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Phosphate bonding on noncrystalline Al/Fe-hydroxide coprecipitates
1Department of Soil Science, North Carolina State University, Raleigh, North Carolina 27695, United States.
Environmental Science & Technology
|July 1, 2011
Summary
This study reveals how orthophosphate bonds with aluminum and iron in poorly crystalline minerals. Understanding these sorption mechanisms is key for environmental remediation and nutrient management.
Area of Science:
- Geochemistry
- Environmental Science
- Materials Science
Background:
- Poorly crystalline minerals exhibit high sorption capacities for environmental contaminants.
- Molecular-level sorption mechanisms on complex mineral assemblages are not well understood.
Purpose of the Study:
- To determine orthophosphate (PO(4)) bonding distribution between aluminum (Al) and iron (Fe) in Al/Fe-hydroxide coprecipitates.
- To correlate PO(4) sorption with the structural properties of these coprecipitates.
Main Methods:
- Synthesized Al/Fe-hydroxide coprecipitates with varying Al proportions (0-100 mol%).
- Utilized Phosphorus X-ray Absorption Near Edge Structure (XANES) spectroscopy to analyze PO(4) bonding.
- Employed X-ray Photoelectron Spectroscopy (XPS) for near-surface metal distribution analysis.
- Applied X-ray Diffraction (XRD) and Fe Extended X-ray Absorption Fine Structure (EXAFS) to characterize structural properties.
Main Results:
- Orthophosphate showed preferential bonding with Al in coprecipitates containing 20 and 50 mol% Al.
- No metal preference for PO(4) bonding was observed at 75 mol% Al.
- Increasing Al proportion led to decreased structural ordering and smaller Fe-hydroxide domain sizes.
- Coprecipitate structure uniquely influenced PO(4) sorption compared to isolated hydroxides.
Conclusions:
- The structural characteristics of Al/Fe-hydroxide coprecipitates significantly control orthophosphate sorption behavior.
- Preferential orthophosphate binding to Al is influenced by the Al proportion and structural properties.
- These findings advance the understanding of nutrient and contaminant sorption in environmental systems.
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