A Technology for Rare Earth Elements Recovery by Genetically Engineered Elastin-Like Polypeptide

Rare earth elements (REEs) are described as the vitamins of modern industry owing to their use in high-tech and clean-energy industries. Growing concerns of the unpredictable supply, possible health risks, and unsustainable extraction practices demand the development of green technologies for the selective extraction and recovery of REEs. Protein based polymers called elastin-like polypeptides (ELP) were genetically engineered for the selective and repeated recovery of REEs. ELP exhibits a fully reversible thermal coacervation behavior over multiple cycles of cooling and heating and was exploited to enable easy recovery of the bound REEs for repeated use. A lanmodulin protein which exhibits an unusually high affinity and selectivity for REEs was fused to the ELP to provide the highly selective nature to the biopolymers in the presence of higher concentrations of competing non-REEs. Selective binding of REEs was demonstrated at an expected ratio of 2 REE/biopolymer, and minimal binding of competing heavy metals (magnesium and zinc), even at a 300-fold excess, was observed. The REEs were extracted and recovered easily, enabling continuous reuse of the biopolymers. Utility of the biopolymers for REEs recovery from real world samples such as steel slag leachate (≈0.13 mol% REEs) was demonstrated with no decrease in recovery efficiency, the recovery efficiencies of non-REEs were minimal. Results establish the potential of engineered thermoresponsive protein-based polymeric materials as biotechnological tools for environmentally friendly extraction and recovery of REEs with a minimum carbon footprint, which is essential for the sustainability of metal life cycles, from mining to end-of-life to recycling.