Solvay Process - Byproducts and Wastes

Byproducts and Wastes

The principal byproduct of the Solvay process is calcium chloride (CaCl₂) in aqueous solution. The process has other waste and byproducts as well. Not all of the limestone that is calcined is converted to quicklime and carbon dioxide (in reaction II); the residual calcium carbonate and other components of the limestone become wastes. In addition, the salt brine used by the process is usually purified to remove magnesium and calcium ions, typically to form carbonates; otherwise, these impurities would lead to scale in the various reaction vessels and towers. These carbonates are additional waste products.

In inland plants, such as that in Solvay, New York, the byproducts have been deposited in "waste beds"; the weight of material deposited in these waste beds exceeded that of the soda ash produced by about 50%. These waste beds have led to water pollution, principally by calcium and chloride. The waste beds in Solvay, New York substantially increased the salinity in nearby Onondaga Lake, which is among the most polluted lakes in the U.S. and is a superfund pollution site. As such waste beds age, they do begin to support plant communities which have been the subject of several scientific studies.

At seaside locations, such as those at Saurashtra, Gujarat, India, the CaCl₂ solution may be discharged directly into the sea, apparently without substantial environmental harm. At Osborne, South Australia, a settling pond is now used to remove 99% of the CaCl₂ as the former discharge was silting up the shipping channel.