57
In organic soils, the K d coefficient varied over a wider range (430–2.780) than in
mineral soils. The sorption capacity of these soils with respect to uranium increased
in the following order: peat-bog soil from P3 plot—peaty soil from P5 plot—peatygley soil from P6 plot—peat-bog soil from P4 plot.
The organic soils differed significantly in the content and structure of organic
components, water capacity, and acidity. In the different species of peat-bog soils,
content of organic matter varied in the range of 21.7–76.6 wt. %, the value of water
capacity, 114–550 wt. %; and pH KCl , in the range of 4.3–5.9.
In general, the most species of peaty-bog soils had a high sorption capacity with
respect to uranium. The processes of hydrolysis and formation of complex uranium
compounds with organic and inorganic constituents of the soil have a significant
effect on the ability of soils to fix uranium.
In organic soils, the fixation of uranium significantly depended on the ratio of
soluble and hardly soluble organic and organomineral components and the acidity
of the soil medium. An increase in the portion of hardly soluble organic and
organomineral components in the organic matter of the soil and a decrease in the
acidity of the soil medium can explain the increase in the value of K d coefficient in
the aforementioned series of peat-bog type soils, which indicated an increase in the
degree of fixation of uranium in this order (Sokolik et al. 2010).
The sorption properties of the soils of the peat-bog type basically determine
high-molecular-weight HA. In soils, most of the FA is usually associated with
high- molecular- weight HA and the mineral part of the sorption soil complex
(Ponomareva and Plotnikova 1980; Sokolik et al. 2002). Only a small part (0.2–
2.1%) of the total organic matter of the soil enters the soil pore waters (Table 6).
Basically, these are relatively low-molecular-weight organic components, with
which uranium is able to form complex compounds (Katz et al. 1991; Sparovek
et al. 2002).
The fixation of the main part of uranium by an organomineral complex of soils
limits its distribution in the soil and its entry into groundwater and vegetation.
However, the barrier functions of soils also depend on the depth of groundwater, the
degree of soil moistening, and the intensity of the redistribution of moisture along
the soil profile (Titayeva and Taskayev 1983).
With excessive soil moistening under anaerobic conditions, the content of mobile
forms of iron increases as a result of the reduction of Fe (III) to Fe (II), which can
lead to a decrease in the degree of fixation of uranium in soils (Nikolayeva and
Yeremina 2001; Luo and Gu 2009).
The obtained information on the content of uranium in the migratory-active,
exchangeable, and mobile (conventionally biologically accessible) forms in the
soils, as well as on the values of the uranium distribution coefficient between the
solid phase and the porous soil solution, can be used for parametrization of models
for forecasting the redistribution of uranium in soil media and pollution levels of
natural waters and biological communities.
Uranium and Its Distribution in Typical Belarusian Soils
In organic soils, the K d coefficient varied over a wider range (430–2.780) than in
mineral soils. The sorption capacity of these soils with respect to uranium increased
in the following order: peat-bog soil from P3 plot—peaty soil from P5 plot—peatygley soil from P6 plot—peat-bog soil from P4 plot.
The organic soils differed significantly in the content and structure of organic
components, water capacity, and acidity. In the different species of peat-bog soils,
content of organic matter varied in the range of 21.7–76.6 wt. %, the value of water
capacity, 114–550 wt. %; and pH KCl , in the range of 4.3–5.9.
In general, the most species of peaty-bog soils had a high sorption capacity with
respect to uranium. The processes of hydrolysis and formation of complex uranium
compounds with organic and inorganic constituents of the soil have a significant
effect on the ability of soils to fix uranium.
In organic soils, the fixation of uranium significantly depended on the ratio of
soluble and hardly soluble organic and organomineral components and the acidity
of the soil medium. An increase in the portion of hardly soluble organic and
organomineral components in the organic matter of the soil and a decrease in the
acidity of the soil medium can explain the increase in the value of K d coefficient in
the aforementioned series of peat-bog type soils, which indicated an increase in the
degree of fixation of uranium in this order (Sokolik et al. 2010).
The sorption properties of the soils of the peat-bog type basically determine
high-molecular-weight HA. In soils, most of the FA is usually associated with
high- molecular- weight HA and the mineral part of the sorption soil complex
(Ponomareva and Plotnikova 1980; Sokolik et al. 2002). Only a small part (0.2–
2.1%) of the total organic matter of the soil enters the soil pore waters (Table 6).
Basically, these are relatively low-molecular-weight organic components, with
which uranium is able to form complex compounds (Katz et al. 1991; Sparovek
et al. 2002).
The fixation of the main part of uranium by an organomineral complex of soils
limits its distribution in the soil and its entry into groundwater and vegetation.
However, the barrier functions of soils also depend on the depth of groundwater, the
degree of soil moistening, and the intensity of the redistribution of moisture along
the soil profile (Titayeva and Taskayev 1983).
With excessive soil moistening under anaerobic conditions, the content of mobile
forms of iron increases as a result of the reduction of Fe (III) to Fe (II), which can
lead to a decrease in the degree of fixation of uranium in soils (Nikolayeva and
Yeremina 2001; Luo and Gu 2009).
The obtained information on the content of uranium in the migratory-active,
exchangeable, and mobile (conventionally biologically accessible) forms in the
soils, as well as on the values of the uranium distribution coefficient between the
solid phase and the porous soil solution, can be used for parametrization of models
for forecasting the redistribution of uranium in soil media and pollution levels of
natural waters and biological communities.
Uranium and Its Distribution in Typical Belarusian Soils