Amrita Bhattacharyya

Biogenic non-crystalline U(IV) revealed as major component in uranium ore genesis
Presenter Amrita Bhattacharyya, LBNL
Session Title Coupled Cycling of Biogeochemical Critical Elements and Contaminants
Abstract Amrita Bhattacharyya, Kate M. Campbell, Shelly Kelly,Yvonne Roebbert, Stefan Weyer, Rizlan Bernier-Latmani and Thomas Borch Historically, uranium (U) ore in sandstone-hosted roll-front deposits is believed to consist primarily of crystalline uraninite (UO2). However, our recent investigation of U roll-fronts at Smith Ranch Highlands, Wyoming suggests that non-crystalline U(IV) may play an important role in U ore genesis. Specifically, this study describes the composition of U within roll-front deposits using an array of biogeochemical techniques, including X-ray absorption spectroscopy, 238U/235U isotope ratio analyses by MC-ICP-MS, and DNA-based (16S rRNA) microbial community analysis. Molecular-scale spectroscopic data indicate between 58 and 92% of U(IV) in the ore zone is composed of non-crystalline U(IV). U isotope analyses reveal that non-crystalline U(IV) is predominantly enriched in 238U, indicating that it is primarily formed via biotic reduction of U(VI) [1,2]. Furthermore, 16S rRNA sequencing data reveal the presence of microorganisms that are likely capable of reducing U(VI) to form non-crystalline U(IV) within these roll-fronts. We present a new conceptual model which depicts the distinct reduction pathways leading to the formation of reduced U(IV) species during roll front deposit genesis. Based on our findings, future research should be focused on understanding the reactivity and mobility of non-crystalline U(IV) within roll-front deposits. [1] Stylo et al. (2015) Proc. Nat. Ac. Sci., doi/10.1073/pnas.1421841112. [2] Stylo et al. (2015) Environ. Sci. Technol. 49, 10553-10561.