Sustainable extraction of rare earth elements from fertilizer by-products


Penn State engineers received a grant from the National Science Foundation to recover rare earth elements from phosphogypsum, a fertilizer byproduct stored indefinitely in open dumps and pumped into designated lakes, pictured here .

Despite their name, rare earth elements are not that rare. The 17 metallic elements are ubiquitous in nature and are becoming even more common in technology, as an essential component of microchips and more. The “rare” description relates to the difficulty of extracting them in a usable form. The normal technique for extracting them from composite minerals is generally energy intensive and produces significant carbon emissions, and much of the rare earth elements are lost in the wastes of other industrial processes.

To develop a more sustainable process that can extract rare earth elements from phosphogypsum, a byproduct of fertilizer production, researchers at Penn State received a National Science Foundation grant of $ 571,658 over four years in as part of a collaboration with Case Western Reserve University and Clemson University totaling $ 1.7 million in funding. Each university is independently funded to pursue a specific aspect of the project, but the project is centrally coordinated by researchers from Case Western Reserve. Lauren Greenlee, associate professor of chemical engineering, is leading the Penn State effort with co-principal investigator Rui Shi, assistant professor of chemical engineering.

“Today, an estimated 200,000 tonnes of rare earth elements are trapped in untreated phosphogypsum waste in Florida alone,” said Greenlee, explaining that the phosphogypsum is being routed to ditches and ponds for storage. indefinite. “This source of rare earth elements is currently untapped due to the challenges associated with radioactive species and the difficulty of separating individual elements. The vision of this project is to discover new separation mechanisms, materials and processes to recover valuable resources, including rare earth elements, fertilizers and clean water, from industrial waste streams. fertilizers, paving the way for a sustainable domestic supply of rare earth elements. and a sustainable agricultural sector.

Greenlee also noted that the United States largely depends on international sources for the supply of rare earth elements, and the COVID-19[female[feminine The pandemic has caused long delays in supply chains.

“This is a significant problem that is compounded by the economic, environmental and safety complexities of obtaining and using rare earth elements internationally,” said Greenlee.

Phosphogypsum is formed when phosphate rock is transformed into fertilizer and contains small amounts of naturally occurring radioactive elements, such as uranium and thorium. Due to this radioactivity, the by-product is stored indefinitely and improper storage can contaminate soil, water and the atmosphere. To harvest rare earth elements trapped in phosphogypsum, researchers propose a multi-step process using modified peptides capable of accurately identifying and separating rare earth elements across a specialized membrane.

“The individual rare earth elements have similar sizes and identical formal charges, so traditional membrane separation mechanisms are insufficient,” Greenlee said. “A key technical objective of this research is to discover the mechanisms underlying the selectivity of peptide ions and to take advantage of these mechanisms to design a new class of highly selective membranes. “

Case Western Reserve researchers Christine Duval, Principal Investigator and Assistant Professor of Chemical Engineering, and Julie Renner, Co-Principal Investigator and Assistant Professor of Chemical and Biomolecular Engineering, will develop molecules to cling to specific rare earth elements . Their design will be guided by the computer modeling work of Rachel Getman, Principal Investigator and Associate Professor of Chemical and Biomolecular Engineering at Clemson. Once the peptides are developed, Greenlee will study how they function in aqueous solutions, while Shi will use systems analysis tools, including techno-economic analysis and life cycle assessment, to assess environmental impacts and the economic feasibility of the proposed recovery of rare earth elements. system under various design and operating conditions.

“What are the overall sustainability implications of this process? Shi asked. “We want to move away from current environmental impacts to be more sustainable, and we can do this by translating basic and lab-scale results into environmental and economic impacts at the systems level. Then we can feed the sustainability results back into the design to guide future research targets while advancing rare earth element recovery and phosphogypsum processing. “

The proposed project will also complement other research from the State of Pennsylvania, including work using natural protein molecules to extract rare earth elements pooled from other sources of industrial waste.

“For our project, the hypothesis is that the water molecules associated with peptides binding to rare earth elements reorganize, and we can precisely control this reorganization to be more efficient depending on the individual rare earth element. “said Greenlee, noting that his team will examine interactions at the atomic level using X-ray absorption spectroscopy to validate how molecules exchange atoms when they bond. “With modeling and experimentation, we’ll continue to iterate to make sure we understand how molecules work together. ”

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