Sodium carbonate bath, molten

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. 

SALT BATH. A molten mixture of sodium, potassium, barium, and calcium chlorides or nitrates to which sodium carbonate and sodium cyanide are sometimes added. Used for hardening and temperature of metals and fox annealing both feuous and nonfeiious metals, Tempeiatuies used may be as high as 1,315°C for hardening high-speed steels. Commercial mixtures are available for a variety of specifications. 

Eight grams of iron powder, 45 g. of flowers of sulfur, 40 g. of potassium carbonate, and 8 g. of anhydrous sodium carbonate are very thoroughly mixed and put into a covered clay crucible. This mixture is then heated for a period of 1 to 1-J hours at 900°, at which temperature the reaction mixture is molten. On the completion of the reaction the crucible is allowed to come to room temperature and is then submerged in a beaker of water and the reacted mixture digested on a water bath. The supernatant liquid becomes dark green [the iron complex NasFeS(OH)3]3 it is then... 

In molten bath processes, crushed coal is passed with reacting gases into the liquid bath, where gasification occurs. The ash can become part of the liquid bath or can be separated. The media include liquid iron and liquid sodium carbonate. 

Molten salt oxidation Combines chemical and thermal treatment. Wastes and oxygen are fed into a bath of molten caustic salt—usually sodium carbonate or a mixture of sodium and potassium carbonate. The wastes are oxidized, typically producing emissions of carbon dioxide, water, nitrogen, and oxygen ash and soot are retained in the melt. Salt can later be removed for disposal or for processing and recycling. 

Low-carbon steel is heated at 870°C in a molten 30% sodium cyanide bath for about one hour. Quenching in oil or water from this bath hardens the surface of the steel... 

The organic product is destroyed by a bath of molten salt (sodium carbonate alone or a mixture with potassium carbonate). The bath is stable, cheap, with no vapour pressure, non toxic and recyclable. The reactor temperature is between 800 and 1000°C. Recycling enables any unreacted salt to be reused. After dissolving and filtering of the carbonate solution, the addition of CO2 enables a re-precipitation of the sodium bicarbonate. 

In 1807 Sir Humphry Davy (1778-1829) devised an electrolysis apparatus that used electrodes immersed in a bath of melted sodium hydroxide. When he passed an electric current through the system, metallic sodium formed at the negative (cathode) electrode. He first performed this experiment with molten potassium carbonate to liberate the metal potassium, and he soon followed up with the sodium experiment. Today, sodium and some of the other alkali metals are still produced by electrolysis. The types of electrolytes may vary using a mixture of sodium chloride and calcium chloride and then further purifying the sodium metal. 

The electrolysis Of fused alkali salts.—Many attempts have been made to prepare sodium directly by the electrolysis of the fused chloride, since that salt is by far the most abundant and the cheapest source of the metal. The high fusion temp. the strongly corrosive action of the molten chloride and the difficulty of separating the anodic and cathodic products, are the main difficulties which have been encountered in the production of sodium by the electrolysis of fused sodium chloride. Attention has been previously directed to C. E. Acker s process for the preparation of sodium, or rather a sodium-lead alloy, by the electrolysis of fused sodium chloride whereby sodium is produced at one electrode, and chlorine at the other but the process does not appear to have been commercially successful. In E. A. Ashcroft s abandoned process the fused chloride is electrolyzed in a double cell with a carbon anode, and a molten lead cathode. The molten lead-sodium alloy was transported to a second chamber, where it was made the anode in a bath of molten sodium hydroxide whereby sodium was deposited at the cathode. A. Matthiessen 12 electrolyzed a mixture of sodium chloride with half its weight of calcium chloride the addition of the chloride of the alkaline earth, said L. Grabau, hinders the formation of a subchloride. J. Stoerck recommended the addition of... 

The raw materials are blended and charged into the glass furnace, which is a refractory lined bath covered by a refractory roof. The furnace is heated to about 2000 °C by burners in the space above the molten glass. As the raw materials enter the bath, the carbonates decompose and evolve carbon dioxide, which helps to agitate the bath and to disperse the solids in the melt. The solids react to produce the sodium/calcium/magnesium silicate which is the principle constituent of most glasses. 

Case hardening of steel using a sodium cyanide molten bath depends on the above reactions where the active carbon and nitrogen are absorbed into the steel surface. Sodium cyanide is a good reducing agent and the oxides of tin, lead, copper, or manganese are readily reduced (Kirk-Othmer, 1993). 

For high-temperature operations, materials, and fuels are key technologies. There is a century of large-scale experience in the use of fluoride molten salts. Aluminum is made by electrolysis of a mixture of bauxite and sodium aluminum fluoride salts at 1000 C in large graphite baths. Fluoride salts are compatible with graphite fuels. A smaller nuclear experience base exists with molten fluoride salts in molten salt reactors. Nickel alloys such as modified Hastelloy-N have been qualified for service to 750 C. A number of metals and carbon-carbon composites have been identified for use at much higher temperatures however, these materials have not yet been fully developed or tested for such applications. 

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