New environmentally friendly method to extract and separate rare-earth elements

A new method improves the extraction and separation of rare-earth elements—a group of 17 chemical elements critical for technologies such as smart phones and electric car batteries—from unconventional sources. New research led by scientists at Pennsylvania State University and LLNL demonstrates how a protein isolated from bacteria can provide a more environmentally friendly way to extract these metals and to separate them from other metals and from each other. The method could eventually be scaled up to help develop a domestic supply of rare-earth metals from industrial waste and electronics due to be recycled.

Because the U.S. currently imports most of the rare-earth elements it needs, a new focus has been placed on establishing a domestic supply from unconventional sources, including industrial waste from burning coal and mining other metals as well as electronic waste from cell phones and many other materials. These sources are vast but considered “low grade,” because the rare earths are mixed with many other metals and the amount of rare earths present is too low for traditional processes to work well. Furthermore, current methods for extraction and separation rely on harsh chemicals, are labor intensive, sometimes involve hundreds of steps, produce a high volume of waste, and are high cost.

The new method takes advantage of a bacterial protein called lanmodulin, previously discovered by the research team, that is almost a billion times better at binding to rare-earth elements than to other metals. The protein is first immobilized onto tiny beads within a column—a vertical tube commonly used in industrial processes—to which the liquid source material is added. The protein then binds to the rare-earth elements in the sample, which allows only the rare earths to be retained in the column and the remaining liquid drained off. Then, by changing the conditions, for example by changing the acidity or adding additional ingredients, the metals unbind from the protein and can be drained and collected. By carefully changing the conditions in sequence, individual rare-earth elements could be separated.

[Z. Dong, J.A. Mattocks, G.J.-P. Deblonde, D. Hu, Y. Jiao, J.A. Cotruvo Jr., and D.M. Park, Bridging Hydrometallurgy and Biochemistry: A Protein-Based Process for Recovery and Separation of Rare Earth Elements, ACS Central Science (2021), doi: 10.1021/acscentsci.1c00724.]