properties. This creates a geochemical balance between the solvent (water), the
dissolved substance, and the rock matrix. Altering these conditions also leads to
changes in the water chemistry. A significant change in the environment is alkalinity,
which in natural waters is mainly a function of the sum of carbonate species and
OH
À . Therefore, the geochemical system has a certain inertia and, to some degree,
can buffer natural oscillations or cause anthropogenically induced changes.
The basic chemical processes used in remediation are mainly changes in acidalkaline conditions, redox conditions, or the concentration of species causing precipitation. Since the two basic components of chemical reactions are protons and
electrons, their exchanges in redox processes and acid-alkaline reactions are fundamental in nature. These processes, which are observed as a reaction of mineral
precipitation, weathering, dissolution, or organic matter decomposition, etc., are
fundamental reactions occurring on the surface of the earth’s crust because of the
contact between rock, water, and the atmosphere, and determine the parameters of the
surrounding environment. While the significance of pH for the toxicity and mobility
of hazardous substances (heavy metals, radionuclides, organic substances, etc.) has
been known for a long time, the importance of the redox potential has been significantly underestimated or even neglected except for the oxidation zone of ore deposits.
It is commonly assumed that pH is a critical parameter for the state of the natural
environment so the other parameters (redox potential, content of dissolved solids in
the aqueous environment, concentration of gases) play just a minor role. However, the
results of systematic studies on the natural environment and natural processes show
that the decisive factors in most cases are redox processes and pH, and the other
parameters are either directly determined or strongly influenced by these processes.
1.2 Stability of Redox Conditions
The stable redox environment in the geosphere is caused by biota that enables
photosynthetic processes. This biota synthesizes complex organic substances from
carbon dioxide using solar energy according to the following simplified equation of
photosynthesis (Eq. 1.1)
CO 2 þ H 2 O ! CH 2 O þ O 2
ð1:1Þ
where CH 2 O is a general formula for organic matter (like glucose C 6 H 12 O 6 ). During
the process, 472 kJ/mol of solar energy is consumed (Stumm and Morgan 1995) and
the energy is “stored” and subsequently used to secure the life processes of the biota.
When looking at the oxidation state (formal charge, valence) of the substance or
compound, reduction of carbon occurs through photosynthesis from oxidation state
(+IV) to (0) and an oxidation of oxygen from oxidation state –II to 0:
C
þIV O
ÀII
2 þ H 2 O ! C
0 H 2 O þ O
2
0
ð1:2Þ
4
M . Černík and J. Zeman
dissolved substance, and the rock matrix. Altering these conditions also leads to
changes in the water chemistry. A significant change in the environment is alkalinity,
which in natural waters is mainly a function of the sum of carbonate species and
OH
À . Therefore, the geochemical system has a certain inertia and, to some degree,
can buffer natural oscillations or cause anthropogenically induced changes.
The basic chemical processes used in remediation are mainly changes in acidalkaline conditions, redox conditions, or the concentration of species causing precipitation. Since the two basic components of chemical reactions are protons and
electrons, their exchanges in redox processes and acid-alkaline reactions are fundamental in nature. These processes, which are observed as a reaction of mineral
precipitation, weathering, dissolution, or organic matter decomposition, etc., are
fundamental reactions occurring on the surface of the earth’s crust because of the
contact between rock, water, and the atmosphere, and determine the parameters of the
surrounding environment. While the significance of pH for the toxicity and mobility
of hazardous substances (heavy metals, radionuclides, organic substances, etc.) has
been known for a long time, the importance of the redox potential has been significantly underestimated or even neglected except for the oxidation zone of ore deposits.
It is commonly assumed that pH is a critical parameter for the state of the natural
environment so the other parameters (redox potential, content of dissolved solids in
the aqueous environment, concentration of gases) play just a minor role. However, the
results of systematic studies on the natural environment and natural processes show
that the decisive factors in most cases are redox processes and pH, and the other
parameters are either directly determined or strongly influenced by these processes.
1.2 Stability of Redox Conditions
The stable redox environment in the geosphere is caused by biota that enables
photosynthetic processes. This biota synthesizes complex organic substances from
carbon dioxide using solar energy according to the following simplified equation of
photosynthesis (Eq. 1.1)
CO 2 þ H 2 O ! CH 2 O þ O 2
ð1:1Þ
where CH 2 O is a general formula for organic matter (like glucose C 6 H 12 O 6 ). During
the process, 472 kJ/mol of solar energy is consumed (Stumm and Morgan 1995) and
the energy is “stored” and subsequently used to secure the life processes of the biota.
When looking at the oxidation state (formal charge, valence) of the substance or
compound, reduction of carbon occurs through photosynthesis from oxidation state
(+IV) to (0) and an oxidation of oxygen from oxidation state –II to 0:
C
þIV O
ÀII
2 þ H 2 O ! C
0 H 2 O þ O
2
0
ð1:2Þ
4
M . Černík and J. Zeman