(327b) Effective Removal of Pertechnetate (TcO4-), Iodide (I-) and Iodate (IO3-) from Groundwater By Organoclays and Granular Activated Carbon

⁹⁹Tc and ¹²⁹I are major long-life fission products from nuclear power generation. Over the years, Tc and I have been inadvertently introduced into the environment from leaks at waste storage facilities and currently are key risk drivers at the US DOE sites. The most common chemical form of Tc and I in liquid nuclear wastes and in the environment is anionic pertechnetate (TcO₄^-) or iodide (I^-), iodate (IO₃^-) and organo-I. They display limited adsorption onto common sediment minerals and are highly mobile making them difficult to capture or to be immobilized. As the stockpile of ⁹⁹Tc- and ¹²⁹I-bearing nuclear waste continues to increase rapidly, novel sequestration technologies are needed to reduce its potential contamination of the environmental and living organisms.

In this work, inexpensive organoclays and granular activated carbon (GAC) were evaluated for remediation of TcO₄^-, I^- and IO₃^- from groundwater using batch experimental set-up under atmospheric conditions. For TcO₄^-, the adsorption coefficient (K_d) values for the organoclays and GAC samples were greater than 1×10⁵ mL/g, with nearly 100% adsorption. Their adsorption kinetics was fast, completing within 1 hour. The adsorption capacities were >3.2 mg/g over a wide groundwater pH range and under oxic conditions. For I^- and IO₃^-, the adsorption capacities onto the organoclays and GAC in groundwater under oxic condition were high as well: 30 mg/g for I^-, and >100 mg/g for IO₃^-.

Further, Tc K-edge XANES and EXAFS spectra of the organoclays and GAC after Tc adsorption were collected using the beamline 20-BM at the Advanced Photon Source (APS) in order to understand Tc speciation and binding chemistry. Both Tc K-edge XANES and EXAFS spectra indicated that the Tc species bound onto these sorbents is TcO₄^-, rather than its reduced Tc(IV). TcO₄^- is likely bonding with N ligands present in functionalized organic molecules of organoclays or other surface moieties present on GAC. The innovation of this technology is that inexpensive organoclays and GAC can sequester Tc contaminant in the form that it exists naturally in the environment, and an artificial reducing environment is not needed to be created. These results provide an applied solution for treating TcO₄^-, I^- and IO₃^-contamination in the environment or in nuclear wastes.