Recarbonation Of Softened Water

After the softening process, the pH is so high that reduction is necessary to prevent deposition of scales in distribution pipes. This can be accomplished inexpensively using carbon dioxide. We will therefore develop the method for determining the carbonic acid necessary to set the water to the equilibrium pH.

In recarbonation, the available calcium ion in solution is prevented from precipitation. Therefore, it remains to determine at what pH will the equilibrium condition be, given this calcium concentration. This determination is, in fact, the basis of the Langelier saturation pH. Adding carbonic acid will increase the acidity of the solution after it has neutralized any existing alkalinity.

Let the current pH be pHcur and the pH to which it is to be adjusted (the destination pH) be pHto. If pHcur is greater than pHto an acid is needed. No matter how insignificant, a natural water will always have an alkalinity in it. Alkalinities of surface water can vary from 10 to 800 mg/L (Sincero, 1968). Until it is all consumed, this alkalinity will resist the change in pH. Let the current total alkalinity be [Acur]geq in gram equivalents per liter. Let the total acidity to be added be [Acadd]geq in gram equivalents per liter.

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Responses

  • Terhi Viljanen
    Why is recarbonation necessary?
    2 months ago

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