(449bu) Toward Radical Improvements in Biosorption Technology for Rare Earth Elements

Bennett Carv, Soumya Srivastava, and James Moberly

Rare earth elements (REE) are essential to many electronic products, â??greenâ? energy technologies, and medical imaging and diagnostics. These elements are desirable for their unique properties that include magnetism, phosphorescence, and catalytic ability. While very little quantities are needed to support the technology for which they are used, growing demand for these products is causing concern about economic availability of these critical materials. Though REE are relatively abundant in the Earth's crust, their similar chemical behavior makes separation of these elements an energy intensive process that generates considerable waste. As such, an efficient and economical method is required to be able to recover these elements from end-of-life products and other waste streams toward a â??closedâ? REE cycle. However, currently employed technologies for separations of REE from waste streams is not yet competitive with terrestrial sources. Biosorption is a â??greenâ? process which may lend itself to inexpensive selective removal of REEs, but much work is needed to improve this separation processes.

Microfluidic devices are one means that may allow for the rapid separation and later identification of organisms that are capable of selectively accumulating REE, also known as organisms which hyperaccumulate metals (OHMs). Microfluidic devices purposed for OHM separation may also be capable of deployment as a unit process designed for continuous separation. However, a fundamental understanding of the mechanism of metal accumulation in model organisms and their response to conditions that may occur during separation are needed to develop this promising technology. The ability to quickly identify and select relevant OHMs and operating parameters under process stream conditions may enable biosorption to further mature as a separation technology.

The current research focused on Cupriavidus necator as a model organism for study. Previous studies with C. necator have focused on its capability to biologically precipitate and accumulate different metals including yttrium, palladium, silver, germanium, cobalt, nickel, mercury, zinc, copper, lead, and cadmium. Our data suggest that C. necator is able to selectively accumulate light REE compared to heavy REE. Additionally, these studies evaluated changes in REE accumulation and physical properties of C. necator with pH and temperature gradients to better understand the behavior of C. necator and the accumulated REE during continuous or extended separation processes within microfluidic devices. These results provide valuable information that will assist in the further development of microfluidic devices to be deployed for biosorption processes.