AWWA WQTC71525

This project focuses on the dissolution and transformation rates of lead carbonatecorrosion products. Hydrocerussite, Pb₃(CO₃)₂(OH)₂, is a widely observed lead corrosion product, and its dissolution in response to changes in water chemistry can greatly affect the dissolved lead concentration in water distribution systems. The dissolution rate of hydrocerussite was investigated as a function of pH and the concentrations of dissolvedinorganic carbon, orthophosphate, and chloramine. The rates and rate constants of synthetic hydrocerussite dissolution were measured as a function of water chemistry using completely-mixed continuous-flow reactors. Lead release rates from lead service lines that had been used in waterdistribution for 80-100 years were investigated as a function of water chemistry, recirculation flow rates, and stagnation times. The lead pipe scale was also characterized for molecular structure, morphology, and mineralogy before and after each experiment. The experimentally measured dissolution rates were used to generate a model for lead release rates as a function of water chemistry and then compared to the lead release rate from lead pipe extracted from a water distribution system. Such a model will allow water treatment facilities to determine lead concentrations as a function of measurable bulk water properties. Utilities are implementing lead corrosion control strategies, such as the addition of phosphate, to control lead concentrations in their distribution systems. Thetransformation of hydrocerussite to lower solubility lead phosphates was monitored in real-time using Raman spectroscopy. The data was then used to develop conceptual models for the specific processes governing the transformation of hydrocerussite to lead phosphates. A numerical solution to the system of equations will then be used to simulate the transformation process with time. The data were evaluated to determine whether the transformation occurs via dissolution of one phase and subsequentprecipitation of the second phase, or by direct transformation of the solid. Models for each approach were tested and provide insight into the transformation process. Includes 18 references, tables, figures.

Product Details

Edition:

Vol. - No.

Published:

11/01/2009

Number of Pages:

15

File Size:

1 file , 1000 KB