SO(2) Removal from Flue Gases Using Uutility Synthesized Zeolites

Historically, sulfur dioxide (SO{sub 2}) emissions were unregulated. As the environmental consequences of such emissions began to surface, increasingly stringent, federal and state government mandated pollution control requirements were imposed on the electric power generating industry. Coal burning utilities were forced to make one of two dioices. They could install flue gas scrubbing equipment or start to burn lower sulfur containing coal. The proposed research is directed at those utilities that have made the second choice, or utilities desiring to undertake new plant construction

A model for reactive porous transport during re-wetting of hardened concrete

A mathematical model is developed that captures the transport of liquid water in hardened concrete, as well as the chemical reactions that occur between the imbibed water and the residual calcium silicate compounds residing in the porous concrete matrix. The main hypothesis in this model is that the reaction product -- calcium silicate hydrate gel -- clogs the pores within the concrete thereby hindering water transport. Numerical simulations are employed to determine the sensitivity of the model solution to changes in various physical parameters, and compare to experimental results available in the literature.Comment: 30 page

SO(2) Removal from Flue Gases Using Uutility Synthesized Zeolites

Historically, sulfur dioxide (SO{sub 2}) emissions were unregulated. As the environmental consequences of such emissions began to surface, increasingly stringent, federal and state government mandated pollution control requirements were imposed on the electric power generating industry. Coal burning utilities were forced to make one of two dioices. They could install flue gas scrubbing equipment or start to burn lower sulfur containing coal. The proposed research is directed at those utilities that have made the second choice, or utilities desiring to undertake new plant construction

An investigation of the structure and phase relations of C-S-H gels. Final report, August 15, 1991--September 14, 1997

Solid state NMR was used to obtain data on the atomic level structure of calcium silicate hydrate (C-S-H) that formed from a variety of starting materials under a variety of conditions. Because C-S-H is the major component of hydrated portland cement, a knowledge of its structure and of its structural evolution will ultimately allow users of cement containing materials such as mortars and concrete to more accurately predict the physical and mechanical behavior of these materials once they are placed into service. From the outset, the goal of the work was to observe the hydration process on the atomic level, integrate the findings with existing data in the literature, and refine hydration models as necessary to accommodate the newly acquired data

Physical, Chemical and Structural Evolution of Zeolite-Containing Waste Forms Produced from Metakaolinite and Calcined HLW

Natural and synthetic zeolites are extremely versatile materials. They can adsorb a variety of liquids and gases, and also take part in cation exchange reactions. Zeolites are easy to synthesize from a wide variety of natural and man made materials. One combination of starting materials that exhibits a great deal of promise is a mixture of metakaolinite and/or Class F fly ash and concentrated sodium hydroxide solution. Once these ingredients are mixed and cured at elevated temperatures, they react to form a hard, dense, ceramic-like material that contains significant amounts of crystalline tectosilicates (zeolites and feldspathoids). Zeolites have the ability to sequester ions in lattice positions or within their networks of channels and voids. As such they are nearly perfect waste forms, the zeolites can host alkali, alkaline earth and a variety of higher valance cations. In addition to zeolites, it has been found that the zeolites are accompanied by an alkali aluminosilicate hydrate matrix that is a host, not only to the zeolites, but to residual amounts of insoluble hydroxide phases as well. A previous publication has established the fact that a mixture of a calcined equivalent ICPP waste (sodium aluminate/hydroxide solution containing {approx}3:1 Na:Al) and fly ash and/or metakaolinite could be cured at various temperatures to produce a monolith containing Zeolite A (80 C) or Na-P1 plus hydroxy sodalite (130 C) crystals dispersed in an alkali aluminosilicate hydrate matrix. Dissolution tests have shown these materials (so-called hydroceramics) to have superior retention for alkali, alkaline earth and heavy metal ions. The zeolitization process is a simple one. Metakaolinite and/or Class F fly ash is mixed with a caustic sodium-bearing calcine and enough water to make a thick paste. The paste is transferred to a metal canister and ''soaked'' for a few hours at 70-80 C prior to steam autoclaving the sample at {approx}200 C for 6-8 hours. The waste form produced in this fashion could be a viable alternative for fixation of low activity waste (LAW) calcines. Our objective is to adapt this technology for use in site remediation and clean up of caustic waste solutions now in storage in tanks at Hanford and the Savannah River sites. The proposed work is meant to develop a clearer understanding of the advantages and limitations of producing a zeolite-containing waste form (hydroceramic) from calcined radioactive waste, i.e. the effect of processing variables, reaction kinetics, crystal and phase chemistry, and microstructure on their performance

Hydroceramic Binders

This presentation was given at the DOE Office of Science-Environmental Management Science Program (EMSP) High-Level Waste Workshop held on January 19-20, 2005 at the Savannah River Site

Preparation and Properties of Hydroceramic Waste Forms Made with Simulated Hanford Low-Activity Waste

Approximately 85 million gallons of high-level waste (HLW) is currently stored in underground tanks at the Hanford Reservation and the Savannah River Site (SRS). The waste consists of a hydroxide-rich precipitate (sludge) and a sodium-rich supernate. The supernate is a NaOH rich solution containing lesser amounts of NaNO 3 and NaNO 2 and small amounts of soluble fission products, cladding materials, and organics (volatile organics and semi-volatile organics known as VOCs and SVOCs). The Department of Energy (DOE) has chosen glass as its waste form for both sludge and sodium-rich supernate. However, because of the volume of the supernate, alternatives to vitrification are being sought for some of this waste. One alternative is to remove 137 Cs and 90 Sr from the supernate. Decontaminating the waste in this way allows the waste to be designated as low-activity waste (LAW) and as such the waste now becomes eligible for solidification and disposal on site. SRS is solidifying its LAW with a blended Portland cement forming Saltstone. Hanford has been considering a bulk vitrification process in which the LAW will be mixed with Hanford soil and vitrified in place in a disposable carbon-arc powered glass melter/waste container. Both waste forms can then be buried on site in appropriate vaults or low-level waste land fills. A hydroceramic is an alternative waste form designed to solidify and stabilize LAW that is made from metakaolin plus NaOH and/or NaOH rich LAW supernate. In addition to NaOH, LAW can contain a wide range of sodium nitrate and sodium nitrite concentrations. Although a hydroceramic waste form can be made directly from some types of decontaminated waste, e.g., those that are highly alkaline (8-12M NaOH) and contain less than 25 mol% of NO x (NO x is used as the short-note for nitrates and nitrites in this article.) relative to the total Na in the waste, by simply mixing the LAW with metakaolin and curing the resulting paste at 901C, the remaining LAW, especially that stored at Hanford must be pretreated in some way before it can be similarly solidified; the relative molar proportion of NO x /Na must be reduced to 25% or less. In this paper calcination is evaluated as a potential pretreatment method for Hanford AN-107 (AN-107 is a waste storage tank on Hanford site) LAW, but in choosing this method it is necessary to divide the preparation of the hydroceramic waste form into two steps: denitration/denitrition of the liquid waste stream to produce a granular calcine followed by solidification using a metakaolin plus 4M NaOH binder. A simulated Hanford AN-107 LAW was calcined at 3751, 4501, 5251, 6001, and 6751C in the presence of sucrose and metakaolin added as a calcination aid. It was shown that the leachability of the calcines decreased as calcination temperature increased, i.e., the waste form became more crystalline. In the second step, each of the granular calcines was mixed with additional metakaolin and just enough 4M NaOH to form a thick paste. The paste was precured at 401C and then autoclaved at 901C to form a monolith. X-ray diffraction and scanning electron microscopy characterization showed that the calcines themselves contained an amorphous phase and crystalline hydroxysodalite, and that the hydroceramics made from these calcines plus additional metakaolin/NaOH binder consisted predominantly of zeolite A and hydroxysodalite. The temperature used to prepare the calcines not only affected the properties of the calcines, but those of the monolithic hydroceramics as well. Experimental results demonstrated that 5251C represented the optimal temperature for producing the most suitable calcine for subsequent solidification with metakaolin and 4M NaOH. The resulting hydroceramic nuclear waste form was strong and had the lowest overall leachability. The leachability of the hydroceramic is normally lower than that of the corresponding calcines up to B6001C. The product consistency test (PCT) determined normalized release rate NR Na for the hydroceramic (0.14 g/m 2 . day) was comparable to similar leach rates determined for Hanford's low-activity waste reference material glass (0.08 g/m 2 . day) and a steam reformed calcine made with Hanford's AN-107 tank waste (0.25 g/m 2 . day)

Selection and durability of seal materials for a bedded salt repository: preliminary studies

This report details preliminary results of both experimental and theoretical studies of cementitious seal materials for use in a proposed nuclear waste repository in bedded salt. Effects of changes in bulk composition and environment upon phase stability and physical/mechanical properties have been evaluated for more than 25 formulations. Bonding and interfacial characteristics of the region between host rock and seal material or concrete aggregate and cementitious matrix for selected formulations have been studied. Compatibilities of clays and zeolites in brines typical of the SE New Mexico region have been investigated, and their stabilities reviewed. Results of these studies have led to the conclusion that cementitious materials can be formulated which are compatible with the major rock types in a bedded salt repository environment. Strengths are more than adequate, permeabilities are consistently very low, and elastic moduli generally increase only very slightly with time. Seal formulation guidelines and recommendations for present and future work are presented. 73 references, 25 figures, 61 tables