Subsurface Bio-Immobilization of Plutonium: Experimental and Model Validation Study

Technical Report · Tue Jan 03 04:00:00 EST 2012

OSTI ID:935784

Deo, Randhir P. ^[1]; Rittmann, Bruce E. ^[2]; Reed, Donald T. ^[3]

---

1. Arizona State Univ., Tempe, AZ (United States); Arizona State University
2. Arizona State Univ., Tempe, AZ (United States)
3. Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)

We conducted a coordinated experimental and modeling study centered on the interaction of Shewanella alga BrY (S. alga) with plutonium species and phases. Plutonium is the key contaminant of concern at several DOE sites that are being addressed by the overall ERSP program. The over-arching goal of this research was to understand the long-term stability of bio-precipitated "immobilized" plutonium phases under changing redox conditions in biologically active systems. To initiate the process of plutonium immobilization, a side-by-side comparison of the bioreduction of uranyl and plutonyl species was conducted with S. alga. Uranyl was reduced in our system, consistent with literature reports, but we noted coupling between abiotic and biotic processes and observed that non-reductive pathways to precipitation typically exist. Additionally, a key role of biogenic Fe²⁺, which is known to reduce uranyl at low pH, is suggested. In contrast, residual organics, present in biologically active systems, reduce Pu(VI) species to Pu(V) species at near-neutral pH. The predominance of relatively weak complexes of PuO₂⁺ is an important difference in how the uranyl and plutonyl species interacted with S. alga. Pu(V) also led to increased toxicity towards S. alga and is also more easily reduced by microbial activity. Biogenic Fe²⁺, produced by S. alga when Fe³⁺ is present as an electron acceptor, also played a key role in understanding redox controls and pathways in this system. Overall, the bioreduction of plutonyl was observed under anaerobic conditions, which favor its immobilization in the subsurface. Understanding the mechanism by which redox control is established in biologically active systems is a key aspect of remediation and immobilization strategies for actinides when they are present as subsurface contaminants.

• Research Organization: Arizona State Univ., Tempe, AZ (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: FG02-05ER64033
• OSTI ID: 935784
• Report Number(s): 0011190
• Country of Publication: United States
• Language: English

Related Subjects

59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.