The 17 REEs consist of the lanthanide group (lanthanum to lutetium in the periodic table), as well as scandium and yttrium. REEs are critical components of many advanced technologies such as magnets, batteries, electronics and catalysts. More importantly, they are also critical for various defense technologies. For instance, they are used in satellites, aircraft, missile guidance systems, batteries & sensors. The worldwide demand for REEs is increasing at a rapid pace. The global supply chain issues compound the problem. China accounts for about 61% of the global supply and 36% of global reserve. The US imports >80% of its REE from offshore suppliers (mainly from China). This has become a national security issue; US supply chain is vulnerable to geopolitical changes and restrictions. The physicochemical similarities of the REEs cause them to co-localize in geological deposits and complicate their separation from each other. Currently, the separation of REEs from their ores and their purification is industrially achieved by solvent extraction and chromatography. While these processes generate REE purities higher than 99%; the reagents, equipment, and energy required to operate these REE separation plants pose technical, economical, and environmental challenges. Current methods are technically complex, time-consuming, expensive and damage the environment. The advent of synthetic biology and modern biotechnology provides alternatives to these processes using biomolecules, particularly proteins. For instance, Lanmodulin (LanM) is a protein that has been shown to have exquisite selectivity for REEs (108 - fold) over other (non-REE) elements. There is also an unmet need for a technology for intra-REE separation. Such a technology is critically important for advancing protein-based metal separation and purification technologies.