NH
þ
4 þ 2H 2 O $ NO
À
2 þ 6e
À
þ 8H
þ
ð1:15Þ
NO
À
2 þ H 2 O $ NO
À
3 þ 2e
À
þ 2H
þ
ð1:16Þ
Oxidation/reduction of Fe
2+ according to (Eq. 1.11) and subsequent hydrolysis
Fe
3þ
þ 3H 2 O $ Fe OH
ð Þ 3 þ 3H
þ
ð1:17Þ
The dissolution of pyrite as an important reservoir of reduction capacity is illustrated
in Fig. 1.2.
Changes in the pH of an environment may be caused by redox reactions but not
vice versa. Nevertheless, changes in the pH are usually buffered by the carbonate
system in the natural processes. The buffer capacity is the ability of the solution to
withstand the addition of an acid or alkali and maintain a near constant pH. It is
highest in situations where concentrations of acids and conjugated (linked) bases are
comparable. A solution is least buffered in a situation where the concentration of the
acid and the conjugated base differs most (one form is mostly present in the
solution). Therefore, acidity and alkalinity are important parameters of the natural
environment and can fundamentally influence the remedial action conducted by
chemically supported technologies.
The Eh value determines the activity of electrons in the natural environment. The
greatest electron activity (pε) is in a reducing environment and decreases in an
increasing oxidation environment. In natural systems, the general sequence of
reduction processes—the so-called redox ladder—applies when a tiered profile of
the pε develops, which is valid for a certain time and position until the relevant
oxidant is consumed.
The general classification of a redox environment is usually determined by the
source of oxygen. In an oxic environment, the source of the oxidation capacity is O 2
Fig. 1.2 Dissolution of pyrite
1 Geochemical Principles of Reductive Remediation Processes
11
þ
4 þ 2H 2 O $ NO
À
2 þ 6e
À
þ 8H
þ
ð1:15Þ
NO
À
2 þ H 2 O $ NO
À
3 þ 2e
À
þ 2H
þ
ð1:16Þ
Oxidation/reduction of Fe
2+ according to (Eq. 1.11) and subsequent hydrolysis
Fe
3þ
þ 3H 2 O $ Fe OH
ð Þ 3 þ 3H
þ
ð1:17Þ
The dissolution of pyrite as an important reservoir of reduction capacity is illustrated
in Fig. 1.2.
Changes in the pH of an environment may be caused by redox reactions but not
vice versa. Nevertheless, changes in the pH are usually buffered by the carbonate
system in the natural processes. The buffer capacity is the ability of the solution to
withstand the addition of an acid or alkali and maintain a near constant pH. It is
highest in situations where concentrations of acids and conjugated (linked) bases are
comparable. A solution is least buffered in a situation where the concentration of the
acid and the conjugated base differs most (one form is mostly present in the
solution). Therefore, acidity and alkalinity are important parameters of the natural
environment and can fundamentally influence the remedial action conducted by
chemically supported technologies.
The Eh value determines the activity of electrons in the natural environment. The
greatest electron activity (pε) is in a reducing environment and decreases in an
increasing oxidation environment. In natural systems, the general sequence of
reduction processes—the so-called redox ladder—applies when a tiered profile of
the pε develops, which is valid for a certain time and position until the relevant
oxidant is consumed.
The general classification of a redox environment is usually determined by the
source of oxygen. In an oxic environment, the source of the oxidation capacity is O 2
Fig. 1.2 Dissolution of pyrite
1 Geochemical Principles of Reductive Remediation Processes
11