrown away fluorescent bulbs, but discarded lighting could also supply rare-earth metals for reuse. The 17 metals referred to as rare earths aren’t all widely available and aren’t easily extracted with existing recycling methods. Now, researchers have found a simpler way to collect slightly magnetic particles that contain rare-earth metals from spent fluorescent bulbs. The team describes its proof-of-concept magnetized chromatography method in ACS Sustainable Chemistry & Engineering.
Many modern technologies, such as electric vehicles and microchips, use rare earths because of their unique magnetic, electrical and optical characteristics. However, only a handful of countries have untapped deposits of these metals. Large-scale rare-earth recycling from outdated, broken devices is challenging because the metals are integrated into different components and are present only in small amounts. In discarded fluorescent lighting, mixtures of rare-earth-based phosphors, the substances that contribute to a light’s color, are found in a thin coating inside the bulb. So, Laura Kuger, Matthias Franzreb and colleagues wanted to develop a low-tech method to easily collect these phosphors by taking advantage of the elements’ weak magnetic properties.
The researchers used a wire coil to externally apply a magnetic field to a glass chromatography column filled with stacked disks of stainless-steel mesh. They then prepared a demonstration sample to pass through the column to see if it could capture the phosphors. First, the researchers obtained three different weakly magnetic rare-earth phosphors from a lamp manufacturer. Next, the team mimicked old fluorescent lamp parts by mixing the phosphor particles in a liquid solution with nonmagnetic silica oxide and strongly magnetic iron oxide nanoparticles, representing glass and metal components in the bulbs, respectively. Then, when the liquid was injected and flowed through the chromatography column, the phosphors and iron oxide nanoparticles stuck to the magnetized stainless-steel mesh, while the water and silica particles flowed out the other end.
To remove the phosphors from the column, the researchers slowly reduced the strength of the external magnetic field while rinsing the column with liquid. Finally, the strongly magnetic iron oxide nanoparticles were released from the column when the magnetic field was turned off. The researchers observed that their method recovered 93% of the rare-earth phosphors from the initial mixture that mimicked lamp components. While more work is needed to separate individual rare-earth elements from the phosphors and to scale the method for industrial recycling applications, Kuger, Franzreb and colleagues say their approach is a step toward a practical way to turn old light bulbs into new technologies for a brighter and more sustainable future.
The authors acknowledge funding from the German Research Foundation.
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JOURNAL
ACS Sustainable Chemistry & Engineering
ARTICLE TITLE
“Design of a Magnetic Field-Controlled Chromatography Process for Efficient and Selective Fractionation of Rare Earth Phosphors from End-of-Life Fluorescent Lamps”
Mining the treasures locked away in produced water
Reports and ProceedingsIMAGE:
THE WATER RECOVERED FROM HYDROCARBON RESERVOIRS CONTAINS CRITICAL MINERALS THAT ARE KEY TO MANY TECHNICAL AND INDUSTRIAL OPERATIONS.
view moreCREDIT: TEXAS A&M ENGINEERING
In an ironic twist, a treasure trove of critical minerals is dumped out with water considered too polluted and expensive to clean.
Texas A&M University researcher Dr. Hamidreza Samouei is investigating the components of produced water and says this waste byproduct of oil and gas operations contains nearly every element in the periodic table, including those of significant interest to national economies.
His goal is to treat the water using unwanted carbon dioxide (CO2) in stages to recover these valuable elements and ultimately produce fresh water for agricultural use once the processes are complete.
“Recognizing the latent value within produced water can offer tangible solutions to some of the world’s most pressing environmental challenges, from CO2 emissions to the increasing scarcity of certain minerals and water itself,” said Samouei, a research assistant professor in the Harold Vance Department of Petroleum Engineering.
Samouei’s “brine mining” research was featured in a January 2024 article in the Society of Petroleum Engineers’ Journal of Petroleum Technology titled “Liquid Goldmine: unlocking the Critical Mineral Potential of Produced Water using Carbon Dioxide.” He introduced the topic at the Middle East Water Week Conference and Exhibition held December 2023 in Saudi Arabia and will report his most recent discoveries at the Annual Produced Water Society Conference on February 2024 in Houston, Texas.
Why is produced water thrown away?
Water accumulates in subsurface areas where geological functions happen, like hydrocarbon reservoirs, and it dissolves and stores vast quantities of minerals and other elements. During oil and gas operations, an average of six 42-gallon barrels of this “produced” water are recovered for every one barrel of oil, and in rare cases, up to a staggering ratio of 500 to 1. It is up to 10 times saltier than seawater and contains about 6,000 times more minerals.
In 2020, the annual global quantity of produced water recovered from oil and gas operations surpassed 240 billion barrels, with Texas alone recovering 33 million barrels daily. The oilfields of the Permian Basin in Texas generate more produced water than all other U.S. shale plays combined. Treating this vast volume is cost-prohibitive, so produced water is mainly considered a waste product and injected in subsurface disposal fields for safe containment.
The hidden values in brine
Since everything in produced water has never been cataloged, Samouei’s research began with the basics. He collected produced water samples around the U.S. and created a standardized method of analyzing the water’s content. That’s when he learned it contained nearly everything listed in the periodic table of elements.
Samouei’s findings included critical minerals like lithium, rubidium, cesium, gallium and platinum group metals – substances fundamental to the current and future technologies advancing computer, energy and transportation industries. More importantly, like other brines, produced water featured less expensive but abundant quantities of sodium, potassium, magnesium and calcium – used in manufacturing processes, fertilizer production and other industries.
All these minerals can be far more lucrative than the oil that comes up with produced water, so water reclamation costs could be easily offset by selling the recovered minerals.
A better treatment
Samouei explained that while desalinating produced water has been considered, the approach of first mining all the salt and minerals before treating the water had not been explored.
Much of his current research centers on developing the best flow of methods for extracting valuable minerals from brine in stages of refinement using CO2 desalination, which he says is “a groundbreaking approach to targeted mineral recovery from produced water.” The process includes a variety of filtration techniques, such as ultrafiltration and nanofiltration, and even utilizes reverse osmosis.
Commercialization potential
The research is creating a baseline for brine mining, whether using produced water or other brackish sources, but Samouei said further development would need a funding source. Government sponsors are concentrating on critical mineral mining in places such as the sea floor or even asteroids, not on something as close to home as produced water.
Samouei said he hopes to change the oil and gas industry's view of produced water, first to see it as a lucrative means of receiving money and later, perhaps in 10 years, as a source for their own mining operations.
“Produced water may not be beautiful if we look at it as a waste,” he said, “but it will be impactful to the world’s next generations if we look at it as a resource.”
Once produced water is separated from oil, the intended process involves a brine mining process to recover critical minerals and other elements before the water is cleaned for specific agriculture operations or for use in fracturing operations to recover more oil.
CREDIT
Texas A&M Engineering
JOURNAL
Journal of Petroleum Technology
ARTICLE TITLE
Liquid Goldmine: Unlocking the Critical Mineral Potential of Produced Water Using Carbon Dioxide
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