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PbO2(s, plattnerite) reductive dissolution by aqueous manganous and ferrous ions
1Department of Geography and Environmental Engineering, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA. zshi4@jhu.edu
Environmental Science & Technology
|June 24, 2009
Summary
Manganese and iron ions readily reduce lead(IV) oxide nanoparticles in water. Iron(II) can be hindered by iron oxides, but manganese can catalyze the reaction, impacting organic matter interactions.
Area of Science:
- Environmental Chemistry
- Geochemistry
- Materials Science
Background:
- Plattnerite (Pb(IV)O2) nanoparticle aggregates exist in aqueous suspensions.
- Understanding the reductive transformation of plattnerite is crucial for environmental remediation and contaminant fate studies.
Purpose of the Study:
- To investigate the reduction of Pb(IV)O2 nanoparticles by Fe(II) and Mn(II) ions in aqueous environments.
- To elucidate the role of Fe(III) and Mn(III)/Mn(IV) (hydr)oxides in modulating Pb(IV) reduction.
- To assess the impact of these redox reactions on the transformation of natural organic matter, using hydroquinone as a model.
Main Methods:
- Experimental investigation of Pb(IV)O2 nanoparticle reduction by Fe(II) and Mn(II) across a pH range of 3.0 to 8.5.
- Analysis of reaction products, including dissolved Pb(II) and oxidized metal species.
- Quantification of organic reductant (hydroquinone) and its oxidation product (p-benzoquinone) using High-Performance Liquid Chromatography (HPLC).
Main Results:
- Pb(IV)O2 nanoparticles are readily reduced by both Fe(II) and Mn(II), forming Pb(II).
- Fe(II) oxidation produces Fe(III) (hydr)oxides that inhibit Pb(IV) reduction, particularly at pH ≥ 5.
- Mn(II) oxidation yields mixed Mn(III)/Mn(IV) (hydr)oxides, which are less inhibitory. A Mn redox cycle can catalyze Pb(IV) reduction by Fe(II).
- Fe(II) addition prior to hydroquinone significantly reduces p-benzoquinone formation, while Mn(II) has minimal effect.
Conclusions:
- Fe(II) and Mn(II) are effective reductants for Pb(IV)O2 nanoparticles, with varying impacts on reaction kinetics and pathways.
- The formation of metal (hydr)oxides influences the persistence of Pb(IV) and the overall reaction efficiency.
- These redox processes can alter the reactivity of co-occurring organic matter, with implications for contaminant transport and transformation in aquatic systems.
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