Solvay process
The worldwide production of soda ash in 2005 was estimated at 42 million tonnes,[2] which is more than six kilograms (13 lb) per year for each person on Earth.
By the late 18th century these sources were insufficient to meet Europe's burgeoning demand for alkali for soap, textile, and glass industries.
[7] In 1791, the French physician Nicolas Leblanc developed a method to manufacture soda ash using salt, limestone, sulfuric acid, and coal.
Although the Leblanc process came to dominate alkali production in the early 19th century, the expense of its inputs and its polluting byproducts (including hydrogen chloride gas) made it apparent that it was far from an ideal solution.
[7][8] It has been reported that in 1811 French physicist Augustin Jean Fresnel discovered that sodium bicarbonate precipitates when carbon dioxide is bubbled through ammonia-containing brines – which is the chemical reaction central to the Solvay process.
As has been noted by Desmond Reilly, "The story of the evolution of the ammonium–soda process is an interesting example of the way in which a discovery can be made and then laid aside and not applied for a considerable time afterwards.
"[9] Serious consideration of this reaction as the basis of an industrial process dates from the British patent issued in 1834 to H. G. Dyar and J. Hemming.
In 1861, Belgian industrial chemist Ernest Solvay turned his attention to the problem; he was apparently largely unaware of the extensive earlier work.
By 1864 Solvay and his brother Alfred had acquired financial backing and constructed a plant in Couillet, today a suburb of the Belgian town of Charleroi.
In 1938 large deposits of the mineral trona were discovered near the Green River in Wyoming from which sodium carbonate can be extracted more cheaply than produced by the process.
In the first step in the process, carbon dioxide (CO2) passes through a concentrated aqueous solution of sodium chloride (table salt, NaCl) and ammonia (NH3).
In the second, carbon dioxide bubbles up through the ammoniated brine, and sodium bicarbonate (baking soda) precipitates out of the solution.
Additional details of the industrial implementation of this process are available in the report prepared for the European Soda Ash Producer's Association.
In addition, the salt brine used by the process is usually purified to remove magnesium and calcium ions, typically to form carbonates (MgCO3, CaCO3); otherwise, these impurities would lead to scale in the various reaction vessels and towers.
[15][16] At seaside locations, such as those at Saurashtra, Gujarat, India,[17] the CaCl2 solution may be discharged directly into the sea, apparently without substantial environmental harm (although small amounts of heavy metals in it may be a problem), the major concern is discharge location falls within the Marine National Park of Gulf of Kutch which serves as habitat for coral reefs, seagrass and seaweed community.
A report published in 1999 by the United Nations Environment Programme (UNEP), listed Spiagge Bianche among the priority pollution hot spots in the coastal areas of the Mediterranean Sea.
