Simultaneous Immobilization of Aqueous Co-Contaminants Using a Bismuth Layered Oxide: Implications for In-Situ Remedial Application

Waste sites around the world may contain multiple contaminants, but remediation technologies often only target a single contaminant at a time, even though treatment of one contaminant could result in the mobilization (or immobilization) of another contaminant. At the Hanford Site in southeastern Washington State, multiple contaminants are present in the vadose zone pore water and groundwater including I, Tc, U, and Cr. Use of a bismuth layered oxide as a potential in-situ remediation technology has been gaining attention in recent years due to laboratory tests demonstrating their ability to immobilize contaminants (e.g., I), the relatively low cost of bismuth materials, and the environmentally safe nature of bismuth applications. However, bismuth layered oxides have not been rigorously tested for additional contaminants such as Tc, U or Cr, and especially, have not been tested for simultaneous removal of multiple contaminants. We used a bismuth layered oxide to conduct a series of replicated batch experiments to test removal of multiple contaminants, including Tc, I, Cr, and U, with and without sediment present. The contaminants were tested individually as well as simultaneously at concentrations relevant to the Hanford Site to identify potential co-contaminant interactions. The results demonstrated removal of each of the contaminants separately (98 to 99% aqueous removal), with reduced removal of Tc when the contaminants were combined (from 98% removal when tested individually to 25-90% removal when combined with U, Cr, and/or I). Solid phase characterization is underway, and includes SEM/EDS, QXRD, and BET surface area measurements. The results can be used as a basis for identifying a remedial strategy that addresses the immobilization of multiple contaminants in contaminated vadose zone environments and groundwater.