Rare earth elements (REE) are a group of elements containing the 15 elements of the lanthanide series on the periodic table along with scandium and yttrium. Collectively, they have similar physical and chemical properties (Cheisson, 2019), and while REEs are found throughout the earth’s crust they occur in low concentrations and often as a mixture of elements (Mattocks, 2020; Rumble, 2019). For these reasons REEs are difficult to mine and recycle to high purity (Cheisson, 2019; Mattocks, 2020). REE are used in wide range of defense applications include electronic displays, guidance systems, lasers, and radar and sonar systems and more (Haque, 2014; Jowitt, 2018; Xie, 2014). Over the next 25 years, the projected annual growth rate of certain REEs such as dysprosium is expected to increase up to 14% per year (Alonso, 2012; Dutta, 2016). Due to their importance in technologies that have the potential to transform how they produce, transmit, store, and conserve energy (Abraham, 2015), many REEs are considered energy critical elements by the defense industry. Current technologies to reclaim REEs are operationally inefficient, have high environmental costs (large volumes of highly toxic chemicals) (Jowitt, 2018), and are dominated by Chinese firms and related intellectual property (Xie, 2014). To minimize the reliance on China, the United States is pushing to ‘re-domesticate’ the REEs supply and has stated an explicit goal to utilize urban waste streams and manufacturing waste as a new source of domestic REEs (US DOE, 2011).

The primary objective of this project is to discover a suite of proteins that selectively bind REEs with 100X or higher affinity over metals commonly found in manufacturing and post-consumer e-waste and have >5X selective binding affinity for light rare earth element (LRE) over heavy rare earth element (HRE) and vice versa. The project team anticipates that the next step following the success of the selective REE binding protein identification will be the further engineering and optimization of said proteins for greater affinity for individual HREs or LREs and operational capability under a range of environmental conditions.

This project will conduct an extensive biophysical characterization on proteins that bind the lanthanide metals dysprosium and terbium. The project team will determine the binding affinities and selectivities of 16 REE-binding proteins identified in previous work for the energy-critical REEs: praseodymium, neodymium, europium, terbium, dysprosium, and yttrium (US DOE, 2011). The functional performance of each protein will be evaluated in conditions typical of waste streams and industrial processes. Quantified REE-binding parameters will be compared to the project primary objectives, and the environmental and economic benefits of replacing existing extractants with proteins will be estimated in our Sustainability Analysis.

The low REE separation factors of chelators and extractants is a major reason isolating REEs to high purity is a time and energy intensive process that generates large amounts of waste. The development of highly selective REE-binding molecules would simplify industrial processes and reduce waste by using green technologies from synthetic biology. The project team believes this bio-recycling technology, when fully developed, will serve as means of localizing and building more cost-effective, resilient, and sustainable REE-related supply chains in the United States from metals-rich waste streams.