Class C fly ash activated by low alkalinity activator with controlled setting

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Structural Behavior of Tc and I Ions in Nuclear Waste Glass

AbstractTechnetium-99 (Tc) and iodine-129 (I) are two long-lived fission products of high volatility, which makes their study in glass structure challenging. Both technetium and iodine have broad ranging multivalent chemistry and complex reactivity dependent on redox conditions; technetium and iodine redox may vary from Tc0 to Tc7+ and from I- to I7+. Relatively few studies have been done on their speciation in glass, in part because of their low retention at the temperatures required for glass melting. To better understand the redox and structural behavior of Tc and I in various nuclear waste glasses, a series of technetium- and iodine-containing borosilicate glasses of varied chemistry were prepared at scales ranging from a few grams to hundreds of kilograms. Technetium was included in both high-level and low-level nuclear waste glass formulations under a variety of redox conditions at concentrations ranging from 0.003 wt% to 0.06 wt%. Non-radioactive iodine glass samples were prepared in crucible melts using excess amounts of sodium or potassium iodide salts or ammonium iodate that resulted in concentrations ranging from 0.04 to 1.27 wt% iodine. These samples were also compared to glasses prepared in pilot-scale experiments in which the overall retentions reached 48% and 34% for technetium and iodine, respectively. Tc and I speciation in the resulting glasses were determined by X-ray absorption spectroscopy (XAS). While technetium was found as Tc0, Tc4+, and Tc7+, only I- was identified in these glasses. Previous studies of Tc local environment information inferred from K-edge XAS and Raman spectroscopy identified pertechnetate tetrahedra surrounded by network-modifying cations in oxidized glasses and octahedral TcO6 units in glasses prepared under reducing conditions. Conversely, iodine K-edge XAS of all glasses studied indicate iodide environments with lithium or sodium nearest-neighbors resembling disordered versions of octahedral sites in crystalline lithium or sodium iodide

Geopolymer waste forms for radioactive wastes

Geopolymer formulations, referred to as ‘DuraLith’, have been developed as candidate waste forms for near-surface disposal of a range of radioactive waste streams in the United States. Examples of these radioactive waste streams include Hanford Low-Activity Waste (LAW), Hanford Secondary Waste (HSW), Sodium Bearing Liquid Waste (SBW) at the Idaho site, and Tank 48H waste at the Savannah River Site. These waste streams exhibit an extremely wide variation in chemical composition and radionuclide content, which pose significant challenges for their solidification and stabilization. In this paper, we will review the development, characterization, and properties of DuraLith geopolymer waste forms for various radioactive waste streams. Metakaolin (MK), blast furnace slag (BFS), and Class F fly ash (FFA) were selected as reactive aluminosilicate materials to produce DuraLith waste forms for these wastes. Numerous composite geopolymers have been investigated, such as FFA/BFS, MK/BFS, and MK/BFS/FFA. The alkaline activator is a tailored solution of the simulated waste stream into which alkali hydroxide and silica fume are dissolved. The testing included key radionuclides such as Tc, I, and Cs, which dominate the risk to the environment. Various enhancers such as tin fluoride and Ag-modified zeolites were employed to improve fixation of radionuclides such has Tc and I. The process of solidification of these radioactive waste streams through geopolymerization was monitored by isothermal calorimetry, rheology, and Vicat needle penetration. Cured geopolymer waste forms were characterized for compressive strength and phase composition and microstructure by XRD and SEM/EDS. Selected samples were tested for leachability of heavy metals and radionuclides after 28 days of curing at ambient temperature according to the ANSI/ANS 16.1 and TCLP leach test procedures. Effects of BFS grades and FFA incorporation on the properties of fresh and hardened waste forms were investigated. Please click Additional Files below to see the full abstract

DuraLith Alkali-Aluminosilicate Geopolymer Waste Form Testing for Hanford Secondary Waste

The primary objective of the work reported here was to develop additional information regarding the DuraLith alkali aluminosilicate geopolymer as a waste form for liquid secondary waste to support selection of a final waste form for the Hanford Tank Waste Treatment and Immobilization Plant secondary liquid wastes to be disposed in the Integrated Disposal Facility on the Hanford Site. Testing focused on optimizing waste loading, improving waste form performance, and evaluating the robustness of the waste form with respect to waste variability

Geopolymer ultrahigh performance concrete: Material and performance

During the last two decades, considerable progress has been made in the development of ultra-high-performance concrete (UHPC) with ordinary Portland cement (OPC). UHPC represents a major development step over high performance concrete (HPC), through the achievement of very high compressive strength (over 20,000 psi or 140 MPa) and superior durability due to very low permeability compared to high-performance concrete; in some cases, fibers are included to achieve improved ductility. Despite these performance advantages, deployment of Portland cement-based UHPC has been slow, in part due to the relatively high compared to that of conventional concrete components. In addition, the higher content of Portland cement in UHPC, high temperature steam curing, and use of relatively large amounts of superplasticizers increase the cost and CO2 footprint. Geopolymer-based UHPCs have the potential for significant advantages over comparable OPC-based materials. We have developed a range of low-cost, low-CO2 footprint, geopolymer UHPC (GUHPC) formulations. The main characteristics of these GUHPCs include: 1) Increased homogeneity by excluding aggregates \u3e9.5mm, 2) Increased packing density through use of micro- and nano-particles, 3) Very low water-to-binder ratio through chemically tailored activator compositions and use of intensive mixing; 4) Composite binders yielding hybrid calcium aluminosilicate hydrate (C-A-S-H) and alkali aluminosilicate hydrate (A-A-S-H) gels to improve product properties; and 5) Regulation of set times using a very effective inorganic retarder. Please click Additional Files below to see the full abstract