Removal of pertechnetate ion from radioactive waste using anion ...

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124 H. INOUE et al. P is the diffusional membrane permeability, a is the ionic activity, F is the Faraday constant, V0 is the membrane potential at zero membrane current, R is the gas constant, T is the absolute temperature, the superscript I indicates the aqueous solution phase I and the subscripts Na + , − TcO4 , and Cl – refer to co-ion Na + and counter-ions and Cl – TcO4 [8]. The following equation is derived from equation (1): P 0 TcO4 / P 0 Cl 100 10 1 0.1 0 TcO 0 − Cl P P − 4 0 10 20 30 40 50 60 = J a J TcO − 4 − Cl I TcO I − Cl X 10 100 A B 3 X 10 ? 3 a − 4 10 D m TcO4 / D m Cl TcO4 - Radioactivity of phase I / kBq 1 − . (2) 0.1 0 10 20 30 40 50 60 Fig. 3. Membrane permeability ratio 0 0 (A) and diffusion coefficient ratio m m P P D (B) TcO Cl / − − 4 − as a function of TcO radioactivity of phase I. Circles and squares indicate paper membrane 4 and polymer membrane, respectively D − − TcO Cl / 4 On the other hand, the diffusional membrane permeability can be adequately approximated by the diffusion coefficient, i.e. (α = or Cl – m − TcO ), and ion concentration within membrane phase ( C (α = TcO or Cl – Dα m − α 4 )): m m ⎛ D ⎞ ⎡ ⎜ α C ⎟ α ⎜ ⎟ ⎢ I II ⎝ δ ⎠ ⎣( aα aα ) 0 α ≅ 1/ 2 P 4 ⎤ ⎥ , (3) ⎦
Removal of pertechnatate ion 125 where δ is the thickness of the membrane and the m indicates the memrane phase. The diffusional membrane permeability ratio of to Cl – superscript b − 0 0 TcO ( P − P ) was derived from equation (2) and shown in figure 3A. membrane and in the polymer membrane were higher than unity and constant within the whole TcO 4 radioactivity range of the phase I. Although the flux ratio of TcO 4 to –9 J − / J − ranged from approximately 6.3×10 to 2.8× 10 –8 − − for the paper mem- Cl – ( ) Cl TcO 4 4. CONCLUSIONS The anion-exchange paper membrane possesses three outstanding characteristics: (1) higher fluxes of and Cl ymer membrane, (2) almost the sam – − TcO 4 than that of the pol − e occupation of TcO 4 in available ion exchange sites as in the polymer mem- 0 0 brane, and (3) higher diffusional membrane permeability ratio ( P − / P − ) than that 4 TcO / 0 − 4.2×10 influe 3 in the paper membrane and in the polymer membrane, respectively. The diffusional membrane permeability based on the phenomenological equation is effective in expressing the ionic membran sport w ncing the concentration of the − external solution. Actually, it is possible to compare quantitatively the TcO 4 transport with Cl – transport through the membrane by deriving the diffusional membrane per- − meability as shown in figure 3A. The diffusion coefficient ratio of TcO 4 to Cl – e tran ithout m m D − / D − ) was estimated from equations (2) and (3) (figure 3B).The diffusion 4 TcO Cl / − coefficient ratio D − / D − ) was almost the same as the diffusional membrane per- 0 Cl − P P ratios both in the paper brane and 2.4×10 –9 to 1.1×10 –8 for the polymer membrane, the diffusion mbrane perm y ratios of TcO to Cl – 0 0 ( P − / P − ) went in reverse: 1.1×10 4 from al me eabilit and ( TcO 4 Cl tion/membrane distribution of − 4 TcO 4 ( m TcO 4 m Cl 0 0 TcO Cl − TcO 4 to Cl – 4 in the present study. meability ratio ( P − / P − ) as shown in figure 3. This is reflected by not large solu- of the polymer membrane. As a result, TcO transport through the paper membrane is − higher than that through the polymer membrane. TcO 4 flux in t mbrane is higher than that in the polymer memb and TcO 4 can exist in the membrane phase despite the presence of large amount of Cl – he paper me − rane, . − 4 Cl TcO 4 4 Cl
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