There is a global legacy of radioactively contaminated land and radioactive wastes, with uranium (U) often considered a key contaminant. Iron (oxyhydr)oxides are ubiquitous in these environments, and as U can incorporate into iron (oxyhydr)oxides, these phases are a potential long term barrier to U migration. Therefore, this project will investigate the stability of U-associated iron (oxyhydr)oxides under fluctuating geochemical conditions. In this project, U(VI)-associated iron (oxyhydr)oxides were exposed to aqueous Fe(II) and HS-, chemical species expected in both GDF and contaminated land environments. A multi-technique approach using XRD, TEM, XAS, luminescence and ICP-MS was then applied. The first study investigated the formation of U(VI)-incorporated goethite, followed by reaction with aqueous Fe(II). U(VI) was incorporated within a structural Fe(III) site, then partially reduced (50% U) to incorporated U(V) in goethite, with no aqueous U released. The second study reacted U(VI)-incorporated goethite with aqueous sulfide, followed by a controlled reoxidation experiment. During sulfidation, U(VI) reduced to U(IV)O2 over time, along with a U(V) component which persisted for several months. Reoxidation resulted in U(VI/V) becoming adsorbed or incorporated into the iron oxyhydroxide phases. In the final study, a high pH sulfidation of U(VI)-adsorbed ferrihydrite led to the formation of aqueous and colloidal U(VI) species, which were stable for the duration of the experiment (6 months). Overall, these studies provided further insight into the efficacy of iron (oxyhydr)oxides as a barrier to U migration in the sub-surface, and demonstrated how common aqueous species (Fe(II) and HS-) may influence U speciation in contaminated land and GDF scenarios.
|Date of Award||1 Aug 2023|
- The University of Manchester
|Supervisor||Samuel Shaw (Supervisor)|
- Fe-atom exchange
- Iron (oxyhdr)oxides