How is the hardness of the steam boiler feed water removed?

The hardness of the water used to feed steam boilers is easily eliminated through the use of decalcifiers with ion exchange resins which, when passed through by water containing dissolved calcium carbonate salts, capture the calcium ion carried by the water and yield the sodium ion stored by the resins.

As a result, the water coming out of the decalcifier is loaded with sodium carbonate salts.