Penn State University chemical engineers have been awarded a $1.7m grant to develop a sustainable process for recovering rare earth elements from phosphogypsum, a by-product of fertilizer.
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What are Rare Earth Elements and Where are they Found?
Rare earth elements (REEs) comprise 17 metallic elements, made up of 15 lanthanides on the periodic table:
- Lanthanum
- Cerium
- Praseodymium
- Neodymium
- Promethium
- Samarium
- Europium
- Gadolinium
- Terbium
- Dysprosium
- Holmium
- Erbium
- Thulium
- Ytterbium
- Utetium
- Scandium
- Yttrium
Most of them are not as rare as the group name suggests but were named in the 18th and 19th centuries, in comparison to other more common ‘earth’ elements such as lime and magnesia.
Cerium is the most common REE and more abundant than copper or lead.
However, in geological terms, REEs are rarely found in concentrated deposits as coal seams, for example, are making them economically difficult to mine.
They are instead found in four main uncommon rock types; carbonatites, which are unusual igneous rocks derived from carbonate-rich magmas, alkaline igneous settings, ion-absorption clay deposits, and monazite-xenotime-bearer placers deposits.
China Mines 95% of Rare Earth Elements to Satisfy Demand for Hi-Tech Lifestyles and Renewable Energy
Since the late 1990s, China has dominated REE production, utilizing its own ion-absorption clay deposits, known as the ‘South China Clays’.
It is economical for China to do because the clay deposits are simple to extract REEs from using weak acids.
Rare earth elements are used for all sorts of hi-tech equipment, including computers, DVD players, cell phones, lighting, fiber optics, cameras and speakers, and even military equipment, such as jet engines, missile guidance systems, satellites, and anti-missile defense.
An objective of the 2015 Paris Climate Agreement is to limit global warming to below 2 ˚C, preferably 1.5 ˚C, pre-industrial levels. This has increased demand for renewable energy and electric cars, which also require REEs to operate.
In 2010, China announced it would reduce REE exports to fulfill its own rise in demand, but also maintain its dominant position for supplying hi-tech equipment to the rest of the world.
China is also in a strong economic position to control the supply of REEs needed for renewable energies such as solar panels, wind, and tidal power turbines, as well as electric vehicles.
Phosphogypsum Fertilizer Rare Earth Elements Capture Project
Phosphogypsum is a by-product of fertilizer and contains naturally occurring radioactive elements such as uranium and thorium. For this reason, it is stored indefinitely, with associated risks of polluting soil, air, and water.
Therefore, researchers at Penn State University, have devised a multistage approach using engineered peptides, short strings of amino acids that can accurately identify and separate REEs using a specially developed membrane.
As traditional separation methods are insufficient, the project aims to devise new separation techniques, materials, and processes.
The design is led by computational modeling, developed by Rachel Getman, principal investigator and associate professor of chemical and biomolecular engineering at Clemson, with investigators Christine Duval and Julie Renner, developing the molecules that will latch on to specific REEs.
Greenlee will look at how they behave in water and will assess the environmental impact and different economic potentials under variable design and operating situations.
Chemical engineering professor Lauren Greenlee, claims that: “today, an estimated 200,000 tons of rare earth elements are trapped in unprocessed phosphogypsum waste in Florida alone.”
The team identifies that traditional recovery is associated with environmental and economic barriers, whereby they are currently recovered from composite materials, which require the burning of fossil fuels and is labor-intensive
The new project will focus on recovering them in a sustainable way and may be rolled out on a larger scale for environmental and economic benefits.
If the project is successful, it could also reduce the USA’s dependency on China for providing rare earth elements.
National Science Foundation Project Funding
The Penn State REE project is funded by a four-year grant of $571,658, totaling $1.7 million, and is a collaboration with Case Western Reserve University and Clemson University.
Alternative Ways to Recover Rare Earth Elements
RRE recovery is typically carried out using small-scale operations, commonly by leaching and solvent extraction.
Although a simple process, leaching requires a high quantity of hazardous chemical reagents, so is undesirable commercially.
Solvent extraction is an effective technique but is not very efficient because it is labor-intensive and time-consuming.
Another common way for REEs to be recovered is through agromining, also known as e-mining, which involves the transportation of electronic waste, such as old computers, phones, and television from various countries to China for REE extraction.
According to the UN Environment Programme, over 53 million tons of e-waste were generated in 2019, with around $57 billion raw materials containing REEs and metals.
Although often touted as a sustainable method of recycling materials, it is not without its own set of problems that still need to be overcome.
Agromining requires a lot of storage space, recycling plants, landfill waste after REE recovery, and involves transportation costs, which require burning fossil fuels.
The Penn State University Project has the potential to overcome some of the problems associated with traditional REE recovery methods if it can satisfy its own environmental and economic objectives.
References and Further Reading
Sustainable Mining Rare Earth Elements from Fertilizer Byproduct (11.06.2022) Penn State University in SciTechDaily online (accessed 02.11.2022) https://scitechdaily.com/sustainably-mining-rare-earth-elements-from-fertilizer-byproduct/
Explainer: China’s rare earth supplies could be vital bargaining chip in U.S trade war (05.30.2019) Reuters Staff in Reuters online (accessed 02.11.2022) https://www.reuters.com/article/us-usa-china-rareearth-explainer-idUSKCN1T00EK
The Rare Earth Elements – Vital to Modern Technologies and Lifestyles in USGS online (accessed 02.11.2022) https://pubs.usgs.gov/fs/2014/3078/pdf/fs2014-3078.pdf
The Paris Agreement (2015-2016) in UNFCCC online (accessed 02.11.2022) https://unfccc.int/process-and-meetings/the-paris-agreement/the-paris-agreement
A Sustainable Way to Mine Rare Earth Elements from Old Tech Devices: Agromining Explained (05.04.2021) Mirkouei.A in Forbes online (accessed 02.11.2022) https://www.forbes.com/sites/aminmirkouei/2021/05/04/a-sustainable-way-to-mine-rare-earth-elements-from-old-tech-devices-agromining-explained/?sh=769395408121
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