Key Parameters and Kinetics of Oxidation of Lead (II) Solid Phases by Chlorine in Drinking Water

Equilibria and kinetics of transformations in the Pb(II)/Pb(IV)/chlorine system have a great impact on lead release in drinking water. To explore this system, oxidation of representative Pb(II) solid phases, predominantly hydrocerussite was carried out in chlorinated water with various alkalinities and pH values. It was determined that the oxidation of hydrocerussite by chlorine proceeded via three phases. These included a lag phase, a rapid transition phase and a final quasi steady-state phase. The lag phase corresponded to the transformation of hydrocerussite to cerussite PbCO3, while during the transition phase, the oxidation of PbCO3 and formation of -PbO2 occurred. Key water parameters, such as pH, chlorine concentration and dissolved inorganic carbonate concentration had a pronounced impact on the duration of the lag phase. Data of X-ray diffraction and scanning electron microscopy demonstrated that cerussite PbCO3 was formed as a transient phase during hydrocerussite oxidation, and dispersed microcrystals of scrutinyite -PbO2 were formed when chlorine was consumed.