Conference paper

Surface Complexation and Its Impact on Geochemical Kinetics

Werner Stumm ; Institute for Water Resources and Water Pollution Control (EAW.4.G), and Institute of Aquatic Sciences, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland
Bernhard Wehrli ; Institute for Water Resources and Water Pollution Control (EAW.4.G), and Institute of Aquatic Sciences, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland
Erich Wieland ; Institute for Water Resources and Water Pollution Control (EAW.4.G), and Institute of Aquatic Sciences, Swiss Federal Institute of Technology (ETH), Zurich, Switzerland

Abstract

The weathering of rocks, the formation of soils, the alteration
and dissolution of sediments are a consequence of surface reac-.
tions. Furthermore, many redox processes such as the oxidation of
V02+, Mn2+ and Fe2+, the ncn-biotic degradation of organic substances and photosensitized processes are catalyzed by surfaces.
The electric double layer theory, despite its efficiency in quantifying
certain phenomena of colloid stability, has limitations because
it neglects chemical speciation at the surface and does not provide
information on the chemical structure of the interfacial region. The
surfaces of naturally occurring solids are characterized by functional
groups, e. g., OH- groups on the surface of hydrous oxides at
on organic surfaces. Specific adsorption of - or interaction with
- H+, OH-, metal ion s and ligands occurs through coordination at
the surface; inner-sphere surface complexes can be formed. The
form of occurrence of the individual compounds (speciation) needs
to be known in order to understand their reactivity; especially the
geometry of the coordination shell of surface sites or of reactants
at surfaces is a prerequisite for interpreting reaction rates occuring
at the particle-water interface. Some case studies on the oxidation of Mn2+ and V02+ and on the dissolution of hydrous oxides and silicates are presented. In each case, the kinetics of the processes and how it is affected by solution variables such as H+ and ligands (such as oxalate and other di- ar hydroxy-carboxylates) are explained by simple mechanistic models that involve the coordination at the mineral-solution interface. Simple rate laws are derived illustrating the rates' dependence on the concentration (activity) of surface species.

Keywords

Hrčak ID:

176370

URI

https://hrcak.srce.hr/176370

Publication date:

25.8.1987.

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