# Recovery of rare earth elements from low-grade coal fly ash using a recyclable protein biosorbent

## TL;DR

A new method uses a recyclable protein to recover rare earth elements from coal fly ash, offering a sustainable way to boost clean energy resources.

## Contribution

A recyclable protein biosorbent is developed for selective and efficient recovery of rare earth elements from low-grade coal fly ash.

## Key findings

- The protein biosorbent retains 95% of its initial rare earth element binding capacity after four cycles.
- The method achieves a 100,000-fold increase in rare earth element purity from low-concentration solutions.
- The approach enables sustainable recovery of rare earth elements from industrial waste materials.

## Abstract

Rare earth elements (REEs), including those in the lanthanide series, are crucial components essential for clean energy transitions, but they originate from geographically limited regions. Exploiting new and diverse supply sources is vital to facilitating a clean energy future. Hence, we explored the recovery of REEs from coal fly ash (FA), a complex, low-grade industrial feedstock that is currently underutilized (leachate concentrations of REEs in FA are < 0.003 mol%). Herein, we demonstrated the thermo-responsive genetically encoded REE-selective elastin-like polypeptides (RELPs) as a recyclable bioengineered protein adsorbent for the selective retrieval of REEs from coal fly ash over multiple cycles. The results showed that RELPs could be efficiently separated using temperature cycling and reused with high stability, as they retained ∼95% of their initial REE binding capacity even after four cycles. Moreover, RELPs selectively recovered high-purity REEs from the simulated solution containing one representative REE in the range of 0.0001–0.005 mol%, resulting in up to a 100,000-fold increase in REE purity. This study offers a sustainable approach to diversifying REE supplies by recovering REEs from low-grade coal fly ash in industrial wastes and provides a scientific basis for the extraction of high-purity REEs for industrial purposes.