A Waste Form Based Upon Goethite [alpha-Fe(III) O . OH] and Strengite [Fe(III)PO4 . 2H2O]
EMSL Project ID
35405
Abstract
The objective of this research effort is the development of a waste form that will sequester Tc and I in a matrix that will be resistant to leaching. Goethite (alpha-Fe(III)O . OH) is a low-temperature secondary weathering product of primary iron phases; it is extremely stable at Earth's surface and has little potential for reaction and dissolution. Importantly, Fe appears to co-precipitate with Tc(IV)O2 during goethite formation, or Tc(IV) phases may be incorporated within goethite mineral lattice. Although it is not known where Tc(IV) resides in goethite-technetium solids, it is well-established that the Tc associated with goethite is recalcitrant to re-oxidation and leaching when exposed to oxidizing environments. Strengite [Fe(III)PO4 . 2H2O] is a low-temperature hydrous ferric iron phosphate in the same family as variscite [Al(PO4 . 2H2O], and is extremely stable in near-surface environments. The crystalline lattice of phosphate minerals can accommodate anions, such as I-, into their structure and would be capable of sequestering radioactive 129I. Both goethite and strengite represent plausible stable matrices for retention of Tc and I. Goethite and phosphate minerals have been synthesized for years in the laboratory using well-known recipes. Conditions of synthesis are low temperature and near-neutral pH regimes. There are a wide number of tools available for determining the identity and mineralogical characteristics of solid phases at EMSL/PNNL including, X-Ray Diffraction (XRD), micro-XRD, Mossbauer Spectroscopy (MS), Selected Area Electron Diffraction (SAED), Scanning Electron Microscopy (SEM), SEM combined with Focused Ion Beam (FIB), Transmission Electron Microscopy (TEM) and Energy Dispersive Spectroscopy (EDS). Data collected from these characterization studies will be combined with data collected in a number of X-ray Absorption Spectroscopy (XAS) stations (beam lines) around the country to determine the oxidation state, bond lengths, and number of coordinating oxygen atoms for Tc. In addition, different tests will be conducted with waste forms in order to determine the retention of Tc and I. We will use batch, column and microfluidic techniques, as well as, the single-pass flow-through (SPFT) method to parameterize the kinetic rate equation, which can then be directly incorporated into computer modeling-based Performance Assessments routinely used at Hanford. Release of Tc and I to solution will be quantified using inductively-coupled plasma mass spectroscopy (ICP-MS) and we have recently made successful quantification of low concentrations of technetium (<0.1 ppb) and iodine (<10 ppb) in our analysis routine. We will also quantify dissolution rates of sparingly soluble solids in water using a new technique called vertical scanning interferometry (VSI). Once the dissolution characteristics of the goethite-based waste form have been worked out, then the chemical durability can be compared against that of other candidate waste forms. In particular, we expect that the surface area of the goethite will be vastly different from that of grout. Because of the importance of determining the dissolution rate dependence on surface area, experiments will have to be designed to take this parameter into account. When performed under uniform set of conditions, the comparison tests will be a fair assessment of the relative chemical corrosion resistance of all the candidate waste forms.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2009-10-06
End Date
2012-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
Related Publications
Um W, HS Chang, JP Icenhower, RJ Serne, N Qafoku, JH Westsik, Jr, EC Buck, RK Kukkadapu, SC Steven, WW Lukens, and CJ Dodge. 2011. "Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation ." Environmental Science & Technology 45:4904–4913.
Um W, HS Chang, JP Icenhower, RJ Serne, N Qafoku, JH Westsik, Jr, EC Buck, RK Kukkadapu, SC Steven, WW Lukens, and CJ Dodge. 2011. "Immobilization of 99-Technetium (VII) by Fe(II)-Goethite and Limited Reoxidation ." Environmental Science & Technology 45:4904–4913.
Um W, HS Chang, JP Icenhower, WW Lukens, RJ Serne, N Qafoku, RK Kukkadapu, and JH Westsik, Jr. 2012. "Iron Oxide Waste Form for Stabilizing 99Tc." JNMM. Journal of Nuclear Materials Management 429(1-3):201-209 . doi:10.1016/j.jnucmat.2012.06.004
Wang G, and W Um. 2012. "Mineral Dissolution and Secondary Precipitation on Quartz Sand in Simulated Hanford Tank Solutions Affecting Subsurface Porosity." Journal of Hydrology 472-473:159-168. doi:10.1016/j.jhydrol.2012.09.021
Wang G, and W Um. 2013. "Facilitated Strontium Transport by Remobilization of Strontium-Containing Secondary Precipitates in Hanford Site Subsurface." Journal of Hazardous Materials 248-249:364-370. doi:10.1016/j.jhazmat.2013.01.021