Molten salt destruction

The incineration is accomplished by injecting the hazardous material and air beneath the surface of a pool of molten salts. Typically, sodium carbonate with a small amount (1 to 10%) of sodium sulfate is used as the molten salt, however, other alkali metal carbonates or mixtures of alkali metal carbonates can be employed. Sodium carbonate is used because it reacts instantly with acidic gases to form sodium salts. The small amount of sodium sulfate is used to catalyze the combustion of carbon. Temperatures of the molten salts are usually in the 700° to 1000°C range. 

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Johanson, J. G. Yosim, S. J. Kellogg, L. G. Sudar, S. "Elimination of Hazardous Wastes by the Molten Salt Destruction Process," Proc. 8th Annu. Res. Symp. Incineration and Treatment of Hazardous Waste, EPA-600/9-83-003,... 

Molten Salt Destruction The molten salt destruction (MSD) tests were performed at LLNL. The experiments were conducted in a small-scale MSD unit (about 1 kg/hr). The molten salts used were a mixture of sodium, potassium, and lithium carbonates at approximately 750°C. The explosive was fed to the unit in a slurry with water (typically 35 wt % explosive). The slurry was moved to a nozzle with a peristaltic pump. At the nozzle, a high-velocity airstream (driver gas) quickly carried the explosive/water mixture through a nozzle and into the salt. The entire operation was conducted remotely. The air used as the driver gas provided most or all of the oxygen for oxidation of the waste. 

The results in either mode of operation of the solids recirculation system with LGP do not compare favorably with molten salt destruction (MSD). Only 0.58% of injected nitrogen is emitted as oxide and 0.11% of injected carbon is emitted as CO in MSD. This represents a major reduction in emitted pollutants for MSD. 

Explosives Using the Molten Salt Destruction Process," Lawrence Livermore National Laboratory, University of California, Livermore, CA, 23rd International Annual Conference of ICT, Karlsruhe, Germany (June 30-July 3, 1992). 

Several other technologies (e.g., molten-salt destruction) are being used at research and development sites (e.g., Eglin Air Force Base and Strauss Avenue Thermal Treatment Plant) to destroy energetic materials, but these technologies are not an integral part of DOD s plan for the demilitarization of obsolete munitions. 

Using lower temperatures than conventional combustion (but longer residence times), molten-salt destruction has achieved 99.9999% PCB destruction efficiency. The salt is typically sodium carbonate (Na2C03). Because emitted particles and vapors are absorbed or react with the salt, fewer emmission controls are necessary. The process destroys liquid or "solid" PCB however, the salt bed may subsequently become contaminated by noncombustible residue. 

The molten salt electrolyte also contributes to the safety behavior of ZEBRA cells. The large amount of energy stored in a 700 g cell, which means about 30 kWh in a 300 kg battery, is not released suddenly as heat as be expected in a system with liquid electrodes such as the sodium sulfur cell. In the case of accidental destruction of ZEBRA cells, the sodium will react mainly with the molten salt, forming A1 sponge and NaCl. -The diffusion of the NaAICI ... 

Molten salt is a technique that has been considered for the destruction of pesticides and other hazardous wastes for several years. In a recent study by Rockwell International for EPA (1 ), the destruction of solid hexachlorobenzene (HCB) and liquid chlordane exceeded 99.99% in a molten sodium carbonate bath at 900 to 1000°C with a residence time of 0.75 s. For the pilot-scale tests, the concentration of HCB and chlordane in the spent melt was < 1 ppm. The HCl concentration in the off-gas was < 100 ppm. 

The pesticide industry generates many concentrated wastes that are considered hazardous wastes. These wastes must be detoxified, pretreated, or disposed of safely in approved facilities. Incineration is a common waste destruction method. Deep well injection is a common disposal method. Other technologies such as wet air oxidation, solvent extraction, molten-salt combustion, and microwave plasma destmction have been investigated for pesticide waste applications. 

The chemistry of molten salts as nonaqueous solvent systems is one that has developed extensively from the 1960s till the present, and only a brief survey can be given here. The most obvious difference when compared with the chemistry of aqueous solutions are the strongly bonded and stable nature of the solvent, a concomitant resistance to destruction of the solvent by vigorous reactions, and higher concentrations of vanous species, particularly coordinating anions, than can be obtained in saturated solutions in water. 

Five separate destruction technologies were tested for the destruction of waste HMX and PBX high explosives (HE). Since incineration is the baseline technology, a series of tests was conducted at a commercial two-stage, fixed-hearth incinerator. Destruction by molten salt injection was tested at LLNL. The last three destruction techniques are based on a base hydrolysis (BH) explosive pretreatment to produce a nonexplosive solution for further treatment. Three secondary treatments for BH were tested, including hydrothermal, biodegradation, and thermal decomposition. BH and hydrothermal techniques were tested at Los Alamos National Laboratory (LANL), and LLNL tested biological and thermal decomposition. 

Incineration is cited exclusively as a method of destruction, applicable to neat compounds or waste solvents. Other thermal methods, such as molten metal salt treatment, which involves intimate contact with a molten salt, such as AI2O3 (Shultz 1985), are suitable. Chemical processes that may be effective are wet air oxidation, electrochemical oxidation, and catalytic destruction. Ketones in aqueous wastes can be altered to innocuous gases by heating at 300-460°C (572-860°F) and 150-400 atm pressure with or without catalyst. Ni and Fc203 were found to be effective catalysts in such thermal treatments (Baker and Sealock 1988). 

Incineration or molten salt treatment are suitable methods for its destruction. 

At high temperatures, the structures of engine turbines are exposed not only to oxygen but also to other constituents in the form of gas such as CO2 and SO2, molten salts like alkali and alkaline earth sulfates, chlorides, and solid particles in the form of sand and fly ashes. Therefore, oxidation and hot corrosion are considered as two main destructive factors in TBCs. 

The P/T process will be coupled after an improved PUREX process that puts all technetimn, iodine, and neptunium into the waste fraction or into special fractions. Thus, the waste will contain fission products and minor actinides (americium and curium). The process will probably be a solvent extraction process although molten salt systems are also studied as an alternative. The main issue will be to obtain pure Am and Cm fractions for subsequent destruction, i.e., fractions that do not contain any lanthanides. Some of the lanthanides, which are chemically very similar to trivalent actinides, have very high neutron cross sections. Therefore, they must be removed to make actinide burning possible. In some cases, it may also be desirable to transmute some long-lived fission products, e.g., Tc and l, to more shortlived nuclides. 

Reports in this volume by Chimishkyan (p. 155) and by Wertejuk et al. (p. 91) describe methods for destruction of Adamsite developed in Russia and Poland, respectively. For arsenical agents of all types, other possibilities include oxidation of the arsenical agent with sodium hypochlorite (NaOCl) in aqueous medium, and oxidation by a mixture of molten salts that includes oxidants such a sodium nitrate and sodium peroxide. 

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