Extraction of rare earths from fertilizer byproducts may soon be a reality

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“Today, an estimated 200,000 tonnes of rare earth elements are trapped in untreated phosphogypsum waste in Florida alone,” said Lauren Greenlee, who is leading the Penn State effort with co-investigator Rui Shi, in a press release.

Greenlee explained that the phosphogypsum is channeled to ditches and ponds for indefinite storage.

“This source of rare earth elements is currently untapped due to the challenges associated with radioactive species and the difficulty of separating individual elements,” she said. “The vision of this project is to discover new mechanisms, materials and separation processes to recover valuable resources, including rare earth elements, fertilizers and clean water, from the waste streams of the fertilizer industry, paving the way for a sustainable domestic supply of rare earths. elements and a sustainable agricultural sector.

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. “

The Case Western Reserve team is responsible for developing the molecules to lock onto specific rare earth elements. Their design will be guided by the computer modeling work carried out at Clemson. Once the peptides are developed, Greenlee will study how they work in aqueous solutions, while Shi will use systems analysis tools, including techno-economic analysis and life cycle assessment, to assess environmental impacts and economic feasibility. of the proposed rare earth element recovery. system under various design and operating conditions.

“We want to move away from current environmental impacts to be more sustainable, and we can do that by translating basic research and lab results into environmental and economic impacts at the systems level,” said Shi. “Then we can feed the sustainability results back into the design to guide future research goals while advancing rare earth element recovery and phosphogypsum processing. “

Shi pointed out that the proposed project will complement other research from Penn State that focuses on using natural protein molecules to extract pooled rare earth elements 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. Greenlee explained, noting that his team will examine interactions at the atomic level using X-ray absorption spectroscopy to validate how molecules exchange atoms when they bind.

“With modeling and experimentation, we’ll continue to iterate to make sure we understand how molecules work together. “


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