Oxidation of lead sulfide surfaces in the presence of phosphate: nanoparticle formation.
EMSL Project ID
4990
Abstract
The understanding of galena (PbS) oxidation in the presence of phosphate containing solutions is important because lead contaminated soils and mine wastes are often treated with phosphate as a remediation strategy. This treatment leads to the formation of insoluble lead-phosphates, thereby immobilizing the lead and preventing the spread of contamination. However at this point, there is not much known about the growth of the lead-phosphate secondary phases on the atomic scale. Using electrochemical scanning tunneling microscopy (EC-STM), we have observed the growth of a secondary phase during the oxidation of galena (lead sulfide) surfaces in the presence of phosphate containing solutions. At low phosphate concentrations (~1-2 uM), we observe the formation of nanoparticles on the order of 2-50 nm across that appear to be, in some cases, oriented crystallographically on the galena surface. At high concentrations (100 uM), we observe a much more massive amount of precipitation. We hypothesize that the secondary phase that is forming is a lead-phosphate of some kind, possibly pyromorphite. Therefore we propose to perform at EMSL X-ray photoelectron spectroscopy (XPS), with the goal of getting a detailed understanding of the composition and oxidation state of sulfur and lead, and to determine if phosphate can be detected on the surface. We will react galena samples in the presence of four differerent solutions of varying composition (no phosphate, 1 uM phosphate, 10 uM phosphate, and 100 uM phosphate) and vary the time of reaction. Besides the XPS, we will require access to a potentiostat and an oxygen-free environment (house nitrogen will suffice) to react the samples immediately before analysis in the XPS.
Project Details
Project type
Exploratory Research
Start Date
2003-10-01
End Date
2005-10-06
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members
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