(CN) 6 ], and Ni 2 [Fe(CN) 6 ] are 3.3 Â 10
À41
, 4 Â 10
À16 , 1.3 Â 10
À16 , and 1.3 Â 10
À15 ,
respectively [17]. In the case of Ni 2 [Fe(CN) 6 ], Fer concentration in solution should
be higher than 10
À5 M for insoluble Fer precipitate to be formed. Because the
solubility of fresh metal-Fer compounds can be higher than that of pure compounds,
the minimum Fer concentration used in this study was 10
À4 M.
There are three different ways to use Fer to remove Cs: (1) addition of soluble
Fer salts and metal elements to waste solution (in situ formation of Fer solid),
(2) addition of freshly prepared insoluble Fer-metal complex slurry to waste
solution, and (3) use of Fer-metal adsorbents in solution. The distribution of Cs to
insoluble Fer compounds is highest when the in situ Fer formation method is
applied. If appropriately used, the in situ method is the best for both decontamination and waste volume reduction.
29.3 Experimental
The waste materials, extraction methods, and the corresponding measured metal
concentrations are summarized in Table 29.1. The distilled water extraction technique was used for fly ash samples because it was reported that rad-Cs in fly ash
samples could be extracted with water [18]. Application of a hot oxalic acid (0.1 M)
extraction technique to recover rad-Cs from contaminated sewage sludge in a pilotscale test was reported after the F1 accident [3]. We also tested the method for some
samples in this study.
The distilled water extraction technique (for fly ash samples) and hot oxalic acid
extraction technique (for dewatered sludge and slug samples) were used for waste
samples collected from western Japan unaffected by the F1 accident. Stable
(nonradioactive) Cs or Cs-137 tracer (both contained Cs as Cs
+ ion) was added to
the extracts to estimate Cs removal.
The contaminated fly ash samples from two municipal waste incineration plants
and a sewage treatment plant in the affected area were extracted and analyzed for
rad-Cs in the facilities where they were produced. The sum of Cs-134 and Cs-137
radioactive materials in the fly ash samples K, N, CM and CI (listed in Table 29.1)
were 8 Â 10
4 , 2 Â 10
4 , 9.9 Â 10
4 , and 1.2 Â 10
4 Bq/kg (dry weight basis), respectively. Addition of Cs tracer to the samples was not necessary because it already
contained rad-Cs from the F1 accident, removal of which could be estimated by
radionuclide analysis.
All reagents used in our study were of analytical grade. The sample pH was
adjusted using NaOH and HCl. Potassium ferrocyanide (K 4 [Fe(CN) 6 ], K-Fer hereafter) was used as a soluble Fer salt source. One metal salt of Fe(III)Cl 3, Fe(II)SO 4 ,
NiSO 4 , and ZnSO 4 was added to extract when indigenous metals in it did not
produce insoluble metal-Fer complex. NaCl was used to vary electrolyte concentration of the solutions.
The procedure for extract treatment by Fer precipitation technique was as
follows. Twenty-five milliliters of water extract or 0.5–5 ml of 1 M oxalic acid
334
Y. Fujikawa et al.
À41
, 4 Â 10
À16 , 1.3 Â 10
À16 , and 1.3 Â 10
À15 ,
respectively [17]. In the case of Ni 2 [Fe(CN) 6 ], Fer concentration in solution should
be higher than 10
À5 M for insoluble Fer precipitate to be formed. Because the
solubility of fresh metal-Fer compounds can be higher than that of pure compounds,
the minimum Fer concentration used in this study was 10
À4 M.
There are three different ways to use Fer to remove Cs: (1) addition of soluble
Fer salts and metal elements to waste solution (in situ formation of Fer solid),
(2) addition of freshly prepared insoluble Fer-metal complex slurry to waste
solution, and (3) use of Fer-metal adsorbents in solution. The distribution of Cs to
insoluble Fer compounds is highest when the in situ Fer formation method is
applied. If appropriately used, the in situ method is the best for both decontamination and waste volume reduction.
29.3 Experimental
The waste materials, extraction methods, and the corresponding measured metal
concentrations are summarized in Table 29.1. The distilled water extraction technique was used for fly ash samples because it was reported that rad-Cs in fly ash
samples could be extracted with water [18]. Application of a hot oxalic acid (0.1 M)
extraction technique to recover rad-Cs from contaminated sewage sludge in a pilotscale test was reported after the F1 accident [3]. We also tested the method for some
samples in this study.
The distilled water extraction technique (for fly ash samples) and hot oxalic acid
extraction technique (for dewatered sludge and slug samples) were used for waste
samples collected from western Japan unaffected by the F1 accident. Stable
(nonradioactive) Cs or Cs-137 tracer (both contained Cs as Cs
+ ion) was added to
the extracts to estimate Cs removal.
The contaminated fly ash samples from two municipal waste incineration plants
and a sewage treatment plant in the affected area were extracted and analyzed for
rad-Cs in the facilities where they were produced. The sum of Cs-134 and Cs-137
radioactive materials in the fly ash samples K, N, CM and CI (listed in Table 29.1)
were 8 Â 10
4 , 2 Â 10
4 , 9.9 Â 10
4 , and 1.2 Â 10
4 Bq/kg (dry weight basis), respectively. Addition of Cs tracer to the samples was not necessary because it already
contained rad-Cs from the F1 accident, removal of which could be estimated by
radionuclide analysis.
All reagents used in our study were of analytical grade. The sample pH was
adjusted using NaOH and HCl. Potassium ferrocyanide (K 4 [Fe(CN) 6 ], K-Fer hereafter) was used as a soluble Fer salt source. One metal salt of Fe(III)Cl 3, Fe(II)SO 4 ,
NiSO 4 , and ZnSO 4 was added to extract when indigenous metals in it did not
produce insoluble metal-Fer complex. NaCl was used to vary electrolyte concentration of the solutions.
The procedure for extract treatment by Fer precipitation technique was as
follows. Twenty-five milliliters of water extract or 0.5–5 ml of 1 M oxalic acid
334
Y. Fujikawa et al.