Stuart D. Ware

Bio: Stuart D. Ware is an academic researcher from Los Alamos National Laboratory. The author has contributed to research in topics: Uranium & Sorption. The author has an hindex of 5, co-authored 7 publications receiving 101 citations.

Anion Exchange Resins for the Selective Separation of Technetium from Uranium in Carbonate Solutions

Abstract: In alkaline carbonate solutions both technetium and uranium exist as anionic species, TcO4– and UO2(CO3)34–, which makes separating Tc and U from each other more challenging compared to acidic PUREX type solutions where uranium forms neutral or cationic complexes. We tested the batch separation of 99Tc, 238U, and 239Pu from carbonate solutions using anion exchange resins with different properties, including Purolite A530E, Reillex HPQ, and Dowex Marathon WBA. Overall, the highest Kd values for pertechnetate were achieved using the strong base resins in solutions of the lowest carbonate concentration. Pretreating the resins in higher carbonate concentrations before use was shown to increase the Kd values for pertechnetate. The measured Kd values for uranium generally were low, resulting in high selectivity for the separation of pertechnetate from uranium in carbonate solutions.

Treatability Study of Reactive Materials to Remediate Groundwater Contaminated with Radionuclides, Metals, and Nitrates in a Four-Component Permeable Reactive Barrier

Abstract: Publisher Summary This chapter presents a treatability study of a shallow multicontaminant plume of 239,240Pu, 241Am, 90Sr, nitrate, and perchlorate in Mortandad Canyon, Los Alamos, New Mexico, by using a multiple permeable reactive barrier consisting of four sequential layers These layers include a polyelectrolyte-impregnated porous gravel for flocculating colloids, an Apatite II layer for plutonium, americium, and strontium immobilization, a layer of pecan shells as a biobarrier to nitrate and perchlorate; and a limestone gravel layer for any anionic species that may slip through the other layers, especially those of americium-carbonate The pecan shells sorb strontium very well and the Apatite II remediates nitrate and perchlorate very well Nitrate, perchlorate, plutonium americium, and 90Sr concentrations are reduced to below their maximum concentration limits (MCL) and usually to below detection limits in laboratory studies The materials for this particular multiple barrier are inexpensive and readily available, and thus a large amount can be used to ensure conservative performance If the barrier performs as well as desired in the field, the total expected inventory of radionuclides in the shallow aquifer is low enough that complete removal by huge of barrier material does not result in activities high enough for the barrier to become a hazardous or radioactive waste The nitrate and perchlorate are reduced to harmless components and does not cause the barrier to become a hazardous waste

Mini-columns for Conducting Breakthrough Experiments. Design and Construction

Abstract: Experiments with moderately and strongly sorbing radionuclides (i.e., U, Cs, Am) have shown that sorption between experimental solutions and traditional column materials must be accounted for to accurately determine stationary phase or porous media sorption properties (i.e., sorption site density, sorption site reaction rate coefficients, and partition coefficients or Kd values). This report details the materials and construction of mini-columns for use in breakthrough columns to allow for accurate measurement and modeling of sorption parameters. Material selection, construction techniques, wet packing of columns, tubing connections, and lessons learned are addressed.

The geochemistry of acid mine drainage

Abstract: Mining and mineral processing generates large volumes of waste, including waste rock, mill tailings, and mineral refinery wastes. The oxidation of sulfide minerals in the materials can result in the release of acidic water containing high concentrations of dissolved metals. Recent studies have determined the mechanisms of abiotic sulfide-mineral oxidation. Within mine wastes, the oxidation of sulfide minerals is catalyzed by microorganisms. Molecular tools have been developed and applied to determine the activity and role of these organisms in sulfide-mineral-bearing systems. Novel tools have been developed for assessing the toxicity of mine-waste effluent. Dissolved constituents released by sulfide oxidation may be attenuated through the precipitation of secondary minerals, including metal sulfate, oxyhydroxide, and basic sulfate minerals. Geochemical models have been developed to provide improved predictions of the magnitude and duration of environmental concerns. Novel techniques have been developed to prevent and remediate environmental problems associated with these materials.

Identifying the Recognition Site for Selective Trapping of 99TcO4– in a Hydrolytically Stable and Radiation Resistant Cationic Metal–Organic Framework

Abstract: Effective and selective removal of 99TcO4– from aqueous solution is highly desirable for both waste partitioning and contamination remediation purposes in the modern nuclear fuel cycle, but is of significant challenge. We report here a hydrolytically stable and radiation-resistant cationic metal–organic framework (MOF), SCU-101, exhibiting extremely fast removal kinetics, exceptional distribution coefficient, and high sorption capacity toward TcO4–. More importantly, this material can selectively remove TcO4– in the presence of large excesses of NO3– and SO42–, as even 6000 times of SO42– in excess does not significantly affect the sorption of TcO4–. These superior features endow that SCU-101 is capable of effectively separating TcO4– from Hanford low-level waste melter off-gas scrubber simulant stream. The sorption mechanism is directly unraveled by the single crystal structure of TcO4–-incorporated SCU-101, as the first reported crystal structure to display TcO4– trapped in a sorbent material. A recogni...

Efficient and Selective Uptake of TcO4– by a Cationic Metal–Organic Framework Material with Open Ag+ Sites

Abstract: 99Tc is one of the most problematic radioisotopes in used nuclear fuel owing to its combined features of high fission yield, long half-life, and high environmental mobility. There are only a handful of functional materials that can remove TcO4– anion from aqueous solution and identifying for new, stable materials with high anion-exchange capacities, fast kinetics, and good selectivity remains a challenge. We report here an 8-fold interpenetrated three-dimensional cationic metal–organic framework material, SCU-100, which is assembled from a tetradentate neutral nitrogen-donor ligand and two-coordinate Ag+ cations as potential open metal sites. The structure also contains a series of 1D channels filled with unbound nitrate anions. SCU-100 maintains its crystallinity in aqueous solution over a wide pH range from 1 to 13 and exhibits excellent β and γ radiation-resistance. Initial anion exchange studies show that SCU-100 is able to both quantitatively and rapidly remove TcO4– from water within 30 min. The exc...

Mechanism unravelling for ultrafast and selective 99TcO4− uptake by a radiation-resistant cationic covalent organic framework: a combined radiological experiment and molecular dynamics simulation study

Abstract: 99Tc is one of the most problematic fission products in the nuclear fuel cycle owing to its large inventory in used nuclear fuel, long half-life, potential radiation hazard, high environmental mobility of its major species 99TcO4−, and its redox-active nature. Ideally, 99TcO4− should be removed at the first stage, when the used fuel rods are dissolved in highly concentrated nitric acid solution, which can substantially reduce its interference with the solvent extraction process through catalytic redox reactions with the key actinides and diminish the chance of discharge into the environment as the volatile species during the waste vitrification process. However, this task cannot be achieved by any of the reported anion-scavenging materials including traditional polymeric anion-exchange resins, inorganic cationic framework materials, and recently developed cationic metal–organic framework materials, because they either are not stable under the extreme conditions of the combined high acidity and strong radiation field or do not possess the required uptake selectivity towards 99TcO4− in the presence of a huge excess of competing anions such as NO3− and SO42−. Herein, we present the first study of 99TcO4− removal under extreme conditions by a two-dimensional conjugated cationic covalent organic framework material, SCU-COF-1. This material exhibits ultrahigh acid stability, great resistance towards both large-dose β and γ irradiation and unprecedented 99TcO4− uptake capabilities including extremely fast sorption kinetics (sorption equilibrium can be reached within 1 min), ultrahigh uptake capacity (702.4 mg g−1 for the surrogate ReO4− at a slightly elevated temperature), and good anion-exchange selectivity towards 99TcO4−. These excellent features endow SCU-COF-1 with the practical capabilities of separating 99TcO4− from both simulant highly acidic fuel reprocessing solutions (3 M nitric acid) and low-activity waste streams at the US legacy nuclear site. The anion-exchange mechanism and the 99TcO4− uptake selectivity are further demonstrated and clearly visualized by the molecular dynamics simulation investigations.