non-carbonate hardness

Non-carbonate hardness is caused by the association of the hardnesscausing cations with sulphates, chlorides and nitrates.

The lime-soda ash purification process may contribute significant quantities of sodium if a large concentration of non-carbonate hardness must be removed.

Lime is added, usually in a calculated excess, precipitating most of the calcium carbonate and magnesium hydroxide; this is followed by soda ash addition to remove the excess lime and any non-carbonate hardness.