Formation of Lead(IV) Oxides from Lead(ll) Compounds

摘要

Lead(IV) oxide (PbO_2) is a corrosion product that can develop on lead pipes used for drinking water supply, and its stability can control lead concentrations in tap water. A set of batch experiments were performed to determine the extent of PbO_2 formation as a function of time, pH, the presence of dissolved inorganic carbon (DIC), and free chlorine concentration. Experiments were conducted with four lead(ll) compounds that are precursors of PbO_2 formation: dissolved lead(ll) chloride, massicot (β-PbO), cerussrte (PbCO_3), and hydrocerussite (Pb_3(OH)_2(CO_3)_2. While PbO_2 formed in the presence and absence of DIC, the presence of DIC accelerated PbO_2 formation and affected the identity of the PbO_2 (scrutinyite vs plattnerite) product For some conditions, intermediate solids formed that affected the identity of the PbO_2 produced. When no intermediate solids formed, hydrocerussite led to the formation of pure scrutinyite, and lead(ll) chloride and massicot led to mixtures of scrutinyite and plattnerite. Based on the experimental results, a conceptual model of lead(IV) oxide formation pathways was proposed.