58
6 Effect of Temperature on Uranium Mobile Species
in the Soils
The objects of the study were samples (0–20)-cm of soils of sod-podzolic light
loamy (coarse sandy) and peaty lowland type, containing predominantly uranium of
natural origin. Samples of soils were selected in the summer of 2016 in the
Drogichinsky district of the Brest region and in the Minsk district of the Minsk
region. The main characteristics of soil samples are given in Table 7.
The sample of organic soil (T) was more acidic than the sample of mineral soil
(SP). The water capacity (WC), the content of organic components (TOM), mobile
calcium (Ca mob ), and potassium (K mob ) in peaty soil were significantly higher than in
sod-podzolic light loamy soil. The fraction of physical clay in the sod-podzolic soil
was 24 wt. %.
In the soils, uranium isotopes
238
U,
235
U, and
234
U were present in the ratio by
activity, which was practically not different from the natural one. The ratio of
238
U/
234
U by activity was 1.0. The total activity of the uranium in the soil samples
estimated by activities of
238
U and
234
U, as the contribution of
235
U to the total soil
activity was insignificant. The total content of uranium in the sod-podzolic light
loamy soil was three times greater than in the peaty soil.
In laboratory conditions, two series of experiments with the air-dry and the
water-saturated soil samples were performed. The soil samples were held for three
weeks at specified temperatures in the range from −18 to +30 °C. Humidity of soil
samples was controlled by their weight. The content of U mob in soils was established
by the method of radiochemical analysis of soil extracts with acetate-ammonium
buffer solution (pH 4.8). The soil samples were treated by an extracting solution
after the soil temperature was adjusted to (20 ± 2) °C. The obtained extracts were
passed through the paper filters "blue tape".
Change in the content of U mob in air-dry soil samples at varying temperature
conditions. In air-dry conditions in the temperature range from −18 to +30 °C, the
U mob content in sod-podzolic light loamy soil was in the range from (1.6 ± 0.2) to
(2.7 ± 0.2) Bq kg
−1
of solid matter, and in peaty soil—from (0.87 ± 0.10) to
(3.0 ± 0.2) Bq kg
−1
. Under these conditions, the portion of U mob in the sod-podzolic
soil varied in the interval from (4.6 ± 0.6) to (7.4 ± 0.7)%, and in peaty soil—from
(7.5 ± 0.7) to (26 ± 3)%. The results of the change in the portion of U mob in soils after
their aging at various temperatures in the air-dry state are given in Fig. 8.
As can be seen from Fig. 8, in both soils the portion of U mob increased with
increasing temperature from −18 to +15 °C. In this interval in soddy- podzolic soil,
the portion of U mob increased by approximately 20% and in peaty soil more than
twice. With a further rise in temperature to +30 °C, the portion of U mob in soils
decreased compared to the levels reached at +15 °C: in light loamy soil by 1.7 times
and in peaty soil by more than 3 times. The increase in the content of U mob in air-dry
soils with increasing temperature from −18 to +15 °C can be explained by an
increase in the intensity of ion-exchange processes at the boundary of the solid
phase of ‘the soil–the soil pore solution’. Reduction of their content in the soils with
G. A. Sokolik et al.
6 Effect of Temperature on Uranium Mobile Species
in the Soils
The objects of the study were samples (0–20)-cm of soils of sod-podzolic light
loamy (coarse sandy) and peaty lowland type, containing predominantly uranium of
natural origin. Samples of soils were selected in the summer of 2016 in the
Drogichinsky district of the Brest region and in the Minsk district of the Minsk
region. The main characteristics of soil samples are given in Table 7.
The sample of organic soil (T) was more acidic than the sample of mineral soil
(SP). The water capacity (WC), the content of organic components (TOM), mobile
calcium (Ca mob ), and potassium (K mob ) in peaty soil were significantly higher than in
sod-podzolic light loamy soil. The fraction of physical clay in the sod-podzolic soil
was 24 wt. %.
In the soils, uranium isotopes
238
U,
235
U, and
234
U were present in the ratio by
activity, which was practically not different from the natural one. The ratio of
238
U/
234
U by activity was 1.0. The total activity of the uranium in the soil samples
estimated by activities of
238
U and
234
U, as the contribution of
235
U to the total soil
activity was insignificant. The total content of uranium in the sod-podzolic light
loamy soil was three times greater than in the peaty soil.
In laboratory conditions, two series of experiments with the air-dry and the
water-saturated soil samples were performed. The soil samples were held for three
weeks at specified temperatures in the range from −18 to +30 °C. Humidity of soil
samples was controlled by their weight. The content of U mob in soils was established
by the method of radiochemical analysis of soil extracts with acetate-ammonium
buffer solution (pH 4.8). The soil samples were treated by an extracting solution
after the soil temperature was adjusted to (20 ± 2) °C. The obtained extracts were
passed through the paper filters "blue tape".
Change in the content of U mob in air-dry soil samples at varying temperature
conditions. In air-dry conditions in the temperature range from −18 to +30 °C, the
U mob content in sod-podzolic light loamy soil was in the range from (1.6 ± 0.2) to
(2.7 ± 0.2) Bq kg
−1
of solid matter, and in peaty soil—from (0.87 ± 0.10) to
(3.0 ± 0.2) Bq kg
−1
. Under these conditions, the portion of U mob in the sod-podzolic
soil varied in the interval from (4.6 ± 0.6) to (7.4 ± 0.7)%, and in peaty soil—from
(7.5 ± 0.7) to (26 ± 3)%. The results of the change in the portion of U mob in soils after
their aging at various temperatures in the air-dry state are given in Fig. 8.
As can be seen from Fig. 8, in both soils the portion of U mob increased with
increasing temperature from −18 to +15 °C. In this interval in soddy- podzolic soil,
the portion of U mob increased by approximately 20% and in peaty soil more than
twice. With a further rise in temperature to +30 °C, the portion of U mob in soils
decreased compared to the levels reached at +15 °C: in light loamy soil by 1.7 times
and in peaty soil by more than 3 times. The increase in the content of U mob in air-dry
soils with increasing temperature from −18 to +15 °C can be explained by an
increase in the intensity of ion-exchange processes at the boundary of the solid
phase of ‘the soil–the soil pore solution’. Reduction of their content in the soils with
G. A. Sokolik et al.