Washington University in St. Louis Washington University Open Scholarship All Theses and Dissertations (ETDs) January 2010 Dissolution, Formation, and Transformation of the Lead Corrosion Product PbO2: Rates and Mechanisms of Reactions that Control Lead Release in Drinking Water Distribution Systems Yanjiao Xie Washington University in St. Louis Follow this and additional works at: https://openscholarship.wustl.edu/etd Recommended Citation Xie, Yanjiao, "Dissolution, Formation, and Transformation of the Lead Corrosion Product PbO2: Rates and Mechanisms of Reactions that Control Lead Release in Drinking Water Distribution Systems" (2010). All Theses and Dissertations (ETDs). 387. https://openscholarship.wustl.edu/etd/387 This Dissertation is brought to you for free and open access by Washington University Open Scholarship. It has been accepted for inclusion in All Theses and Dissertations (ETDs) by an authorized administrator of Washington University Open Scholarship. For more information, please contact [email protected]. WASHINGTON UNIVERSITY IN ST. LOUIS School of Engineering and Applied Science Department of Energy, Environmental and Chemical Engineering Dissertation Examination Committee: Daniel E. Giammar, Chair William E. Buhro Young-Shin Jun Cynthia S. Lo Jill D. Pasteris Jay R. Turner DISSOLUTION, FORMATION, AND TRANSFORMATION OF THE LEAD CORROSION PRODUCT PbO2 : RATES AND MECHANISMS OF REACTIONS THAT CONTROL LEAD RELEASE IN DRINKING WATER DISTRIBUTION SYSTEMS by Yanjiao Xie A dissertation presented to the Graduate School of Arts and Sciences of Washington University in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Energy, Environmental and Chemical Engineering August 2010 Saint Louis, Missouri ABSTRACT OF THE DISSERTATION Dissolution, Formation, and Transformation of the Lead Corrosion Product PbO2: Rates and Mechanisms of Reactions that Control Lead Release in Drinking Water Distribution Systems by Yanjiao Xie Doctor of Philosophy in Energy, Environmental & Chemical Engineering Washington University in St. Louis, 2010 Research Advisor: Professor Daniel Giammar, Chair As one of the major lead corrosion products in lead service lines, lead(IV) oxide (PbO2) can react with water through reductive dissolution, resulting in elevated lead concentrations in tap water. Limited data are available on the rates and mechanisms of PbO2 dissolution. Information regarding the impact of water chemistry on the rates and mechanisms of PbO2 dissolution can provide potential strategies to control the release of lead from corrosion products to drinking water. The present study investigated effects of water chemistry on the rates and mechanisms of PbO2 dissolution, the equilibrium solubility of PbO2, and the rates of lead release from lead pipes with corrosion scales. The dissolution rate of pure plattnerite (β-PbO2) was investigated as a function of pH and the concentrations of carbonate, orthophosphate, free chlorine, and monochloramine in continuously stirred tank reactors (CSTR). Complementary batch ii experiments were conducted to compare the effects of water chemistry on the PbO2 dissolution rate for different solid-water contact times. The equilibrium solubility of plattnerite in the presence of free chlorine was then investigated. Lead release from pipe scales was determined under different water chemistry conditions at flow or no-flow conditions to optimize the water chemistry for mitigating lead release. For these experiments new lead pipes were conditioned in the presence of free chlorine and carbonate to form corrosion scales. Dissolution experiments provided direct evidence that the PbO2 dissolution rate increases when the disinfectant is switched from free chlorine to monochloramine, which is consistent with the high lead concentrations observed in Washington D.C. from 2001 to 2004 following such a switch. Lower pH and the presence of carbonate accelerated PbO2 dissolution. Addition of orthophosphate as a potential corrosion inhibitor had multiple effects on PbO2 dissolution rates. A detailed mechanism and rate model were proposed for PbO2 reductive dissolution. Batch experiments showed that the residence time also played an important role in controlling dissolved lead concentrations. Pipe scales developed under drinking water conditions contained PbO2 and hydrocerussite (Pb3(CO3)2(OH)2). In experiments with these pipe scales, when compared with stagnant conditions water flow significantly accelerated the release of both dissolved and total lead from pipe scales. Among various water chemistry conditions, the dissolved lead was lowest from corrosion scales in contact with solutions containing orthophosphate. Two models were proposed to predict lead release from pipe scales. iii Acknowledgement I would like to express my greatest appreciation to my advisor, Dr. Daniel Giammar, for his constant hands-on guidance, assistance, and support throughout my PhD research. I am so fortunate to have such a knowledgeable, dedicated, nice, and open-minded advisor, who helped me overcome the difficulties and complete this research with satisfactory results. I would also like to thank my committee members, Dr. William Buhro, Dr. Young-Shin Jun, Dr. Cynthia Lo, Dr. Jill Pasteris and Dr. Jay Turner, for giving their valuable time and constructive suggestions to this study through different stages of my research. I sincerely thank Yin Wang and Vidhi Singhal for their contributions to some PbO2 dissolution experiments, and Tyler Nading for his contribution to the pipe lead release experiments. I also want to thank Abhas Singh, Yun Luo, and Professor Jeff Catalano for analyzing pipe scale samples using X-ray adsorption near-edge spectroscopy. I want to thank Yi Yang for assisting me in developing the model for lead release from pipe scales. Special thanks are extended to James Noel, Kate Nelson, and other fellow ACL members who provided valuable suggestions to this study. I am very grateful for the research funding from Water Research Foundation (WRF) and my fellowship support from the McDonnell International Scholars Academy at Washington University. I want to thank the director of the McDonnell Academy, Dr. James Wertsch, for admitting me to this great leadership program and exposing me to iv American politics, economy, culture, and society through various events. It is the McDonnell Academy and ACL members that have made my PhD life colorful and enjoyable. Yanjiao Xie Washington University in St. Louis August 2010 v Table of Contents Abstract ............................................................................................................................ ii Acknowledgement .......................................................................................................... iv List of Tables .................................................................................................................. ix List of Figures .................................................................................................................. x Chapter 1. Introduction and overview ......................................................................... 1 1.1. Introduction ......................................................................................................... 1 1.1.1 Lead Corrosion and Regulation in Water Distribution Systems1 1.1.2 Lead Corrosion Products ............................................................ 2 1.1.3 Electrochemistry of the Pb(0)/Pb(II)/Pb(IV) System ................. 3 1.1.4 Equilibrium Solubility of Lead Corrosion Products .................. 6 1.1.5 Dissolution Rates of Lead Corrosion Products .......................... 9 1.1.6 Lead Release from Pipe Scales .................................................. 9 1.1.7 Mitigating Lead Release ........................................................... 10 1.2 Research Objectives ......................................................................................... 12 1.3 Overview of Dissertation ................................................................................. 12 References: ................................................................................................................ 14 Chapter 2. Effects of pH and carbonate concentration on dissolution rates of the lead corrosion product PbO2........................................................................................ 17 Abstract ..................................................................................................................... 18 2.1. Introduction ...................................................................................................... 19 2.2. Materials and Methods ..................................................................................... 20 2.2.1 Materials ................................................................................... 20 2.2.2. Analytical Methods ................................................................. 21 2.2.3. Measurement of Dissolution Rates ......................................... 21 2.2 Results and Discussion .................................................................................... 25 2.2.1 Plattnerite Dissolution Rates .................................................... 25 2.2.2. Effect of pH and DIC on Plattnerite Dissolution ....................... 28 2.2.3 Dissolution During Initial Period of Reactor Operation .......... 31 2.2.4. Equilibrium Versus Kinetic Control of Dissolved Lead Concentrations ....................................................................................