Abstract
Lead dioxide (PbO2) is a new form of lead corrosion product discovered in the drinking water distribution systems. It is formed via the chlorination of lead-containing plumbing materials. In this study, we investigated the adsorption of free chlorine (HOCl/OCl−) on PbO2 to explore the loss of free chlorine in the bulk solution and the reactivity of adsorbed free chlorine in the presence of PbO2. Our results indicated that adsorption reached equilibrium in approximately 6 h and ionic strength did not significantly affect adsorption. Langmuir adsorption isotherm provided good fittings of the experimental data. Maximum adsorption capacity of PbO2 was dependent on the solution pH value, with the maximum occurring at pH 8, which can be explained by electrostatic interactions between free chlorine and PbO2 surfaces. Both carbonate and phosphate buffers inhibited free chlorine adsorption, and phosphate was a stronger inhibitor. Adsorbed free chlorine was found to maintain its oxidation ability. Our results indicated that the presence of PbO2 may induce a loss of free chlorine in the bulk solution because of adsorption. Nevertheless, adsorbed free chlorine remains active and may exhibit disinfection capability. This is the first study to show that free chlorine can act as an “adsorbate” in the distribution system and this reaction should be considered in the redox transformation of corrosion products.
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