Phosphonate- and carboxylate-based chelating agents that solubilize (hydr)oxide-bound MnIII
1Department of Geography and Environmental Engineering, The Johns Hopkins University, 3400 North Charles Street, Baltimore, Maryland 21218, USA. yunwang@mit.edu
Environmental Science & Technology
|July 9, 2008
Summary
Synthetic phosphonate chelators can release dissolved manganese (MnIII) from mineral oxides in natural waters. Chelator structure predicts MnIII release, impacting aquatic redox processes.
Area of Science:
- Environmental Chemistry
- Geochemistry
- Aquatic Chemistry
Background:
- Dissolved manganese (MnIII) is suggested to be ubiquitous at oxic/anoxic interfaces in natural waters.
- MnIII plays crucial roles in aquatic biogeochemical redox processes.
Purpose of the Study:
- To identify environmentally relevant synthetic phosphonate-based chelators that solubilize (hydr)oxide-bound MnIII.
- To understand how chelator structure influences MnIII release and predict dissolution rates.
Main Methods:
- Investigated ligand-promoted dissolution of manganite and birnessite with pyrophosphoric acid (PP), methylenediphosphonic acid (MDP), and phosphonoacetic acid (PAA) at circum-neutral pH.
- Assessed the reactivity of aminophosphonate/carboxylate chelators with manganite.
Main Results:
- Ligand-promoted dissolution was predominant from pH 6-8.
- Dissolution rates and MnIII concentrations decreased in the order PP > MDP > PAA.
- At pH 5, MDP showed high reactivity, while methyliminodiacetic acid reduced MnIII to MnII.
Conclusions:
- Synthetic phosphonate chelators effectively release aqueous MnIII from mineral oxides.
- Chelator structure is a key factor in predicting MnIII release efficiency and potential redox transformations.
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