Bacterial-facilitated uranium transport in the presence of phytate at Savannah River Site.

At the Department of Energy (DOE) managed Savannah River Site (SRS), uranium and other heavy metals continue to pose threats to the ecosystem health and processes. In the oxic soil of this site, uranium is present primarily as soluble salts of the uranyl ion (i.e., U(VI) or UO ₂ ²⁺ ). Although UO ₂ ²⁺ has a strong sorption to the soil, the mobile indigenous bacteria may facilitate its transport. On the contrary, precipitation of UO ₂ ²⁺ with phosphate has been found to be an alternative remediation strategy. This research investigated the effects of mobile bacteria and phytate on UO ₂ ²⁺ transport at SRS in column experiments. It was discovered that UO ₂ ²⁺ can barely be mobilized by de-ionized water but can be significantly transported with the aid of mobile indigenous bacteria. UO ₂ ²⁺ had the most facilitated transport observation when it reached equilibrium with the bacteria before the transport. When UO ₂ ²⁺ and bacterial were introduced to the soil at the same time or UO ₂ ²⁺ was pre-deposited in the soil, the facilitated transport was less pronounced. In the presence of phytate, bacterial-facilitated UO ₂ ²⁺ transport was hindered. pH was found to play the key role for UO ₂ ²⁺ immobilization in the presence of phytate. The immobilization of UO ₂ ²⁺ with the addition of phytate increased with the increase of pH within the pH range of this study because of the impact of pH on the solubility of UO ₂ (OH) ₂ . Phytate promoted UO ₂ ^- -PO ₄ ^3- complex and/or [Ca(UO ₂ ) ₂ (PO ₄ ) ₂ ] formation, leading to enhanced UO ₂ ²⁺ immobilization in the SRS soil.
(Published by Elsevier Ltd.)