A drinking water treatment plant wants to compare the efficacy of three different solid coagulants, Alum [Al(OH)3(s)], Lime (CaCO3(s)), and Ferric Chloride (FeCl3(s)), for removing the phosphate (PO43-) level to 1 mg/L. The following are the equilibrium reactions [and the respective equilibrium constants (or solubility products, Ksp)] that result in phosphate removalfor each solid, the second reaction being more relevant in each case: Alum: Al(OH)3(s) ↔ Al3+ + 3OH- AlPO4(s) ↔ Al3+ + PO43- Ksp = 9.84 x 10-21 Lime: CaCO3(s) ↔ Ca2+ + CO32- Ca3(PO4)2(s) ↔ Ca2+ + PO43- Ksp = 1 x10-27 Ferric Chloride: FeCl3 (s) ↔ Fe3+ + 3Cl- Fe(PO4)(s) ↔ Fe3+ + PO43- Ksp = 1x10-26.4 What concentrations of Fe 3+, Al3+, and Ca2+ will be needed to maintain a phosphate concentration of 1 mg/L? What would be the best choice of solid coagulant for the Drinking Water Treatment Plant? Assume the prices of different coagulants are the same.
A drinking water treatment plant wants to compare the efficacy of three different solid coagulants, Alum [Al(OH)3(s)], Lime (CaCO3(s)), and Ferric Chloride (FeCl3(s)), for removing the phosphate (PO43-) level to 1 mg/L. The following are the equilibrium reactions [and the respective equilibrium constants (or solubility products, Ksp)] that result in phosphate removal
for each solid, the second reaction being more relevant in each case:
Alum: Al(OH)3(s) ↔ Al3+ + 3OH-
AlPO4(s) ↔ Al3+ + PO43- Ksp = 9.84 x 10-21
Lime: CaCO3(s) ↔ Ca2+ + CO32-
Ca3(PO4)2(s) ↔ Ca2+ + PO43- Ksp = 1 x10-27
Ferric Chloride: FeCl3 (s) ↔ Fe3+ + 3Cl-
Fe(PO4)(s) ↔ Fe3+ + PO43- Ksp = 1x10-26.4
What concentrations of Fe 3+, Al3+, and Ca2+ will be needed to maintain a phosphate concentration of 1 mg/L? What would be the best choice of solid coagulant for the Drinking Water Treatment Plant? Assume the prices of different coagulants are the same.
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