Abstract
Plutonium(IV) sorption onto quartz in carbonate solutions was systematically investigated under anaerobic conditions to analyze the sorption behaviors of Pu(IV) with a non-electrostatic model (NEM). Pu(IV) sorption data was obtained from batch sorption experiments as a function of pH and carbonate concentration. The Pu(IV) sorption onto quartz showed similar tendencies to Th(IV), which is considered to be chemically analogous as a tetravalent actinoid. The distribution coefficient, Kd, of Pu(IV) onto quartz showed inverse proportionality to the square of the total carbonate concentration under the investigated pH conditions of 8–11. The modeling study, however, revealed a Th(IV) sorption model, which is ≡SOTh(OH)4− and ≡SOThOH(CO3)22−, could not be applied to simulate the Pu(IV) sorption onto quartz. It was inferred that the electrostatic repulsion between negatively charged ligands limited the formation of ≡SOM(OH)4− and ≡SOMOH(CO3)22− for Pu(IV) with smaller ionic radii than Th(IV). The Pu(IV) sorption model was developed as ≡SOPu(OH)3 and ≡SOPu(OH)4−. In addition, data of Pu(IV) sorption onto muscovite was obtained in order to be compared with data for quartz.
Funding source: Nuclear Regulation Authority
Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: Part of this research is funded by the Secretariat of the Nuclear Regulation Authority (NRA), Japan.
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.
Series-1: results for Pu(IV) sorption onto quartz at initial Pu concentration of 4 × 10−11 M, an ionic strength of 0.5 mol/kg, and the solid to liquid ratio (M/Vi) of 25 g/L.
| Total carbonate concentration (M) | pH | Eh (V) | Kd (m3/kg) |
|---|---|---|---|
| 0.05 | 8.54 | −0.12 | (5.6 ± 0.1) × 10−2 |
| 9.12 | 0.32 | (4.7 ± 0.1) × 10−2 | |
| 9.52 | 0.28 | (5.4 ± 0.1) × 10−2 | |
| 9.86 | 0.27 | (8.1 ± 0.2) × 10−2 | |
| 10.2 | 0.24 | (1.4 ± 0.0) × 10−1 | |
| 10.8 | 0.17 | (6.1 ± 0.3) × 10−1 | |
| 0.1 | 8.60 | −0.11 | (1.1 ± 0.0) × 10−2 |
| 9.20 | 0.30 | (1.4 ± 0.0) × 10−2 | |
| 9.59 | 0.26 | (2.1 ± 0.1) × 10−2 | |
| 9.75 | 0.23 | (2.1 ± 0.1) × 10−2 | |
| 9.91 | 0.20 | (2.2 ± 0.1) × 10−2 | |
| 10.3 | 0.16 | (4.0 ± 0.1) × 10−2 | |
| 11.0 | −0.19 | (2.6 ± 0.1) × 10−1 | |
| 0.3 | 8.61 | −0.11 | (8.6 ± 2.6) × 10−4 |
| 8.77 | −0.05 | (8.4 ± 3.2) × 10−4 | |
| 9.01 | −0.11 | (8.8 ± 3.2) × 10−4 | |
| 9.09 | −0.14 | (3.8 ± 3.1) × 10−4 | |
| 9.18 | −0.18 | (9.3 ± 3.2) × 10−4 | |
| 9.35 | −0.22 | (6.3 ± 3.2) × 10-4 | |
| 9.50 | −0.13 | (1.5 ± 0.3) × 10−3 |
Series-2: results for Pu(IV) sorption onto quartz at pH 9 and an ionic strength of 1.0 mol/kg. M/Vi is the solid to liquid ratio.
| Total carbonate concentration (M) | Initial Pu concentration (M) | M/Vi (g/L) | pH | Eh (V) | Kd (m3/kg) |
|---|---|---|---|---|---|
| 10−3 | 2 × 10−11 | 0.25 | 8.68 | 0.18 | (2.0 ± 0.1) × 101 |
| 10−2.5 | 2 × 10−11 | 0.25 | 8.89 | 0.17 | (9.7 ± 0.3) × 100 |
| 10−2 | 2 × 10−11 | 0.25 | 8.96 | 0.17 | (3.2 ± 0.1) × 100 |
| 4 × 10−11 | 25 | 8.91 | 0.16 | (1.6 ± 0.2) × 100 | |
| 10−1.5 | 2 × 10−11 | 0.25 | 9.01 | 0.15 | (2.0 ± 0.4) × 10−1 |
| 4 × 10−11 | 25 | 8.99 | 0.14 | (1.3 ± 0.0) × 10−1 | |
| 10−1 | 4 × 10−11 | 25 | 9.19 | 0.13 | (7.6 ± 0.3) × 10−3 |
| 10−0.5 | 4 × 10−11 | 25 | 9.25 | 0.13 | <4.0 × 10−4 |
Series-3: results for Pu(IV) sorption onto muscovite at initial Pu concentration of 4 × 10−11 M, an ionic strength of 0.5 mol/kg, and the solid to liquid ratio (M/Vi) of 25 g/L.
| Total carbonate concentration (M) | pH | Eh (V) | Kd (m3/kg) |
|---|---|---|---|
| 0.1 | 8.53 | 0.04 | (6.5 ± 0.4) × 10−3 |
| 9.15 | 0.40 | (5.3 ± 0.5) × 10−3 | |
| 9.54 | 0.34 | (4.5 ± 0.5) × 10−3 | |
| 9.72 | 0.01 | (4.8 ± 0.5) × 10−3 | |
| 9.88 | 0.30 | (5.5 ± 0.5) × 10−3 | |
| 10.3 | 0.18 | (1.3 ± 0.1) × 10−2 | |
| 11.0 | −0.04 | (2.2 ± 0.1) × 10−1 | |
| 0.3 | 8.59 | 0.04 | (1.4 ± 0.3) × 10−3 |
| 9.11 | −0.03 | (7.2 ± 4.2) × 10−4 | |
| 9.50 | 0.03 | (7.5 ± 3.3) × 10−4 |
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