Study of Soda Ash uses and process involved....
The most important use for sodium carbonate is in the manufacture of glass. When heated to very high temperatures, combined with sand (SiO2) and calcium carbonate (CaCO3), and cooled very rapidly, glass is produced.
Sodium carbonate is also used as a relatively strong base in various settings. For example, sodium carbonate is used as a pH regulator to maintain stable alkaline conditions necessary for the action of the majority of developing agents.[citation needed] It is a common additive in municipal pools used to neutralize the acidic effects of chlorine and raise pH. In cooking, it is sometimes used in place of sodium hydroxide for lying, especially with German pretzels and lye rolls. These dishes are treated with a solution of an alkaline substance in order to change the pH of the surface of the food and thus improve browning.
In chemistry, it is often used as an electrolyte. This is because electrolytes are usually salt-based, and sodium carbonate acts as a very good conductor in the process of electrolysis. Additionally, unlike chloride ions which form chlorine gas, carbonate ions are not corrosive to the anodes. It is also used as a primary standard for acid-base titrations because it is solid and air-stable, making it easy to weigh accurately.
In domestic use, it is used as a water softener during laundry. It competes with the ions magnesium and calcium in hard water and prevents them from bonding with the detergent being used. Without using washing soda, additional detergent is needed to soak up the magnesium and calcium ions. Called Washing Soda or Sal Soda in the detergent section of stores, it effectively removes oil, grease, and alcohol stains. Sodium carbonate is also used as a descaling agent in boilers such as found in coffee pots, espresso machines, etc.[citation needed]
In dyeing with fiber-reactive dyes, sodium carbonate (often under a name such as soda ash fixative or soda ash activator) is used to ensure proper chemical bonding of the dye with the fibers, typically before dyeing (for tie dyes), mixed with the dye (for dye painting), or after dyeing (for immersion dyeing)
Other Applications
Sodium carbonate is a food additive (E500) used as an acidity regulator, anticaking agent, raising agent and stabilizer. It is one of the components of kansui, a solution of alkaline salts used to give ramen noodles their characteristic flavor and texture
Sodium carbonate is also used in the production of sherbet lollies. The cooling and fizzing sensation results from the endothermic reaction between sodium carbonate and a weak acid, commonly citric acid, releasing carbon dioxide gas, which occurs when the sherbet is moistened by saliva.
Sodium carbonate is used by the brick industry as a wetting agent to reduce the amount of water needed to extrude the clay
In casting, it is referred to as "bonding agent" and is used to allow wet alginate to adhere to gelled alginate.
Sodium carbonate is used in toothpastes, where it acts as a foaming agent, an abrasive, and to temporarily increase mouth pH.
Sodium carbonate may be used for safely cleaning silver. First, aluminium foil is added to a glass or ceramic container, and covered with very hot water and some sodium carbonate.
Occurrence
Sodium carbonate is soluble in water, but can occur naturally in arid regions, especially in the mineral deposits (evaporites) formed when seasonal lakes evaporate. Deposits of the mineral natron, natural sodium carbonate decahydrate, have been mined from dry lake bottoms in Egypt since ancient times, when natron was used in the preparation of mummies and in the early manufacture of glass. Sodium carbonate has three known forms of hydrates: sodium carbonate decahydrate (natron), sodium carbonate heptahydrate (not known in mineral form) and sodium carbonate monohydrate (mineral thermonatrite). The anhydrous mineral form of sodium carbonate is quite rare and called natrite. Sodium carbonate also erupts from Tanzania's unique volcano Ol Doinyo Lengai, and probably erupted from other volcanoes in the past . All three mineralogical forms of sodium carbonate, as well as sodium carbonate bicarbonate, trona, are also known from ultra-alkaline pegmatitic rocks, i.e. from the Kola Peninsula.
Production
Mining
Trona, hydrated sodium bicarbonate carbonate (Na3HCO3CO3·2H2O), is mined in several areas of the United States and provides nearly all the domestic sodium carbonate. Large natural deposits found in 1938, such as the one near Green River, Wyoming, have made mining more economical than industrial production in North America.
It is also mined out of certain alkaline lakes such as Lake Magadi in Kenya by using a basic dredging process and it is also self-regenerating so will never run out in its natural source.
Solvay method
The Solvay process produces soda ash (predominantly sodium carbonate (Na2CO3)) from brine (as a source of sodium chloride (NaCl)) and from limestone (as a source of calcium carbonate (CaCO3)).
The overall process is:
2 NaCl + CaCO3 → Na2CO3 + CaCl2
The actual implementation of this global, overall reaction is intricate. A simplified description can be given using the four different, interacting chemical reactions illustrated in the figure. In the first step in the process, carbon dioxide (CO2) passes through a concentrated aqueous solution of sodium chloride (NaCl) and ammonia (NH3).
NaCl + CO2 + NH3 + H2O → NaHCO3 + NH4Cl (I)
In industrial practice, the reaction is carried out by passing concentrated brine through two towers. In the first, ammonia bubbles up through the brine and is absorbed by it. In the second, carbon dioxide bubbles up through the ammoniated brine, and sodium bicarbonate (NaHCO3) precipitates out of the solution. Note that, in a basic solution, NaHCO3 is less water-soluble than sodium chloride. The ammonia (NH3) buffers the solution at a basic pH; without the ammonia, a hydrochloric acid byproduct would render the solution acidic, and arrest the precipitation.
The necessary ammonia "catalyst" for reaction (I) is reclaimed in a later step, and relatively little ammonia is consumed. The carbon dioxide required for reaction (I) is produced by heating ("calcination") of the limestone at 950 - 1100 °C. The calcium carbonate (CaCO3) in the limestone is partially converted to quicklime (calcium oxide (CaO)) and carbon dioxide:
CaCO3 → CO2 + CaO (II)
The sodium bicarbonate (NaHCO3) that precipitates out in reaction (I) is filtered out from the hot ammonium chloride (NH4Cl) solution, and the solution is then reacted with the quicklime (calcium oxide (CaO)) left over from heating the limestone in step (II).
2 NH4Cl + CaO → 2 NH3 + CaCl2 + H2O (III)
CaO makes a strong basic solution. The ammonia from reaction (III) is recycled back to the initial brine solution of reaction (I).
The sodium bicarbonate (NaHCO3) precipitate from reaction (I) is then converted to the final product, sodium carbonate (Na2CO3), by calcination (160 - 230 C), producing water and carbon dioxide as byproducts:
2 NaHCO3 → Na2CO3 + H2O + CO2 (IV)
The carbon dioxide from step (IV) is recovered for re-use in step (I). When properly designed and operated, a Solvay plant can reclaim almost all its ammonia, and consumes only small amounts of additional ammonia to make up for losses. The only major inputs to the Solvay process are salt, limestone and thermal energy, and its only major byproduct is calcium chloride, which is sold as road salt.
Additional details of the industrial implementation of this process are available in the report prepared for the European Soda Ash Producer's Association.
