Geochemical Thermodynamics of Lead Removal from Water with Limestone

Limestone-based material can reduce concentrations of lead below 0.001 mg/L in water during metals-removal tests with field and laboratory samples, resulting in > 99% removal efficiency. Thermodynamic constraints appear to be favorable for reactions involving the formation of cerussite and hydrocerussite during lead removal with untreated limestone. Thermodynamic values for these reactions show strongly negative Gibbs free energy changes and yield a theoretical removal limit of about 0.001 mg/L or less for lead, demonstrating reasonable agreement with tests on laboratory and field samples. The solubility product of hydrocerussite is about 10 −47 , indicating the waste product of lead removal with limestone is likely to be stable at neutral to basic pH values.