Ⅲ-3. Radiochemistry & Nuclear Chemistry

RIKEN Accel. Prog. Rep. 53

Separation of 121m Te from antimony without redox reaction
T. Kubota,∗1,∗2 S. Fukutani,∗1 T. Takahashi,∗1 H. Haba,∗2 D. Mori,∗2 and S. Takahashi∗1
Radioactive tellurium isotopes, such as 129 Te, 131 Te,
and 132 Te, were released in the Fukushima Dai-ichi
nuclear accident and are regarded as signiﬁcant for
the evaluation of exposure dose during 2011. Owing
to their short half-life, radioactive materials derived
from the accident have already decayed out; thus, theevaluation requires some laboratory experiments. In
experiments where radio nuclides are added to plant
and animal samples, carrier-free and high-purity tracers should be employed to avoid undesirable chemical
eﬀects. The production of a suitable tracer had been
investigated in previous reports where radioactive tellurium generated by the bombardment of Sb2 O3 with
deuteron at an energy of 24 MeV was puriﬁed througha redox reaction.1,2) However, this method generates
toxic chlorine gas. More moderate methods, therefore,should be developed.
We found that tellurium is separated as a cationfrom anionic antimony through anion exchange chromatography. Chemical species of both elements werecalculated under several conditions, following which
tellurium was separated using the calculation results.
Tellurium and antimony exist as chloro-complex anions in a high-concentration HCl solution. With increasing pH, Te(IV) is converted into TeOOH+ , while
Sb(III) forms a precipitate. Through this precipitation, a large part of tellurium is co-precipitated. We
considered that tellurium can be puriﬁed with carefulcontrol of the pH and HCl concentration, and we investigated the optimal conditions using Medusa-Hydrachemical equilibrium software for Windows.3) The calculation results are shown below. Te(IV) was converted into TeOOH+ at pH > −0.2 and [HCl] < 1.6 M.
Sb(III) remained as a solution at pH < −0.5 and [HCl]> 3.2 M with [Sb] = 200 mM, which is equivalent to
900 mg Sb2 O3 dissolved in 30 mL HCl and to a concentration derived from ordinary production at one time.
At this antimony concentration, tellurium cannot bepuriﬁed. Based on the fact that the solubility of antimony depends on its concentration, the maximum concentration of antimony at pH = −0.2 without precipitation was calculated to be 7 mM. In order to ensurethat the puriﬁcation was conducted without precipitation, we applied a concentration of 5 mM Sb.
An irradiated Sb2 O3 pellet was dissolved in concentrated HCl, following which insoluble antimony was removed by centrifugation. The supernatant was diluted
with H2 O to 2.4 M HCl and 5 mM Sb solution. The solution was loaded onto anion exchange resin (AG1x8,∗1∗2Institute for Integrated Radiation and Nuclear Science, Kyoto University
RIKEN Nishina Center- 195 -Fig. 1. Elution (□) and total recovery ratio (⃝) of tellurium from antimony (5 mM) with 1.6 M HCl.

Cl-form, 100–200 mesh, 10 mL), following which Te121m was eluted with 1.6 M HCl.
Figure 1 shows the elution curve of Te-121m and thetotal recovery ratio of Te-121m. The total recovery
ratio of Te-121m reached almost 100% with ﬁve bed
volume eluent, while antimony was adsorbed onto theanion exchange resin without elution.
In this research, we investigated the puriﬁcation oftellurium from matrix antimony with pH regulation.
Its performance was satisfactory for a low antimony
concentration. Further investigations are required tooptimize the separation method for higher concentrations.
References

1) T. Kubota et al., RIKEN Accel. Prog. Rep. 50, 254(2017).
2) T. Kubota et al., RIKEN Accel. Prog. Rep. 52, 205(2019).
3) I. Puigdomenech, Chemical equilibrium diagrams:
MEDUSA, (2010), https://www.kth.se/che/medusa/
downloads-1.386254 (accessed 2020-07-20).