the data suggest that metal concentrations in rad-Cs-contaminated sewage sludge
(samples 10–12, Table 29.1) were similar to those in the extracts of uncontaminated
sewage sludge (samples 1, 2, 4, 5, and 6, Table 29.1). Samples 8 and 9 (Table 29.1)
showed low metal concentrations as they were stabilized waste materials that were
treated to reduce heavy metal leaching.
The removals of Cs in different samples and test conditions are summarized in
Tables 29.2, 29.3, and 29.4. Table 29.2 shows Cs removal efficiencies (%) for
samples 1–7 under different pH and K-Fer concentrations without an addition of
metals. The tests were conducted for pH 3–10 and soluble Fer salt concentrations
0.1–1.0 mM. The results indicated that insoluble Fer complexes were formed with
metals present in the waste extracts (Table 29.1) upon addition of soluble K-Fer
salts, resulting in high Cs removal efficiencies. Fer complexes could be formed with
any of the metals such as Fe, Mn, Cu, and Zn present in sufficient concentrations
(Table 29.1) to precipitate 0.1 mM Fer ions. Cs removal in sample 7 was lower
(e.g., 74 % at pH 5) than those in other samples, although transition metals
(particularly Zn) in the sample were abundant for the formation of insoluble Fer
complexes. In a control experiment discussed in our previous work [4], we investigated on the effect of Zn concentration on Cs removal, and found that Cs removal
by Fer solids tends to be low when Zn is present at pH 5. Formation of the Zn-Fer
complex, which is known to have a comparatively low Cs distribution factor,
probably reduced Cs removal in the sample. The Cs removal in sample 7 at pH
3 increased to 92 %, possibly because of the formation of iron-Fer complex, which
has a high Cs distribution factor [4]. Moreover, Cs removal increased with increasing K-Fer concentration. However, this leads to increased amount of precipitate in
the solution, which is not preferable from the aspect of waste volume reduction.
Table 29.3 shows Cs removal from oxalic acid extracts. In a separate experiment, we examined the effect of oxalic acid concentration on Fer coprecipitation
method and concluded that for 0.1 mM Fer concentration, oxalic acid concentration
should be 0.01 M or less for precipitation of insoluble Fer compounds. In actual
waste extracts, oxalic acid is consumed by calcium present in the wastes, and hence
actual oxalic acid concentrations are lower than those in the original reagents. The
data in Table 29.3 show that Cs removal is possible with 20 times (nominal
concentration ¼ 0.05 M) as well as 10 times (nominal concentration ¼ 0.1 M)
dilutions of 1.0 M oxalic acid extract.
Table 29.3 Removal of cesium (Cs) from the 1 M oxalic acid extract with different dilution factor
applied before ferrocyanide (Fer) coprecipitation (the solution pH was 5 and Fer was 0.1 mM for
all samples)
Sample
code
100 times dilution (~0.01 M
oxalic acid)
20 times dilution
(~0.05 M oxalic acid)
10 times dilution
(~0.1 M oxalic acid)
3
9 7
9 9
9 3
4
9 7
9 5
9 3
5
9 5
9 7
9 6
6
9 8
9 5
9 2
338
Y. Fujikawa et al.
(samples 10–12, Table 29.1) were similar to those in the extracts of uncontaminated
sewage sludge (samples 1, 2, 4, 5, and 6, Table 29.1). Samples 8 and 9 (Table 29.1)
showed low metal concentrations as they were stabilized waste materials that were
treated to reduce heavy metal leaching.
The removals of Cs in different samples and test conditions are summarized in
Tables 29.2, 29.3, and 29.4. Table 29.2 shows Cs removal efficiencies (%) for
samples 1–7 under different pH and K-Fer concentrations without an addition of
metals. The tests were conducted for pH 3–10 and soluble Fer salt concentrations
0.1–1.0 mM. The results indicated that insoluble Fer complexes were formed with
metals present in the waste extracts (Table 29.1) upon addition of soluble K-Fer
salts, resulting in high Cs removal efficiencies. Fer complexes could be formed with
any of the metals such as Fe, Mn, Cu, and Zn present in sufficient concentrations
(Table 29.1) to precipitate 0.1 mM Fer ions. Cs removal in sample 7 was lower
(e.g., 74 % at pH 5) than those in other samples, although transition metals
(particularly Zn) in the sample were abundant for the formation of insoluble Fer
complexes. In a control experiment discussed in our previous work [4], we investigated on the effect of Zn concentration on Cs removal, and found that Cs removal
by Fer solids tends to be low when Zn is present at pH 5. Formation of the Zn-Fer
complex, which is known to have a comparatively low Cs distribution factor,
probably reduced Cs removal in the sample. The Cs removal in sample 7 at pH
3 increased to 92 %, possibly because of the formation of iron-Fer complex, which
has a high Cs distribution factor [4]. Moreover, Cs removal increased with increasing K-Fer concentration. However, this leads to increased amount of precipitate in
the solution, which is not preferable from the aspect of waste volume reduction.
Table 29.3 shows Cs removal from oxalic acid extracts. In a separate experiment, we examined the effect of oxalic acid concentration on Fer coprecipitation
method and concluded that for 0.1 mM Fer concentration, oxalic acid concentration
should be 0.01 M or less for precipitation of insoluble Fer compounds. In actual
waste extracts, oxalic acid is consumed by calcium present in the wastes, and hence
actual oxalic acid concentrations are lower than those in the original reagents. The
data in Table 29.3 show that Cs removal is possible with 20 times (nominal
concentration ¼ 0.05 M) as well as 10 times (nominal concentration ¼ 0.1 M)
dilutions of 1.0 M oxalic acid extract.
Table 29.3 Removal of cesium (Cs) from the 1 M oxalic acid extract with different dilution factor
applied before ferrocyanide (Fer) coprecipitation (the solution pH was 5 and Fer was 0.1 mM for
all samples)
Sample
code
100 times dilution (~0.01 M
oxalic acid)
20 times dilution
(~0.05 M oxalic acid)
10 times dilution
(~0.1 M oxalic acid)
3
9 7
9 9
9 3
4
9 7
9 5
9 3
5
9 5
9 7
9 6
6
9 8
9 5
9 2
338
Y. Fujikawa et al.