Lead concentrations in drinking water distribution systems are influenced by the dissolution,
precipitation, and transformation of lead corrosion products that are present as scale in
distribution system pipe. Changes in treatment processes that influence the distribution system
water chemistry can induce the dissolution or transformation of the lead-containing corrosion
products. The addition of orthophosphate as a corrosion inhibitor has been demonstrated in
previous work to limit the dissolved concentrations of lead to below the action level established
by the Lead and Copper Rule. In this research, the role of orthophosphate in controlling
the dissolution rates of the lead carbonate hydrocerussite and the lead phosphate
hydroxylpyromorphite were evaluated in controlled laboratory-scale experiments using
continuous-flow stirred tank reactors. Dissolution rates are interpreted within a reaction-based
approach that considers the overall thermodynamic driving force for dissolution as part of a
fundamental dissolution rate equation. The solid phases remaining at the conclusion of selected
experiments were characterized by scanning electron microscopy and X-ray diffraction to assess
transformations in the solid phases that may have been induced by orthophosphate. Low
intrinsic solubility and dissolution rates were observed for hydroxylpyromorphite. These
observations suggest that the formation of hydroxylpyromorphite can decrease dissolved lead
concentrations in distribution system waters. The presence of orthophosphate during the
dissolution of hydrocerussite dramatically decreased the rate of lead release to solution. Includes 9 references, figures.
| Edition : | Vol. - No. |
| File Size : | 1
file
, 780 KB |
| Note : | This product is unavailable in Ukraine, Russia, Belarus |
| Number of Pages : | 7 |
| Published : | 11/01/2008 |
