1. Pb Solids Precipitated Under Laboratory Conditions
Comparison Between Synthesized Lead Particles and Lead Solids Formed on Surfaces in Real Drinking Water Distribution Systems
Mallikarjuna N. Nadagouda1, Darren Lytle2* and Michael Schock2
1Pegasus Technical Services, 46 E Hollister Street, Cincinnati, Ohio 45219
2NRMRL, WSWRD, U. S. Environmental Protection Agency, 26 West Martin Luther King Drive Cincinnati, Ohio 45268
Introduction
Pb Solids Precipitated Under Laboratory Conditions
Lead Pipe Scale Analysis
Phosphates are important inhibitors in the prevention of calcium scale build-up and iron precipitation in water distribution systems, and research on the subject has been ongoing for many years.
In 1991, the U.S. Environmental Protection Agency’s (U.S. EPA) Lead and Copper rule established an action level for lead at the consumer’s tap of mg/L in a one liter first-draw sample.
The objective of this work is to use synthesized lead particles and solids to document the important transformation from Pb(II) to Pb(IV) in chlorinated water, with the intent of representing the formation of Pb(IV) species in drinking water lead pipes over time and a focus on the morphological and crystalline features. The results will likely provide a better understanding of how corrosion by-product scales form on lead pipes, and the dissolution of lead into DWDS.
Figure 4. SEM images of lead crystals grown on the surface of lead pipe at (a) pH 6.5 without inhibitor, (b) pH 6.5 with phosphate inhibitor, (c) pH 7 without inhibitor and (d) pH 7 with phosphate inhibitor.
Figure 7. SEM images of lead crystals grown on the surface of lead pipe at (a) pH 8.5 without inhibitor, (b) pH 8.5 with phosphate inhibitor, (c) pH 9 without inhibitor and (d) pH 9 with phosphate inhibitor.
Figure 10. X-ray mapping of images of lead crystals grown on the surface of lead pipe at (a) pH 8.5 (blue-lead and red-carbon) without inhibitor, (b) pH 8.5 (blue-lead, red-carbon and green-oxygen) with phosphate inhibitor, (c) pH 9 (blue-lead, red-phosphorous and green-calcium) and (d) pH 9 (blue-lead, red-carbon and green-oxygen) with inhibitor.
Experimental
Lead Particles Synthesis
Figure 1. SEM images of aged cerrusite samples.
The synthesis of PbO2 was conducted in a one liter glass beaker at room temperature (~23°C). Sodium bicarbonate, sodium chloride, and sodium hypochlorite were added to one liter of deionized water at initial concentration goals of 10 mg C/L, 300 mg Cl-/L and 3 mg Cl2/L, respectively. The titration system was programmed to maintain the test water at pH Once stabilized, lead chloride was added to provide an initial lead concentration of 20 mg/L.
Conclusions
We have shown possible tendencies for the transformation of hydrocerussite, [Pb3(CO3)2(OH)2], to cerussite, PbCO3, and the Pb(IV) oxides plattnerite, ß-PbO2, and scrutinyite, α-PbO2, i.e. Pb(II) to Pb(IV) compounds. With lead pipe scale analysis, it was found that at lower pH (6 to 7) the formation of different shapes, such as nanorods, micro-rods and dendritic structures, were favored with and without inhibitor. However, an increase in pH ≥ 8 with orthophosphate inhibitor started the formation of spheres and of a uniform layer of phosphate/PbCO3 coating. Different crystal growth at higher pH, when contrasted with lower pH, was not observed.
Lead Pipe Loop Study
The experiments were conducted in recirculating systems comprised of fifty-five gallon polyethylene tanks with floating lids. Water used for the study was building DI water amended with sodium bicarbonate, potassium chloride and calcium chloride. Dissolved inorganic carbon (DIC) was maintained at 100 mg/L as carbon. The pH was adjusted and maintained by adding HCl and/or NaOH, as needed. Stock solutions of orthophosphate inhibitors were prepared at concentrations of 3.0 mg/L using NaH2PO4, and the experiments were done in pairs (with vs. without PO4) for pH 6.5, 7.0, 7.5, 8.0, 8.5 and 9.0, respectively (see Table-1).
Figure 8. TEM images of lead crystals grown at (a) pH 6.5 with phosphate inhibitor, (b) pH 7 without inhibitor, (c) pH 7.5 with phosphate inhibitor and (d) pH 8 with phosphate inhibitor.
Figure 5. SEM images of lead crystals grown on the surface of lead pipe at (a) pH 7.5 without inhibitor, (b) pH 7.5 with phosphate inhibitor, (c) pH 8 without inhibitor and (d) pH 8 with phosphate inhibitor.
Figure 2. TEM images of (a) precipitated hydrocerussite and (b) aged cerussite samples.
Notice
The U.S. Environmental Protection Agency, through its Office of Research and Development, funded and managed, or partially funded and collaborated in, the research described herein. It has been subjected to the Agency’s peer and administrative review and has been approved for external publication. Any opinions expressed are those of the author (s) and do not necessarily reflect the views of the Agency, therefore, no official endorsement should be inferred. Any mention of trade names or commercial products does not constitute endorsement or recommendation for use.
Table-1
/25/2006 7/9/2007
Yes 3/25/2006 7/9/2007
/25/2006 3/6/2007
Yes 3/25/2006 3/6/2007
/25/2006 3/6/2007
Yes 3/25/2006 3/6/2007
/25/2006 3/6/2007
Yes 3/25/2006 3/6/2007
/25/2006 3/6/2007
Yes 3/25/2006 3/6/2007
/25/2006 3/6/2007
Yes 3/25/2006 3/6/2007
Loop pH, PO4aded Start End
Figure 9. X-ray mapping image of lead pipe at (a) pH 6.5 with inhibitor (red-phosphorous and green- calcium), (b) with inhibitor pH 6.5 (blue-lead, red-carbon and green-oxygen), (c) pH 7 with inhibitor (red-phosphorous and green- calcium) and (d) pH 7 with inhibitor (red-lead, green-oxygen and blue-carbon).
Figure 3. XRD patterns of (a) hydrocerussite (Pb3(CO3)2(OH)2) aged for 14 days (i.e cerussite) (b) precipitated hydrocerussite (Pb3(CO3)2(OH)2). H= hydrocerussite, pattern No , C= cerussite, pattern , P = plattnerite, pattern , and S = scrutinyite, pattern
Figure 6. Selected area diffraction pattern (SAED) of lead crystals grown at (a) pH 6.5 with phosphate inhibitor, (b) pH 7 without inhibitor, (c) pH 7.5 with phosphate inhibitor and (d) at pH 8 with phosphate inhibitor.