chapter  2
12 Pages

Cold Process Lime-Soda Softening

A fundamental knowledge of the chemical softening process is paramount in understanding the basic principles of ion exchange.

Hardness (any material that forms a precipitate with the sodium salt of fatty acids) is classified as either permanent or temporary. The only chemical com­ pound that forms temporary hardness is calcium bicarbonate [Ca(HC03)2], which depends on the presence of dissolved carbon dioxide in the water to even exist. In the absence of carbon dioxide, calcium bicarbonate reverts to calcium carbonate. {Note: Calcium bicarbonate does not exist in the dry form.) All other hardness is permanent.