The Influence of Glass Leachate on the Hydraulic, Physical, Mineralogical and Sorptive Properties of Hanford Sediment

Abstract

The immobilized low activity waste (ILAW) generated from the Hanford Site will be disposed of in a vitrified form. It is expected that leachate from the vitrified waste will have a high pH and high ionic strength. The objective of this study was to determine the influence of glass leachate on the hydraulic, physical, mineralogical, and sorptive properties of Hanford sediments. Our approach was to put solutions of NaOH, a simplified surrogate for glass leachate, in contact with quartz sand, a simplified surrogate for the Hanford subsurface sediment, and Warden soil, an actual Hanford sediment. Following contact with three different concentrations of NaOH solutions, changes in hydraulic conductivity, porosity, moisture retention, mineralogy, aqueous chemistry, and soil-radionuclide distribution coefficients were determined.Under chemical conditions approaching the most caustic glass leachate conditions predicted in the near field of the ILAW disposal site, approximated by 0.3 M NaOH, significant changes in mineralogy were observed. The clay minerals of the Hanford sediment evidenced the greatest dissolution thereby increasing the relative proportions of the more resistant minerals, e.g., quartz, feldspar, and calcite, in the remaining mass. Some re-precipitation of solids (mostly amorphous gels) was observed after caustic contact with both solids; these precipitates increased the moisture retention in both sediments, likely because of water retained within the gel coatings. The hydraulic conductivities were slightly lower, but because of experimental artifacts, these reductions should not be considered significant. Thus, there does not seem to be large differences in the hydraulic properties of the quartz sand or Warden silt loam soil after 192 days of contact with caustic fluids similar to glass leachate. The long-term projected impact of the increased moisture retention has not been evaluated but likely will not make past simplified performance projections invalid.

Transient and quasi-steady-state dissolution of biotite at 22–25°C in high pH, sodium, nitrate, and aluminate solutions

“…Initial influent solutions were pH 8, similar to the pH typical of uncontaminated Hanford pore waters and groundwater (8.2 Ϯ 0.5, Kaplan et al, 2003). After conditioning for 96 to 500 h in the first set of experiments (prefixed 1, 2, and 3), and 312 h in the second set of experiments (prefixed 5, 6, and 7), the pH 8 influent solutions were replaced with solutions of higher pH (10 to 14).…”

Geochemical Data Package for the 2005 Hanford Integrated Disposal Facility Performance Assessment

“…Following contact with three concentrations of NaOH solutions, Kaplan determined the changes in hydraulic conductivity, porosity, moisture retention, mineralogy, aqueous chemistry, and soil radionuclide distribution coefficients for the contacted solids. Kaplan et al (2003) observed significant changes in mineralogy under chemical conditions approaching the most caustic glass leachate conditions predicted in the near field of the ILAW/IDF site, as approximated by 0.3 M NaOH. The clay minerals in the Hanford sediment underwent the greatest dissolution, thereby increasing the relative proportions of the more resistant minerals, e.g., quartz, feldspar, and calcite, in the remaining sediment.…”

“…The clay minerals in the Hanford sediment underwent the greatest dissolution, thereby increasing the relative proportions of the more resistant minerals, e.g., quartz, feldspar, and calcite, in the remaining sediment. Kaplan et al (2003) detected some reprecipitation of solids (mostly amorphous gels) after caustic contact with both solids. These precipitates increased the moisture retention in both sediments, likely because of water retained within the gel coatings.…”

“…Um and Serne also noted that the new results provide more technical defensibility for past performance assessment predictions that did not use site-specific sediments and/or leachates. Kaplan et al (2003) studied the influence of glass leachate on the hydraulic, physical, mineralogical, and sorptive properties of Hanford sediment. The ILAW generated from the Hanford Site will be disposed as a vitrified waste, and the leachate from this waste will have a high pH and high ionic strength.…”

“…The ILAW generated from the Hanford Site will be disposed as a vitrified waste, and the leachate from this waste will have a high pH and high ionic strength. Kaplan et al (2003) reacted NaOH solutions, a simplified surrogate for glass leachate, with quartz sand, a simplified surrogate for the Hanford subsurface sediment, and Warden soil, an actual Hanford sediment. Following contact with three concentrations of NaOH solutions, Kaplan determined the changes in hydraulic conductivity, porosity, moisture retention, mineralogy, aqueous chemistry, and soil radionuclide distribution coefficients for the contacted solids.…”