Research and Development Relating to the Accident at the TEPCO’s Fukushima Daiichi NPS

1-20 Decontamination of Radioactive Cobalt and Manganese with Radioactive Cesium－ Simplified Treatment Process of Radioactive Liquid Waste by Adding Hexacyanoferrate(ⅠⅠ) Ions －Contaminated water (left) and potassium hexacyanoferrate(ⅠⅠ)
solution (right)

Cloudy solution after adding hexacyanoferrate(ⅠⅠ)
solution to the contaminated water

Solution after reaction

Fig.1-42 Simplified treatment process experiment
Hexacyanoferrate(ⅠⅠ) ions react with transition metal ions, and this reaction produces precipitation of the transition metal
hexacyanoferrate(ⅠⅠ). This precipitation product may selectively adsorb Cs. Therefore, decontamination of both radioactive transition
metals and Cs is expected to be achieved by adding potassium hexacyanoferrate(ⅠⅠ) solution to the contaminated water from 1F.
100Cs removal rate (%)

Removal rate (%)

1007550Mn
Co25NiZｎ80
60
40
2000
0.0

0.5

1.0

1.5

[K4[Fe(CN)6]]/ [transition metals] (in molality)
Fig.1-43 Effect of ratio of hexacyanoferrate/transition metals on
removal rate of transition metals
The removal rates of the transition metals exhibited some differences.
It is possible to remove every radioactive transition metal by adding
a sufficient amount of hexacyanoferrate(ⅠⅠ) ions.

At the TEPCO’s Fukushima Daiichi NPS (1F), an enormousvolume of contaminated water has been generated by reactor
cooling and groundwater inflow, and is temporarily stored
at the site. The contaminated water bears not only fission
products from the spent fuels, such as cesium (Cs), but also
activated corrosion products from the reactor materials, suchas manganese (Mn) and cobalt (Co).
Adsorption with insoluble hexacyanoferrate(ⅠⅠ) is a wellknown method of removing radioactive Cs from liquid waste. For
radioactive Mn and Co decontamination, co-precipitation withiron hydroxide is generally used. In fact, part of the contaminatedwater was actually treated by applying these methods at 1F.
It is known that the insoluble transition metal hexacyanoferrate(ⅠⅠ)
selectively adsorbs Cs among alkaline elements. Hexacyanoferrate(ⅠⅠ)
of Ni, Co, and Fe are typical compounds used to adsorb Cs, andthey are products of the reaction of hexacyanoferrate(ⅠⅠ) ionsand transition metals. In iron co-precipitation, transition metals
are co-precipitated with iron hydroxide, which is a product of
the reaction with iron ions and hydroxide ions, because of theirchemical similarity.
We developed a simplified treatment process for both
radioactive transition metals and Cs decontamination.
Fundamental experiments using both non-radioactive andradioactive solutions were conducted. As shown Fig.1-42,

05101520[transition metal] / [Cs] (in molality)
Fig.1-44 Increase of Cs removal rate
The Cs removal rate increased with[transition metal] / [Cs].

the treatment process consists of two reactions. The first reaction
is in-situ generation of the transition metal hexacyanoferrate(ⅠⅠ)
by adding potassium hexacyanoferrate(ⅠⅠ) solution to thecontaminated water. The second reaction is Cs adsorption on
the first reaction product.
The properties of the in-situ generation of insoluble
hexacyanoferrate(ⅠⅠ) adsorbent were examined using nonradioactive transition metal elements. As shown in Fig.1-43,
the removal rate rose as the ratio [K4[Fe(CN)6]]/[transitionmetal] increased. For [K4[Fe(CN)6]]/[transition metal] > 1, theremoval rates of transition metals were greater than 90%.
The Cs adsorption was also examined to investigate theremoval rate of Cs. As shown in Fig.1-44, the removal rate ofCs was 95% when [transition metal]/[Cs] was 12. The removal
rate of Cs reached 99% when [transition metal]/[Cs] was 18.
These results show that this new treatment process has thepotential to remove both radioactive transition metals andCs effectively when the ratio of Cs and transition metals isappropriate for the reactions.
At 1F, contaminated water has been treated by other treatment
processes. We hope that our proposed process will be applied forthe removal of Cs and transition metals from radioactive liquid
waste in various decontamination processes in and around 1F.

Reference
Takahatake, Y., Shibata, A. et al., Decontamination of Radioactive Liquid Waste with Hexacyanoferrate(II), Procedia Chemistry, vol.7, 2012, p.610-615.
JAEA R&D Review 201331