Salt waste forms

Fig. 7. Adrenal steroidogenesis in the simple virilizing and salt-wasting forms of congenital adrenal hyperplasia (from Ref. 53, with permission).

The densities of the final waste forms were 1.70 and 1.9 g/cm, and the compression strengths ranged from 1400 to 1900 psi (9.8-11.9 MPa) for both the chloride and nitrate waste forms. These values are significantly higher than the NRC land disposal requirement of 500 psi (3.5 MPa) for cement-based waste forms [17]. Thus, salt waste forms of the CBPC at high loadings are relatively dense hard materials that are suitable for salt waste... 

Hence, for every molecule of ethylene oxide, 1 molecule of salt is formed, creating a waste problem that was traditionally solved by dumping it in a river. Such practice is of course now totally unacceptable. 

Wastes with water content greater than 85% increase the energy costs of the process. Some problems have been noted with phase separations in the final waste form. The technology cannot treat gases or iodine. Mercury is difficult to incorporate. There are concentration limits for some elements in a silicate glass final waste form. Phosphate glass final waste forms can incorporate greater concentrations of some metal oxides, chlorine salts, and mercury in some cases. 

According to researchers, limitations of DC arc systems include the corrosive nature of the vitrified material, limitations on salt and water content, and uncertain performance in the destruction of organic wastes. The addition of flux materials may be required to allow the vitrified material to be poured and to allow the final waste form to meet performance goals. Volatile radionuclides and metals may accumulate in the off-gas treatment system. 

Disorders of 21-hydroxylation account for over 95% of patients with CAH and affect about 1 in 13,000 people. 21-Hydroxylation is catalyzed by P450c21 encoded by a gene CYP21B [95]. The disorder ranges from severe (salt-wasting), when even aldosterone synthesis is prevented, through simple-virilizing, to mild forms, where adequate cortisol is produced. 

This project placed encapsulated spent fuel elements from an experimental AEG reactor into storage holes drilled into the floor of the mine located in a salt bed. Valuable experimental information was obtained about the interaction between the waste form and the salt in which the waste was emplaced. It was in fact this experiment, conducted in 1968, which revealed that inclusions of moisture, or brine, in the salt beds have a tendency to migrate up a thermal gradient towards a heat source placed in the salt. Quantities of brine were measured as migrating to the deposited waste canisters and the interaction of this brine with the canis-tered material was observed. 

There are three issues often raised with regard to the mechanical behavior of the canister-salt-repository system when HLW is the emplaced waste form. 

Electrode selection was based on trial and error. As mentioned in the introduction, no previous studies of electroplating waste mercuric salts without forming amalgams were found. 

The waste acid used for the distillation tests was the effluent from chemical milling operations. The composition was 20 wtZ HNO3, 30 wtZ H2SO4, and 60 g/L U. The H2SO4 can be used to displace NO3 in the metal salts, thus forming sulfate salts, and allows separation of free HNO3 and HF from these salts by distilling them to the overhead stream. 

Energy And Environmental Considerations. The energy requirements to produce malic acid via conventional processes are fairly moderate Malic acid production generates low levels of solid, airborne, and liquid waste. Solid waste is primarily non toxic malic acid salts resulting form regenerating carbon cells and ion-exchanfle resins Airborne emissions ate... 

Again, as in the case of hazardous contaminants discussed in Chapter 16, the solubility of a radioactive contaminant plays a major role in its stabilization in a phosphate matrix. Therefore, one needs to understand the aqueous behavior of a radioactive contaminant prior to selecting the acid-base reaction that will form the CBPC used for fabricating the waste form matrix. In this respect, actinides, fission products, and salts have unique solubility behavior. This behavior is discussed below. 

Details of Salt Waste Streams and their Waste Forms. 

Several additional favorable properties of CBPCs make them an even better candidate for stabilization. The waste form is a dense matrix, generally with very good mechanical properties. Also it is nonleachable, does not degrade over time, is neutral in pH, converts even flammable waste into nonflammable waste forms, performs well within acceptable levels in radiolysis tests, and can incorporate a range of inorganic waste streams (solids, sludge, liquids, and salts). 

High-temperature thermal treatment of hazardous waste offers a reduction in volume as well as a conversion of toxic organic constituents to harmless or less harmful forms [1]. However, hazardous metals can neither be generated nor destroyed in the waste thermal process, but they can be transformed both chemically and physically [2]. There is therefore a potential for hazardous metals to emit if they vaporize at high temperatures [3]. Many matals and their salts will form vapors at temperatures reached by flame and post-flame zones of a combustion chamber. When the vapors cool, they condense to form submicron particles, which tend to be relatively difficult to capture in air polution control equipments. These emissions of submicron metallic particles have been identified as one of the greatest health risks associated with waste incineration [4]. 

In the conceptual waste processing plant, supemate will be separated from sludge because the high salt content of supemate would adversely affect any of the promising waste forms. The sludge will then be dried to convert it to a more easily handled form and washed to remove most of the residual soluble salt. The sludge will then be dried again for incorporation into one of these waste forms. 

Leachability of a waste form is perhaps the most important criterion in considering accident situations. In the absence of salts, some of our cement products may approach the low leachability of glass. After experimenting with several methods for measuring leach rates, we selected the... 

A low-temperature process for conversion of radioactive sodium salt wastes into solid, relatively insoluble, thermally stable sodium aluminosilicates is described. The reaction of the waste (in aqueous solution) with powdered clays such as kaolin, bentonite, halloysite, or dickite produces small crystals (0.5 /xm) of cancrinite. Salts, including radioactive ones, are trapped in the cancrinite crystal lattice. The approximate chemical formula of the cancrinite produced is 2(NaAlSi04) x salt y H2O, with X = 0.52 and y = 0.68 when the entrapped salt is NaNOa. The stoichiometry requires two moles of NaOH for each mole of cancrinite formed. 

All of these complexes, including those with the lanthanide cations, are prepared directly from W04 and the appropriate An" (Ln ), and have only a narrow pH-range of stability (ca5.5-6.5) in aqueous solution. However in the solid state the ammonium salt of [Th(W50is)2] yields the cubic tungsten bronze ThxWOs (x 0.1) when heated in an inert atmosphere to 725°C. It has been proposed that bronzes prepared in such fashion from appropriate POM salts could be used as inert waste forms for actinides and radioactive lanthanides [40]. 

Figure k illustrates in schematic form the precipitation-ion exchange process devised and developed for reducing the actinide concentration of the PRF salt waste, when solidified, to or below 10 nCi/g. This process involves (a) Addition of... 

Extraction of PSA and H5DTPA. Figure 3 also shows the D s for dodecyl sulfuric acid (DSA) (the acidic form of the commonly used detergent, sodium dodecyl sulfate) and diethylenetriamine-pentacetic acid (H5DTPA). Both of these compounds could be constituents in a salt waste treatment facility of a fuel reprocessing plant (1) and therefore were included in the study. 

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