Cold Lime Process

Bicarbonate is removed by lime addition in accordance with the following reactions:

Ca(HCO3)2 + Ca(OH)2 ® 2 CaCO^ 2 H2O 8.3(1) Mg(HCO3)2 + 2 Ca(OH)2 ®

Mg(OH);,i+ 2 CaCO3t+ 2 H2O 8.3(2) 2 NaHCO3 + Ca(OH)2 ®

As indicated by reactions 8.3(1) and 8.3(2), alkalinity associated with hardness is removed by precipitation. However, sodium bicarbonate is converted to carbonate, which remains soluble and contributes to phenolphthalein alkalinity, as shown in 8.3(3).

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