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Radioiodine (129I) poses a risk to the environment due to its long half-life, toxicity, and mobility. It is found at the U.S. Department of Energy Hanford Site due to legacy releases of nuclear wastes to the subsurface where 129I is predominantly present as iodate (IO3 –). To date, a cost-effective and scalable cleanup technology for 129I has not been identified, with hydraulic containment implemented as the remedial approach. Here, novel high-performing sorbents for 129I remediation with the capacity to reduce 129I concentrations to or below the US Environmental Protection Agency (EPA) drinking water standard and procedures to deploy them in an ex-situ pump and treat (P&T) system are introduced. This includes implementation of hybridized polyacrylonitrile (PAN) beads for ex-situ remediation of IO3 –-contaminated groundwater for the first time. Iron (Fe) oxyhydroxide and bismuth (Bi) oxyhydroxide sorbents were deployed on silica substrates or encapsulated in porous PAN beads. In addition, Fe–, cerium (Ce)–, and Bi–oxyhydroxides were encapsulated with anion-exchange resins. The PAN–bismuth oxyhydroxide and PAN–ferrihydrite composites along with Fe- and Ce-based hybrid anion-exchange resins performed well in batch sorption experiments with distribution coefficients for IO3 – of >1000 mL/g and rapid removal kinetics. Of the tested materials, the Ce-based hybrid anion-exchange resin was the most efficient for removal of IO3 – from Hanford groundwater in a column system, with 50% breakthrough occurring at 324 pore volumes. The functional amine groups on the parent resin and amount of active sorbent in the resin can be customized to improve the iodine loading capacity. These results highlight the potential for IO3 – remediation by hybrid sorbents and represent a benchmark for the implementation of commercially available materials to meet EPA standards for cleanup of 129I in a large-scale P&T system.

Revision 1 of this document includes updates to the text and added descriptions of studies that were applied to address some of the data gaps identified in Revision 0. Descriptions of the changes are provided below. Changes to Existing Sections • The summary indicates that Revision 1 contains new information and updated text. • Section 1.0 (introductory paragraph) was updated to indicate that Revision 1 contains new information and updated text. PNNL-24709, Rev. 2 RPT-DVZ-AFRI-030, Rev. 2 vi • Section 2.3.5 was added to describe the results of experiments to evaluate formation of precipitates incorporating iodate during calcite precipitation. Previous literature information about coprecipitation of iodate and calcite from Revision 0 was included in this new section. • Section 3.1.2 was added to describe the results of a vadose zone modeling analysis of the 129 I source areas for the 200-UP-1 operable unit.

CH2M HILL Plateau Remediation Company (CHPRC) is currently developing a 200-West Area groundwater pump-and-treat system as the remedial action selected under the Comprehensive Environmental Response, Compensation, and Liability Act Record of Decision for Operable Unit (OU) 200-ZP-1. This report documents the results of treatability tests Pacific Northwest National Laboratory researchers conducted to quantify the ability of selected activated carbon products (or carbons) to adsorb technetium-99 (Tc-99) from 200-West Area groundwater.

SummaryThe Hanford Site is a former nuclear defense production facility. A groundwater plume containing uranium, originating from a combination of purposeful discharges of wastewater to cribs, trenches, and ponds, along with some accidental leaks and spills related to nuclear fuel fabrication activities, has persisted beneath the Hanford Site 300 Area for many years. Despite the cessation of uranium releases and the removal of shallow vadose zone source materials, the remedial action objective to lower the concentration of groundwater uranium to the U. S. Environmental Protection Agency maximum contaminant level concentration of 30 µg/L has not been achieved within the anticipated 10-year time period. Some unknown amount of contamination remains in the vadose zone beneath the lower extent of the excavation activities. Additional contamination also may remain beneath buildings and facilities in the southern portion of the 300 Area, which has not been decontaminated and decommissioned. The use of polyphosphate technology for source treatment in the vadose zone and capillary fringe is expected to accelerate the natural attenuation of uranium to thermodynamically stable uranium-phosphate minerals. This effort will complement the current 300 Area treatability test being conducted within the saturated zone (e.g., 300 Area aquifer) for in situ treatment of uranium-contaminated groundwater.Polyphosphate technology has been demonstrated for in situ precipitation of phosphate phases to control the long-term fate of uranium. A critical component of the development and testing is detailed evaluation to determine if polyphosphate technology could be modified for infiltration from ground surface or some depth of excavation to stabilize source uranium phases. This report presents results from bench-scale treatability studies conducted under site-specific conditions to optimize the polyphosphate amendment for implementation of a field-scale technology demonstration to stabilize uranium within the 300 Area vadose zone and capillary fringe of the Hanford Site. Documented in this report are data related to 1) the retardation of polyphosphate as a function of water content and pore water velocity, 2) the reaction between uranium-bearing solid phases and aqueous polyphosphate remediation technology as a function of polyphosphate composition and concentration, 3) the mechanism of autunite formation via the reaction of solid-phase calcite-bound uranium and aqueous polyphosphate remediation technology, 4) the transformation mechanism and reaction kinetics between uranyl-carbonate and -silicate minerals with the polyphosphate remedy under advective conditions, and 5) the extent and rate of uranium released and immobilized as a function of polyphosphate composition and the infiltration rate of the polyphosphate remedy. Kinetic rate law parameters were determined from single-pass flow-through experiments. Pressurized unsaturated flow tests were used to determine the effect of polyphosphate composition, concentration, and infiltration rate...

Environmental context. Uranium-phosphate minerals have been identified as a long-term controlling phase that limit the mobility of uranium to groundwater in many contaminated subsurface environments. Complex, coupled processes confound the ability to isolate the rates attributed to individual processes. Results of this investigation provide the necessary information to refine current prediction on the release and long-term fate of uranium in subsurface environments. Abstract. The purpose of this investigation was to conduct a series of single-pass flow-through (SPFT) tests to (1) quantify the effect of temperature (23–90°C) and pH (6–10) on meta-torbernite dissolution; (2) compare the dissolution of meta-torbernite to other autunite-group minerals; and (3) evaluate the effect of aqueous phosphate on the dissolution kinetics of meta-torbernite. Results presented here illustrate meta-torbernite dissolution rates increase by ~100× over the pH interval of 6 to 10, irrespective of temperature. The power law coefficient for meta-torbernite, η = 0.59 ± 0.07, is greater than that quantified for Ca-meta-autunite, η = 0.42 ± 0.12. This suggests the stability of meta-torbernite is greater than that of meta-autunite, which is reflected in the predicted stability constants. The rate equation for the dissolution of meta-torbernite as a function of aqueous phosphate concentration is log rdissol (mol m–2 s–1) = –4.7 × 10–13 + 4.1 × 10–10[PO43–].