Soda ash water treatment is introduction of soda ash to water systems to raise the pH of acidic water to near neutral. Soda ash is typically introduced to the water system by injection.
Soda ash, or sodium bicarbonate, removes chemicals that cause non-carbonate hardness. An insoluble precipitate that can be removed by filtration is formed. The advantage of soda ash over calcite and magnesia is that it does not add hardness to the water. Water treatment using soda ash is optimum at room temperature as sodium carbonate is sensitive to temperature.
Carbonate hardness is reduced by lime-soda ash treatment. Here, calcium (II) hydroxide is used together with the sodium bicarbonate. When calcium (II) hydroxide, or slake lime, is used together with soda ash, the minerals responsible for hardness form nearly insoluble precipitates. Calcium hardness is precipitated as calcium carbonate, while magnesium hardness is precipitated as magnesium hydroxide. The precipitates are then removed by processes such as filtration, sedimentation and coagulation.
Lime-soda ash is effective where a water supply has temporary hardness. This treatment, however, is not as effective where calcium and magnesium are primarily in sulfate or chloride compounds. Some hardness remains in water that has undergone lime-soda ash treatment as the precipitates formed are slightly soluble.