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Analytical electron microscopy as a tool for accessing colloid formation process in natural waters
C Mondi1, K Leifer, D Mavrocordatos
1Institut de Chimie Minérale et Analytique, Université de Lausanne, CH-1015 Lausanne, Switzerland. christine.mondi@lmcp.jussieu.fr
Journal of Microscopy
|September 17, 2002
Summary
Analytical electron microscopy revealed that iron-rich colloids in peat soil drainage water are primarily organic matter. Iron oxy(hydr)oxides form with increased oxygen, with organic matter acting as nucleation sites for iron precipitation.
Area of Science:
- Environmental Science
- Geochemistry
- Materials Science
Background:
- Aquatic iron colloids play a crucial role in biogeochemical processes.
- Peat soils are unique environments with complex redox conditions.
- Understanding colloid composition is vital for water quality and metal transport.
Purpose of the Study:
- To characterize the composition and structure of iron-rich colloids in peat soil drainage water.
- To investigate the influence of redox conditions on colloid formation.
- To elucidate the role of organic matter in iron precipitation.
Main Methods:
- Analytical electron microscopy, including Transmission Electron Microscopy-Energy Dispersive Analyses (TEM-EDS).
- Electron Spectroscopic Imaging (ESI) and Electron Energy-Loss Spectroscopy (EELS) for elemental distribution.
- Characterization of colloids in both anoxic and oxygenated environments.
Main Results:
- Spherical entities (100-600 nm) found in anoxic water contained minimal iron.
- Increased oxygen led to the formation of iron oxy(hydr)oxides.
- Colloidal iron in oxygenated water was predominantly associated with organic matter (C+O > 90% at.).
- ESI and EELS showed iron and calcium concentrated on particle exteriors, while C and O followed spherical distribution.
- Nanometer-sized iron-rich phases indicated organic matter as nucleation sites.
Conclusions:
- Organic matter is the primary component of iron-rich colloids in this peat soil drainage system.
- Iron precipitation is significantly influenced by organic matter acting as nucleation sites.
- Redox conditions modulate the formation and association of iron oxy(hydr)oxides with organic colloids.
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