Protein-based approach for high-purity REE separation

D.M. Park, Z. Dong, J. Seidel, P. Diep, C. Madsen J. Cotruvo, Y. Jiao
Lawrence Livermore National Lab,
United States

Keywords: lanmodulin, REE separation, protein-based REE separation, synthetic biology

Summary:

Rare earth element (REEs: Sc, Y, La- Lu) are irreplaceable components in many clean energy and consumer technologies. However, the extraction and subsequent separation of individual REEs from ore-based feedstocks remains a significant economic and environmental challenge. Lanmodulin (LanM), a small, durable bacterial protein that exhibits high affinity and selectivity for REEs, has emerged as a sustainable potential alternative to conventional hydrometallurgical processes. Here, we describe our recent advances in deploying LanMs for recovery and separation of REEs from a range of feedstock compositions. This includes the development of pH and chelator-driven desorption processes for intra-REE separation, including Dy/Nd separation from a range of E-waste derived mixed REE oxides, and Sc, Y, and grouped REE separation from REE ore derived mixed REE oxides. To better facilitate separation process optimization, including the ability to adapt to new/changing feedstocks, we are working toward a predictive model of LanM separations. A unique feature of LanM relative to chemical chelators is that it binds two REEs per protein, which results in the binding of heterogeneous REE pairs (e.g. Nd/Dy vs Nd/Nd), a feature that needs to be accounted for when modeling REE separation performance. Accordingly, we developed and validated a thermodynamic model for cooperative binding by performing equilibrium binding experiments with every pairwise combination of 8 REEs at several concentration ratios. Importantly, the model captures the non-intuitive separation behavior of LanM, where separation factors vary widely based on feed composition, while also accurately predicting the equilibrium state of LanM in the presence of ternary, quaternary, and quinary mixtures of REE. While useful for capturing the equilibrium binding behavior in complex mixtures, the model also reveals intrinsic limitations of the archetypical LanM that we seek to overcome through further exploration of protein variants. To this end, we developed a screening platform that couples high-throughput protein purification with quantitative determination of the intra-REE selectivity profile and used this assay to screen over 900 natural and engineered REE binding proteins. Our screening efforts have resulted in the identification of several variants with promising intra-REE selectivity that will subjected to REE separation tests on column. Collectively, these advances bolster the prospects for using REE binding proteins as a platform for organic solvent-free REE separations. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DEAC52-07NA27344 (LLNL-ABS-858227).