President Biden signed an executive order (EO 14017) in February 2021 to review U.S. supply chains’ reliance on foreign suppliers to set the U.S. on the path of rare earth elements (REEs) independence. REEs have become essential components to healthcare, clean energy, and communication technologies like electric vehicles, wind turbines, microchips, and batteries due to their unique physical and chemical properties. The process of mining REEs from natural deposits is costly and harmful to the environment. Luckily, scientific advances in the field of agromining are offering a more sustainable alternative.
What are REEs?
REEs are known as ‘rare’ not because they are exceptionally uncommon, but because they are not found in pure form and require several extracting steps. Across the globe, there is a growing demand for advancing technologies made from REEs like consumer electronics (mobile phones and tablets), which is predicted to reach $2.5 trillion by 2030. In 2020, U.S. imported over 80% of REEs from China due to the lack of domestic capability for REEs production from finite ore sources, or extraction from municipal landfills like electronic wastes (e-wastes). Recent published studies confirm REEs extraction from urban wastes can be a promising alternative to replenish REEs required to meet future technological needs, mitigate environmental impacts, and subsequently address national priorities like President Biden’s order to “identifying risks in the supply chain for critical minerals and other identified strategic materials, including rare earth elements (as determined by the Secretary of Defense), and policy recommendations to address these risks.”
REEs extraction from e-wastes is beginning to gain momentum in the U.S. that can address national supply chain risks. Recent studies show that only 25% of 1.8 million tons of domestic e-waste were recycled or reused in 2018. According to the UN Environment Programme, over 53 million tons of e-waste were generated in 2019, with approximately $57 billion raw materials containing precious REEs and metals (platinum, gold, and silver). Despite the many scientific developments made so far, most REE extraction technologies exist on a very small scale, which is why several countries export their e-waste to other countries like China for extraction.
Japan used to be heavily dependent on China’s REE export, but in 2010, Japan swiftly turned to its municipal landfills and e-wastes for addressing their critical minerals and materials like REEs. Japanese National Institute for Materials Science reported that their urban wastes held over 290,000 tons of REEs, which encouraged mining companies (like Dowa Holdings in Kosaka, Japan) to build recycling facilities and extract valuable rare materials from old electronics. So far, the recycling practices successfully recover REEs and metals from semiconductors and display units.
What are common REE recycling techniques?
Two highly applied and mature REE extraction techniques are leaching and solvent extraction. Leaching is a simple process, requiring low energy and providing high selectivity of REEs. However, it needs a high quantity of chemical reagents that can generate hazardous byproducts, and it is not efficient when applied to low REE concentrations. On the other hand, solvent extraction is an effective separation technique that is commercially used and produces high purity single REE solution or mixed REE compounds, but it does struggle from inefficiencies, being time-consuming and labor-intensive. Other extraction approaches are immature and growing techniques like photochemistry, ultrasonic leaching, and electrochemical separation. Biological and agronomical approaches like agromining and bio-leaching are emerging technologies that allow for environmentally friendly REE extraction from e-wastes.
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How Agromining works
Encouraging e-waste recycling could be achieved with new and sustainable techniques. Agromining can be a sustainable solution for old household electronics (mobile phones, laptops, and TVs) with high REE concentration. The agromining processes employ plant species with high hyperaccumulation attributes like fast-growing on REE-rich soils and accumulating a high amount of REEs. After REEs have been concentrated in the body of a plant or multi-cellular fungi like mushrooms, REE extraction into individual elements can be achieved through several hydrometallurgical or pyrometallurgical processes. Utilization of the hyperaccumulating characteristics of plants for agromining makes it an environmentally friendly and low-cost approach. But, it requires a lot of land and constant plant care.
REEs supply from recycling e-wastes via agromining can be a good policy recommendation for President Biden’s executive order on U.S. supply chains of critical materials. Agromining can address several national priorities like enhancing domestic job creation and manufacturing capacity, as well as mitigating supply chain risks and environmental impacts. Besides, agromining can help small to medium-sized companies and municipal landfills in the U.S. and developing countries to participate in REE extraction at a fraction of REEs mining from finite ore sources.