Biorecovery of Rare Earth Elements: Potential Application for Mine Water Remediation

Abstract

Rare earth elements (REEs) are highly valuable due to the complex nature of their extraction from primary and secondary sources. A key feature is that REEs often co-occur with uranium and thorium which, being radioactive, increase the hazard and complexity of REE recovery. A bioprocess which utilizes enzymatically-generated inorganic phosphate to precipitate REEs from solution as their phosphate biominerals is highly effective in the recovery of REEs, effecting rapid recovery onto immobilized bacterial biofilm at high flow-through rates. This also bioprecipitates U and Th. The metal recovery process requires addition of an organic phosphate substrate, e.g. glycerol 2-phosphate (G2P), the cleavage of which provides the inorganic phosphate source for REE biomineralization. G2P is expensive, precluding its large scale use, but early work using uranium showed that tributyl phosphate (TBP) can be used as an alternative phosphate donor molecule. The potential for substitution of G2P by TBP for biorecovery of neodymium is described and a new approach is proposed for enhancing the metal selectivity for REEs against uranium.