Because of the many questions surrounding the occurrence of tetravalent lead solids and
their relationships to lead release, this research investigation was initiated in 2002 in order to:
explore the water quality conditions and pathways that lead to the formation of PbO<sub>2</sub> in water
during long term precipitation experiments; and, to determine the possible sensitivity of PbO<sub>2</sub>
scales to treatment changes that would affect oxidation-reduction potential (ORP) by analyzing the stability of the solids in
response to changes in ORP. The physical properties, mineralogy, and solubility of lead solids at
several pH values in well chlorinated water were examined, and the effect of sulfate on PbO<sub>2</sub>
formation was also briefly investigated. A series of long-term precipitation experiments were conducted to evaluate the effects of water
chemistry and time on the mineralogy and corresponding solubilities of lead solids in water.
During these tests, redox conditions were chosen to represent the high end of realistic utility
practices and were maintained with the intent to form Pb(IV) solids (plattnerite and/or scrutinyite).
High redox potential of the water was maintained with free chlorine, which was replenished as
needed to maintain a goal concentration of 3 mg Cl<sub>2</sub>/L throughout most of the studies. Late into
the test runs, chlorine residuals were permitted to dissipate to test the reversibility of mineral phase
development. One run was performed in water containing sulfate to investigate the role of an
additional major anion on the development of lead solids. Lead (II) sulfate and hydroxl-carbonate-sulfate
solids have been observed in some lead drinking water pipes. All experiments were
conducted at room temperature (-23 ºC).
Lead aging studies were conducted in a 3.0 liter glass beaker. Secured at the top of the
beaker were pH and two redox electrodes, dissolved oxygen (DO) and temperature probes, a
mechanical stirrer and an injection line for both acid and base. The computer software recorded
pH values and titrant volumes. Data was collected on the pH, dissolved oxygen, redox potential,
free and total chlorine, and concentrations of lead, sulfur and total inorganic carbon. In addition the
crystalline phases of lead solids were identified using X-ray diffraction (XRD). Includes 26 references, table, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 360 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 14 |
| Published : | 11/01/2005 |
