The sulfur content of the lithosphere is estimated at 600 ppm. Sulfur in
soils is highly variable and generally ranges from 30 to 10,000 ppm with
an estimated average of 700 ppm. Since sulfur is essential for all living organisms,
it has been widely studied. Many of the reactions of sulfur in soils are closely associated with organic matter and the activity of microorganisms.
The most common form of sulfur in soils is SO“. Since sulfur occurs in
many different oxidation states, redox relationships must be considered in
dealing with its overall stability and mineral transformations.
In this chapter the solubility relationships of the various sulfur species
and the sequence of metal sulfide precipitations will be critically examined.
These developments are of particular interest in submerged soils and in
soils where the cycling of heavy metals is exposed to fluctuating redox
conditions. Complexes of sulfate are included in the separate chapters dealing
with the respective cations.
17.1 EFFECT OF REDOX ON SULFUR SPEC IATION