The following balanced chemical equations represent the use of lime [Ca(OH)2] for softening of drinking water:
First step: lime added and all CO2 precipitates as CaCO3
Ca(OH)2 + CO2 à CaCO3 + H2O
Second step: more lime added and all Ca2+ and HCO3- precipitate as CaCO3
Ca(OH)2 + Ca2+ + 2HCO3- à 2CaCO3 + 2H2O
Third step: more lime added and Mg2+ and HCO3- are converted to MgCO3 which does not precipitate (also more CaCO3 precipitate is formed)
Mg2+ + HCO3- + Ca(OH)2 à CaCO3 + MgCO3 + 2H2O
Fourth step: more lime added reacts with the MgCO3 to form two precipitates, Mg(OH)2 and CaCO3
MgCO3 + Ca(OH)2 à CaCO3 + Mg(OH)2
Given the following concentrations of CO2 (8.5 mg/L), Ca2+ (48 mg/L), Mg2+ (39 mg/L), HCO3- (84 mg/L), and flow rate (1 MGD), determine the following:
a) the required lime [Ca(OH)2], lb/day
b) the total mass of precipitate (sludge) formed, lb/day
c) the total amount of water formed, gal/day
d) the residual concentrations of CO2, Ca2+, and Mg2+ (mg/L).
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The following balanced chemical equations represent the use of lime [Ca(OH)2] for softening of drinking water:...