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Pyromorphite growth on lead-sulfide surfaces.
Andrew G Stack1, Rolf Erni, Nigel D Browning
1Department of Land, Air and Water Resources, University of California, Davis, California 95616, USA.
Environmental Science & Technology
|December 4, 2004
Summary
This study reveals how pyromorphite nanoparticles form on galena surfaces during oxidation. These tiny particles, crucial in environmental lead mobility, grow epitaxially and can passivate the galena surface.
Area of Science:
- Geochemistry
- Materials Science
- Environmental Science
Background:
- Galena (PbS) is a primary lead ore mineral.
- Oxidation of galena can lead to the formation of secondary lead minerals.
- Understanding lead mineral formation is critical for assessing lead mobility and bioavailability in the environment.
Purpose of the Study:
- To investigate the nucleation and growth mechanisms of pyromorphite particles on a galena substrate under oxidative conditions.
- To determine the influence of solution chemistry and oxidation potential on particle characteristics.
- To elucidate the role of pyromorphite formation in the passivation of galena surfaces.
Main Methods:
- Electrochemical Scanning Tunneling Microscopy (EC-STM) for in-situ imaging of nucleation and growth.
- Electron microscopy for detailed particle characterization.
- Cyclic voltammetry to study surface passivation phenomena.
Main Results:
- Observed the formation of 10-15 nm pyromorphite particles on galena under oxidative conditions.
- Demonstrated that particle size and morphology are significantly influenced by solution parameters and oxidation potential.
- Provided evidence for epitaxial growth of pyromorphite on galena, including preferred crystallographic orientation and adherence.
- Showed that phosphate presence partially passivates the galena surface against oxidation.
Conclusions:
- Pyromorphite nanoparticles form epitaxially on galena, with size and morphology controlled by environmental conditions.
- Early-stage particles are small enough for potential mobilization in soil environments.
- Phosphate adsorption or pyromorphite nucleation inhibits galena oxidation, suggesting mechanisms for surface passivation.