There is a general sequence of exchangeable cations going from the least to greatest affinity for an exchange site. The greater the charge, the greater the affinity. Microorganisms speed up these reaction. Using these reactions for metabolic energy. Even so, concentration of microorganisms is generally low so that these are still slow relative to other chemical processes.
Oxidation involves the loss of an electron while reduction involves the gain of an electron.
The term pe is used to describe the electron activity while Eh, the redox potential, is a voltage measurement. Some elements are isotopically unstable and spontaneously decay to more stable isotopes. This decay is of three types.