The Release of Lead from the Reduction of Lead Oxide (PbO₂) by Natural Organic Matter

Abstract

PbO2 has been identified as an important scale in some distribution systems that historically use lead service lines and free chlorine for maintaining a disinfectant residual. The stability of this highly insoluble scale with respect to its reductive dissolution may play an important role in lead release into drinking water. In this study, we investigated the release of lead from a commercially available PbO2 in the presence of natural organic matter (NOM) using a hydrophobic acid extracted from the Iowa River. Experiments were conducted using synthetic solutions with different NOM concentrations, solution pH, and NOM samples with different levels of prechlorination. It was found that release of lead from PbO2 occurred both in solutions with and without NOM, and the extent of lead release increased with increasing NOM concentration and decreasing pH value. Furthermore, the released lead was Pb(II) and not particulate PbO2 conclusively showing that reductive dissolution occurred. Prechlorination of NOM reduced the rate of lead release. Our results indicate that PbO2 can be reduced both by water and NOM. Characterization of final solid phases by scanning electron microscopy and X-ray photoelectron spectroscopy are also presented.

Role of Pb(II) Defects in the Mechanism of Dissolution of Plattnerite (β-PbO2) in Water under Depleting Chlorine Conditions

“…and reductants naturally present in drinking water in DWDS, such as NOM and Br − , may be able to accelerate the reduction of this more stable PbO 2 phase and transform it into more soluble Pb(II) solids. 10,52,58 Although our experimental conditions are a simplification of actual field systems, our results clearly indicate the need for more research on the effects of decomposition of monochloramine and the presence of reductants such as NOM on the electronic structure of PbO 2 to clearly establish a mechanism for the dissolution of PbO 2 species under field drinking water conditions. …”

Crystal and morphological phase transformation of Pb(II) to Pb(IV) in chlorinated water☆

“…Historically, lead control in drinking water distribution systems has focused on Pb(II) mineralogy and solubility, and little attention has been given to Pb(IV). As a result, a number of recent research efforts have focused on Pb(II) to Pb(IV) transformation in drinking waters [9][10][11].…”

Kinetics of lead(IV) oxide (PbO2) reductive dissolution: Role of lead(II) adsorption and surface speciation

“…HOCl + OCl À ), a widely used disinfectant in distribution systems, provides a high ORP that favors PbO 2 formation [1,5,6]. The presence of reductants that include natural organic matter (NOM), Br À , I À , Mn 2+ , and Fe 2+ significantly enhanced the dissolution of PbO 2 [7][8][9][10][11][12][13]. The reductive dissolution of PbO 2 by water itself is even thermodynamically favorable [8,14].…”

“…The reductive dissolution of PbO 2 can be described by a coupled reduction and detachment process [13]. Based on the extremely low solubility of PbO 2 [30] and the instability of PbO 2 in water [8], essentially no dissolved Pb(IV) is expected to be present over the pH range of 2-9. Any dissolved lead will be Pb(II), and the dissolved lead concentration is therefore controlled by rate of reductive dissolution of PbO 2 rather than by a non-reductive dissolution process.…”