Lime softening is a common way to to soften water. It involves the removal of impurities by chemical reaction with combinations of lime, soda ash (sodium carbonate) and caustic.
Calcium hardness precipitates as calcium carbonate and magnesium hardness as magnesium hydroxide. Bicarbonate alkalinity is first converted to carbonate form and is removed as calcium carbonate. Silica comes out as an insoluble silicon magnesium comples when it rexacts with magnesium hydroxide. Suspended solids, magnesium hydroxide and calcium carbonate sludge are removed by settling or filtration.
This process operates at ambient temperature and requires between 60 and 90 minutes retention time.