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Polyphosphate Adsorption and Hydrolysis on Aluminum Oxides
Biao Wan1, Rixiang Huang1, Julia M Diaz2
1School of Earth and Atmospheric Sciences , Georgia Institute of Technology , 311 Ferst Drive , Atlanta , Georgia 30332-0340 , United States.
Environmental Science & Technology
|July 18, 2019
Summary
Divalent metal cations significantly enhance polyphosphate hydrolysis on aluminum oxides, influencing phosphorus cycling. Calcium ions showed the strongest effect, with hydrolysis rates decreasing as mineral particle size increased.
Area of Science:
- Geochemistry
- Environmental Science
- Surface Chemistry
Background:
- Understanding phosphorus (P) mobility and bioavailability is crucial for environmental management.
- Phosphate species at mineral-water interfaces dictate phosphorus fate and transformation.
- Polyphosphates are important long-chained phosphate molecules relevant to environmental P cycling.
Purpose of the Study:
- Investigate the sorption and hydrolysis of polyphosphate on aluminum oxides.
- Determine the influence of divalent metal cations (Ca2+, Cu2+, Mg2+, Mn2+, Zn2+) on polyphosphate behavior.
- Assess the effect of aluminum oxide particle size on polyphosphate hydrolysis and speciation.
Main Methods:
- Utilized gamma-aluminum oxide (γ-Al2O3) with varying particle sizes (5, 35, 70 nm).
- Studied polyphosphate interactions in the presence of divalent metal cations at pH 6-8.
- Employed solid-state 31P nuclear magnetic resonance (NMR) spectroscopy for surface species analysis.
Main Results:
- All tested metal cations enhanced polyphosphate hydrolysis, with Ca2+ exhibiting the most significant effect.
- Hydrolysis rate decreased with increasing mineral particle size in the presence of Ca2+.
- Identified amorphous calcium phosphate precipitates, inner-sphere complexes, and non-bonded phosphate groups on the mineral surface.
Conclusions:
- Divalent metal cations and mineral-water interface processes critically control polyphosphate speciation and transformation.
- These interactions play a vital role in regulating phosphorus cycling in natural environments.
- Polyphosphate hydrolysis is influenced by cation-polyphosphate affinity and mineral surface characteristics.
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