Waste oxidation

Combustion characteristics of consequence include the overall mechanism of soHd waste combustion, factors governing rates of waste fuels combustion, temperatures associated with waste oxidation, and pollution-formation mechanisms. 

Iron oxide materials and waste oxides Oxygen... 

Most leach rate measurements of both matrix elements and radionuclides were performed at 90 °C using MCC-1 or PCT tests. According to these tests, leach rates range from 10 1 to 10g m 2 d (Lutze 1988). For example, the mass and elemental leach rates (in g-m 2-d ) for the PNL 76-68 glass containing 33 wt% waste oxides were determined at mass - 0.42, Ca - 0.068, Cs - 1.03, Mo - 1.40, Na - 1.32, Sr - 0.075, B - 1.12, and Si - 0.73. These values are typical for borosilicate waste glass as measured by the MCC-1 procedure (90 °C, 28 d). Leach rates of Fe-group elements and ACTs under the same test conditions are considerably lower (10-3 and 10 4g-m 2-d , respectively). 

Fig. 1. Secondary electron micrograph of Na-borosilicate glass loaded with 30 wt% waste oxides and containing 0.9 wt% S03 (etching with 0.1 M HC1). Droplets with chemical durability lower than matrix are a sulphate-enriched phase (Stefanovsky 1989).

Nuclear waste glasses are complex mixtures of more than 30 elements, usually prepared by methods quite different than those used commercially to produce plate glass, for example. Canisters of glass (1-ft-dia x 6-ft-tall) have been prepared by direct furnace melting of a mixture of the waste oxides and an appropriate glass frit. The present experiment simulated this procedure on the laboratory scale. 

Metal or graphite encapsulated waste oxides (0 and U) Atomically dispersed waste oxides in a ceramic titanium dioxide matrix (7>8). 

During development, evaluation of the consolidated materials was based primarily on two criteria, leachability and the concentration factor, i.e., the concentration of waste oxides on a volume basis. The concentration factor is directly affected by the residual porosity in a consolidated waste as well as by the dilution caused by the addition of consolidation aids. This factor can be as high as 1.2 g/cm3 for a fully dense ( 5 g/cm ) titanate waste prepared from the projected Barnwell plant solution composition. The factor is slightly lower for a titanate waste containing silicon and zeolite additions, which has a typical density of U.2 g/cm3. The leachability was determined by an "instantaneous leach test developed for fast, comparative evaluations of materials, the details of which are described elsewhere (l6). 

Figure 2. Transmission electron photomicrograph of a ceramic titanate waste form. The sample was prepared by pressure sintering a titanate fully loaded with fission waste oxides and includes zeolite and silicon additions.

Based on dissolved ions only, the titanate waste showed an overall leach rate of x 10 5 g/cm day and a rate of 5 3 x 10 7 g/cm day for the fission waste oxides only. The results indicate that the leaching which is occurring is associated with the silicate phases in the ceramic, i.e., the Si02 formed from the silicon and the zeolite. The glass samples showed overall leach rates of 6-15 x 10 5 g/cm day and fission waste oxide leach rates of 1.8-2.7 x 10 g/cm day, where the higher rates in both cases were observed in the phosphate-containing glass. 

The waste forms were a fully loaded, pressure sintered titanate waste containing zeolite and silicon additions, a copper boro-silicate glass prepared from Frit 199 supplied by Battelle Northwest Laboratories, and a copper borosUicate glass prepared from the same frit and containing 30% by weight of waste oxides. 

A new process configuration, that for deep-shaft wet-air oxidation, is available as a more satisfactory and economical engineering approach to the application of the wet-oxidation concept (see Figure 9.4-10). The deep-shaft wet-air oxidation reactor is unique to its purpose. The tube-diameter and length are designed so that sufficient reaction time and the desired pressure can be attained during fluid-waste oxidation. The pressure is developed naturally by... 

A flow chart of a generic SCWO process is shown in Figure 10.4. It illustrates the feed stream of a typical aqueous waste. Oxidants such as air, oxygen, or hydrogen peroxide must be provided unless the waste itself is an oxidant. A supplemental fuel source should also be available for low-heat-content wastes. The streams entering the SCWO reactor must be heated and pressurized to supercritical conditions. Influent streams are frequently heated by thermal contact with the hot effluent. Both influent pressure and back pressure must be provided. The influent streams are then combined under supercritical conditions where oxidation occurs. Certain properties of supercritical water make it an excellent medium for oxidation. Acetic acid is generally considered one of the most refractory by-products of the SCWO process of industrial waste. 

Bush and forest fires, burning of agricultural waste Oxidation of hydrocarbons... 

Shaw RW, Dahmen N. Destruction of toxic organic materials using supercritical waste oxidation. J Supercrit Fluids 2000 17 425-437. 

Downey KW, Snow RH, Hazlebeck DA, Roberts AJ. Corrosion and chemical agent destruction, research on supercritical waste oxidation of hazardous military waste. Innovations in Supercritical Fluids, Chapter 21. Washington, D.C. American Chemical Society, 1995. 

Farmer JC, Wang FT, Hawley-Fedder RA, Lewis PR, Summers LJ, Foiles L. Electrochemical treatment of mixed and hazardous wastes oxidation of ethylene glycol and benzene by silver. J Electrochem Soc 1992 139 654-662. 

Oxidants Yield (%), ee (%) Reaction conditions TON Waste (oxidant) (kg kg-1 diol)... 

All of the chromium reagents produce by-products and washings that contain hazardous chromium salts and must be collected as hazardous waste. In many cases, simple oxidants such as household bleach (sodium hypochlorite, NaOCl) can accomplish the same oxidations as chromic acid without using heavy metals, and without generating hazardous waste. Oxidations using sodium hypochlorite involve mildly acidic or basic conditions that may be better than chromic acid for acid-sensitive compounds. 

Natural photosystems have been extensively studied and the machinery of photosynthesis found to be highly modular, organized on multiple scale levels and compartmentalized.32 Importandy, all natural photosystems are molecule-based and their function can be understood both at the schematic level and, in many cases, at the molecular-level. Highly specialized components interact in controlled manner to ultimately deliver a product (reduction equivalents) and to effectively deal with waste (oxidation equivalents). 

Pratt A. R., Nesbitt H. W., and Muir I. J. (1994b) Generation of acids from mine waste oxidative leaching of pyrrhotite in dilute H2SO4 solutions at pH 3.0. Geochim. Cosmochim. Acta 5%, 5147-5159. 

In Walkerworld conditions, an upside-down biosphere occurs. The waste oxidant is held in the sediment and the air contains the reducing power. To sustain a Walkerworld, emissions into... 

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