Molten caustic soda

Refining. The alloy of bismuth and lead from the separation procedures is treated with molten caustic soda to remove traces of such acidic elements as arsenic and teUutium (4). It is then subjected to the Parkes desilverization process to remove the silver and gold present. This process is also used to remove these elements from lead. 

The spectacular success (in 1807) of Humphry Davy, then aged 29 y, in isolating metallic potassium by electrolysis of molten caustic potash (KOH) is too well known to need repeating in detail." Globules of molten sodium were similarly prepared by him a few days later from molten caustic soda. Earlier experiments with aqueous solutions had been unsuccessful because of the great reactivity of these new elements. The names chosen by Davy reflect the sources of the elements. 

Other methods of cleaning iron and steel include immersion in molten sodium hydride and cathodic treatment in molten caustic soda. These methods may be hazardous to personnel, and should not be carried out by the uninitiated, or without professional supervision. 

The Alcoa (Aluminum Company of America) process involves the electrolysis of aluminum chloride which is carried out in a molten bath of the composition 50% sodium chloride, 45% lithium chloride and 5% aluminum chloride, maintained at 700 °C. The Bayer process, which involves the production of pure alumina by the dissolution of bauxite with caustic soda and which has been described in the chapter on hydrometallurgy, must be taken into account while presenting a complete picture of the aluminum extraction flowsheet. It... 

Sir Humphry Davy (1778-1829) isolated the element by electrolysis of molten caustic soda (NaOH). 

Tungsten metal is not affected by aqueous alkalies at room temperature. In molten state, caustic soda and caustic potash slowly oxidize tungsten in the presence of air. Oxidiation is more rapid in the presence of an oxidizing agent such as potassium nitrate, potassium chlorate, or lead dioxide. A similar reaction occurs with fused sodium or potassium carbonate. Tungsten dissolves... 

When an electrolyte which is without action on vanadium at ordinary temperatures (for example, dilute solutions of mineral acids, of oxalic acid, or of potassium halides) is electrolysed with a vanadium anode, a complex tetravalent vanadium ion is produced. Similarly, electrolysis at 100° C. and in molten chlorides of sodium or zinc gives rise to complex tetravalent vanadium ions. The E.M.F. in each case is found to be independent of the nature of the electrolyte. When, however, solutions of caustic soda or of caustic potash are employed, the vanadium dissolves as a pentavalent ion, irrespective of variations... 

Molten salts or ionic liquids (also referred to as fused salts by some authors) were among the very first media to be employed for electrochemistry. In fact, Sir Humphrey Davy describes electrochemical experiments with molten caustic potash (KOH) and caustic soda (NaOH) [1] as early as 1802 A wide variety of single molten salts and molten salt mixtures have been used as solvents for electroanalytical chemistry. These melts run the gamut from those that are liquid well below room temperature to those melting at more than 2000°C. The former present relatively few experimental challenges, whereas the latter can present enormous difficulties. For example, commercially available Teflon- and Kel-F-shrouded disk electrodes and Pyrex glass cells may be perfectly adequate for electrochemical measurements in ambient temperature melts such as the room-temperature chloroaluminates, but completely inadequate for use with molten sodium fluoroaluminate or cryolite (mp = 1010°C), which is the primary solvent used in the Hall-Heroult process for aluminum electrowinning. 

The improper gasket may have been installed months or perhaps years before. Typically this gasket is exposed to a high vacuum and caustic soda vapors. Unrelated problems within the unit that day created a high liquid level in the vessel that exposed the gasket to atmospheric pressures and molten-liquid 98-percent caustic soda. 

Figure 6-6 Molten caustic soda leaks from above due to an improper gasket.

Although compounds of sodium and potassium were known in ancient times, it was not until Humphrey Davy s famous electrolytic experiments in 1807 on molten caustic soda and potash that the metals themselves were first isolated. Lithium was first recognized as an alkali metal in various silicate and mica minerals in 1817 (by ArfVedson, who thus named it from the Greek word for stone) and first isolated, again by Davy, in 1818. The discovery of cesium (1860) and rubidium (1861) had to await the development of atomic spectroscopy (by Bunsen and Kirchoff) their names reflect the colors of their dominant spectral lines (Latin caesius, sky blue, and rubidus, deep-red). 

Draw the saturated-liquid line (1 atm isobar) on an enthalpy concentration chart for caustic soda solutions. Show the 200°F, 250°F, 300 F, 350°F, and 4CX)°F isotherms in the liquid region, and draw tie lines for these temperatures to the vapor region. Using the data from National Bureau of Standards Circular 500, show where molten NaOH would be on this chart. Take the remaining data from the following table and the steam tables. 

Properties White powder. D 2.27, sublimes at 1275C. Soluble in molten caustic soda or potash converted to sodium hydroxide by water. 

The overall cell reaction produces gaseous H2 and CI2 and an aqueous solution of NaOH, called caustic soda. Solid NaOH is then obtained by evaporation of the residual solution. This is the most important commercial preparation of each of these substances. It is much less expensive than the electrolysis of molten NaCl, because it is not necessary to heat the solution. 

For caustic fusion of the sulfonic acids salts it has been observed that if para-isomer is predominant (for producing para-cresol) the viscosity of the molten mass is too high and it poses problems during agitation of the mass. It has been found that 4-5% of caustic potash (KOH) if added to caustic soda, maintains proper fiuidity throughout the reaction. 

In Atul s process of production of para-cresol, toluene is sulfonated with 98-102% H2SO4 to produce a mixture of isomeric toluene sulfonic acids. The acid mixture is neutralized with CaC03/Na2C03 and then fused with caustic soda lye (70% NaOH) with 3-5% KOH to maintain the fluidity of the molten mass. By heating the mixture around 330°C for... 

Sodium was the next alkali metal to be discovered after potassium. Sir Humphrey Davy isolated sodium in 1807 (around the same time he identified potassium) by running an electric current through molten caustic soda, or soda ash, to produce sodium hydroxide. 

Sodium is a soft, silvery alkali metal and reacts vigorously with water to generate hydrogen gas. The word sodium is derived from sodanum (a Medieval Latin name for a headache remedy), and natrium (Latin for soda ) is the origin of the element s symbol. Humphry Davy isolated the element in 1807 via the electrolysis of caustic soda, NaOH. Currently, sodium metal is obtained from the electrolysis of a molten mixture of sodium chloride and... 

A commercial digestion process is currently in use for the extraction of REE, including yttrium from monazite. The process is based on the application of caustic soda, and one of the products is REE hydroxide. The rare earths are leached from bastnaesite with hydrochloric acid (or sulfuric acid), followed by calcination at >600°C they are then treated with 16 M nitric acid (Kirk-Othmer 1999). Yttrium is produced as pure silver metal, both on the laboratory and industrial scale, by molten salt electrolysis and metallothermic reduction of the fluoride, oxide, or chloride with calcium following an enrichment process, after separation by fractionated crystallization, ion exchange... 

---