Selective Recovery of Rare Earth Elements from Wastes Using Engineered Proteins

Abstract

Rare earth elements (REEs) have become increasingly important materials owing to their use in the high-tech and clean-energy industries. However, the unpredictable supply, possible health risks, and environmentally unsustainable extraction practices associated with REEs have encouraged the development of green technologies for the selective extraction and recovery of metals. This study presents a simple and innovative approach for the selective extraction and recovery of total REEs. Elastin-like polypeptide (ELP) and the REE-binding domain (lanmodulin) are fused to form REEs-sensitive and thermo-responsive genetically encoded ELP called RELP, where ELP offered a reversible, inverse phase transition for repeated uses. The RELP are purified and used for the selective extraction of total REEs from competing non-REEs metals by controlling the solution temperature (4 and 37 °C) and pH. RELP exhibit high REE specificity, even in the presence of non-REE metal ions. The bound REEs are readily recovered during at least six repeated cycles, and the efficiency is maintained. Moreover, REEs are selectively recovered by RELP from steel slag leachate, a potential industrial source of REEs. RELP offers a rapid, selective, and scalable method for REE extraction and recovery. This technology can be adapted to recover other precious metals and commodities. Rare-earth elements (REEs), including the lanthanide series, are crucial components essential for clean energy transitions and originate from geographically limited regions. Exploiting new and more diverse supply sources is imperative to facilitate a clean energy future. Hence, we have explored the recovery of REEs from coal fly ash, a complex, low-grade industrial feedstock that is currently underutilized. Specifically, we demonstrated the thermo-responsive genetically encoded elastin-like polypeptide fused with lanmodulin (RELP) as a recyclable bioengineered protein adsorbent for the selective retrieval of REEs from coal fly ash, which typically contains very low REE levels. RELP efficiently achieves the selective recovery of REEs from fly ash by inducing a phase transition from a solution to a coacervate state through a series of heat-cool cycles (below and above the transition temperature). Successful selective recovery has been demonstrated over multiple cycles. Additionally, RELP has the capability to produce high-purity REEs from sources with extremely low REE concentrations. This study offers a sustainable approach to diversify REE supplies by environmentally friendly management of REE-containing waste and addresses a critical research need for its applications in bio-extracting REEs from fly ash. Lanmodulin is becoming an emerging biological chelator for REEs binding protein. Previous research showed that covalent immobilization of Lanmodulin on supporting materials can be explored as an effective strategy to construct robust and reusable biomaterials for the selective recovery of REEs. However, there are drawbacks associated with these methods as these studies required complex material synthesis and functionalization processes, resulting in reduced protein loading capacity and REEs adsorption activity. There is growing interest in using solid-binding peptides and proteins (SBPs), which recognize and bind to solid surfaces via non-covalent interactions. Here, LanM-PS, a novel recombinant protein, was prepared. PS is a polystyrene binding tag that can specifically bind polystyrene. The biosorbent polystyrene-LanM-PS was obtained by binding of LanM-PS to polystyrene materials. The biosorbent showed adsorption for REEs. With further studies, this environmentally friendly biosorbent can be used as a cost-effective, non-toxic, and reusable material for REEs recovery in batch and continuous operation from low-grade feedstocks.