ABSTRACT
Weathering of oxides and silicates have been studied extensively and illustrate the operation of surface-controlled reactions in the involved dissolution processes. Most of the metals and alloys used in today's civilization are thermodynamically unstable in contact with air because the oxidation reaction is exoergonic. Their widespread use rests on the development of a passive oxide film that blocks further reaction. The wide variety of properties spanned by metal oxides and their ready availability, make them the basis of many diverse classes of materials: pigments, magnetic materials, semiconductors, refractory ceramics, superconductors, etc. The redox chemistry of metal oxides requires the participation of a reductant or an oxidant. A more subtle, but important impact on the environment ensues because oxidants and reductants (organic matter) react in aquatic systems through the catalytic influence of the metal oxides in their cycles of redox dissolution and reprecipitation.
