Review of Thermodynamic Sorption Model for Radionuclides on Bentonite Clay

Jeonghwan Hwang; Jung-Woo Kim; Weon Shik Han; Won Woo Yoon; Jiyong Lee; Seonggyu Choi

doi:10.9719/EEG.2023.56.5.515

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Econ. Environ. Geol. 2023; 56(5): 515-532

Published online October 30, 2023

https://doi.org/10.9719/EEG.2023.56.5.515

Review of Thermodynamic Sorption Model for Radionuclides on Bentonite Clay

Jeonghwan Hwang^1,*, Jung-Woo Kim¹, Weon Shik Han², Won Woo Yoon², Jiyong Lee², Seonggyu Choi³

Author Info. +

¹Disposal Safety Evaluation Research Division, Korea Atomic Energy Research Institute (KAERI)
²Department of Earth System Sciences, Yonsei University
³Disposal Performance Demonstration R&D Division, Korea Atomic Energy Research Institute (KAERI)

Correspondence to : ^*hwangjh@kaeri.re.kr

Received: September 22, 2023; Revised: October 13, 2023; Accepted: October 16, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

Bentonite, predominantly consists of expandable clay minerals, is considered to be the suitable buffering material in high-level radioactive waste disposal repository due to its large swelling property and low permeability. Additionally, the bentonite has large cation exchange capacity and specific surface area, and thus, it effectively retards the transport of leaked radionuclides to surrounding environments. This study aims to review the thermodynamic sorption models for four radionuclides (U, Am, Se, and Eu) and eight bentonites. Then, the thermodynamic sorption models and optimized sorption parameters were precisely analyzed by considering the experimental conditions in previous study. Here, the optimized sorption parameters showed that thermodynamic sorption models were related to experimental conditions such as types and concentrations of radionuclides, ionic strength, major competing cation, temperature, solid-to-liquid ratio, carbonate species, and mineralogical properties of bentonite. These results implied that the thermodynamic sorption models suggested by the optimization at specific experimental conditions had large uncertainty for application to various environmental conditions.

Keywords bentonite, radionuclide, thermodynamic sorption model, deep geological disposal repository, engineered barrier system

벤토나이트와 방사성 핵종의 열역학적 수착 모델 연구

황정환^1,* · 김정우¹ · 한원식² · 윤원우² · 이지용² · 최승규³

¹한국원자력연구원 저장처분기술개발부
²연세대학교 지구시스템과학과
³한국원자력연구원 저장처분성능검증부

요 약

벤토나이트는 고준위 방사성폐기물 처분을 위한 심층처분 시스템에서 처분용기와 암반 사이를 메우는 완충재로 고려되는 팽창성 점토이다. 벤토나이트는 높은 양이온교환능과 비표면적을 가지고 있기 때문에, 처분용기로부터 핵종이 누출될 경우, 수착하여 암반으로의 유출을 지연시키는 역할을 한다. 본 연구에서는 여러 선행연구에서 8종류의 벤토나이트를 사용하여 수행된 U, Am, Se, Eu 핵종의 수착실험 및 모델 자료를 취합하고, 각 연구에서 설정된 실험 조건들을 기반으로 열역학적 수착모델의 특성을 평가하였다. 핵종과 벤토나이트 간의 수착 거동 해석에 중요한 역할을 하는 열역학적 수착모델은 벤토나이트의 광물학적 특성뿐만 아니라 핵종 농도, 용액의 이온강도, 주 양이온, 온도, 고액비, 용존 탄산 농도 등 세부적인 실험 조건과 밀접하게 연관되어 있는 것으로 확인되었다. 이러한 결과는 특정 실험 조건에서 수행된 수착실험 및 모델의 최적화로 제안되는 수착 반응식과 반응상수가 다양한 환경 조건에 적용하기에 불확실성이 크다는 것을 의미한다. 따라서, 심층처분 시스템에 적용가능한 열역학적 수착모델을 구축하기 위해서는 현장 조사 및 실험이 함께 수행되어야 한다.

주요어 벤토나이트, 방사성핵종, 열역학적 수착모델, 심층처분 시설, 공학적방벽

Article

Special Review on “Geological and Environmental Sciences for Sustainable Nuclear Energy”

Econ. Environ. Geol. 2023; 56(5): 515-532

Published online October 30, 2023 https://doi.org/10.9719/EEG.2023.56.5.515

Review of Thermodynamic Sorption Model for Radionuclides on Bentonite Clay

Jeonghwan Hwang^1,*, Jung-Woo Kim¹, Weon Shik Han², Won Woo Yoon², Jiyong Lee², Seonggyu Choi³

Correspondence to:^*hwangjh@kaeri.re.kr

Received: September 22, 2023; Revised: October 13, 2023; Accepted: October 16, 2023

Abstract

Keywords bentonite, radionuclide, thermodynamic sorption model, deep geological disposal repository, engineered barrier system

벤토나이트와 방사성 핵종의 열역학적 수착 모델 연구

황정환^1,* · 김정우¹ · 한원식² · 윤원우² · 이지용² · 최승규³

¹한국원자력연구원 저장처분기술개발부
²연세대학교 지구시스템과학과
³한국원자력연구원 저장처분성능검증부

Received: September 22, 2023; Revised: October 13, 2023; Accepted: October 16, 2023

요 약

주요어 벤토나이트, 방사성핵종, 열역학적 수착모델, 심층처분 시설, 공학적방벽

Table 1

List of previous studies, together with utilized bentonite samples, sorption models, and target radionuclides.

No	Reference	Bentonite	Sorption Model	Radionuclides
1	Bradbury and Baeyens (2002)	SWy-1	2SP-NE-SC/CE	Eu
2	Bradbury and Baeyens (2005)	SWy-1	2SP-NE-SC/CE	U, Am, Eu
3	Bradbury and Baeyens (2006)	SWy-1	2SP-NE-SC/CE	Am, Eu
4	Fernandes et al. (2008)	SWy-1	2SP-NE-SC/CE	Eu
5	Fernandes et al. (2012)	SWy-1	2SP-NE-SC/CE	U
6	Schnurr et al. (2015)	SWy-1	2SP-NE-SC/CE	Eu
7	Kowal-Fouchard et al. (2004)	Volclay	2SP-CC-SC/CE	U
8	Bradbury and Baeyens (2011)	MX-80	2SP-NE-SC/CE	U, Eu
9	Tertre et al. (2006)	MX-80	2SP-DL-SC/CE	Eu
10	Yang et al. (2010)	Jinchuan	2SP-DL-SC/CE	U
11	Guo et al. (2009)	Jinchuan	2SP-DL-SC/CE	Eu
12	Missana et al. (2021)	FEBEX	2SP-NE-SC/CE	Eu
13	Missana et al. (2009)	FEBEX	2SP-NE-SC/CE	Se
14	Kumar et al. (2013)	Western India	2SP-NE-SC/CE	Am, Eu
15	Gao et al. (2021)	GMZ	2SP-NE-SC/CE	Am
16	Shi et al. (2014)	GMZ	2SP-DL-SC/CE	Se, Eu
17	Pablan and Turner (1996)	SAz-1	2SP-DL-SC/CE	U

Table 2 -1

List of bentonite samples considered in this study, together with the experimental conditions used in reference studies from 1–10 (details were provided in Table 1). [R]_initial represented the concentration of radionuclides, Major Cat. represented the predominant cations, S:L Ratio represented for the solid to liquid ratio, and [CO₃]_total represented the carbonate concentration.

Bentonite [Ref]	Radio nuclide	[R]_initial (mol L^–1)	pH	Temp (℃)	Major Cat.	Ionic Strength (mol L^–1)	S:L Ratio (g L^–1)	[CO₃]_total (mol L^–1)
SWy-1 [1]	Eu	9.5×10–⁹	3–10	25	Ca	0.066	1	-
		10–⁹–10–³	6.9	25	Ca	0.066	1	-
		10–⁹–10–³	6.0	25	Ca	0.066	1	-
		1.3×10–⁷	4–9	25	Na⁺	0.1	1.5	-
		10–⁹–10–³	6.0, 7.2	25	Na⁺	0.1	0.5	-
		10–⁹–10–³	6.0	25	Na⁺	0.1	0.5	-
SWy-1 [2]	U	1.4×10–⁷	3–10	25	Na⁺	0.01	1.2	-
	U	1.4×10–⁷	3–10	25	Na⁺	0.1	1.2	-
	Am	3×10–⁸	3–10	25	Na⁺	0.1	4	-
	Am	3×10–⁸	3–10	25	Na⁺	1	4	-
	Eu	1.3×10–⁷	3–10	25	Na⁺	0.1	1.5	-
	Eu	9.5×10–⁹	4–9	25	Ca	0.066	1	-
SWy-1 [3]	Am	1.5×10–¹⁰	3–10	25	Na⁺	0.1	0.62	-
SWy-1 [3]	Am	6.2×10–⁸	3–9	25	Ca	0.066	0.86–2	-
SWy-1 [4]	Eu	2×10–⁹	4–9	25	Na⁺	0.1	1	-
		2×10–⁹	6–10	25	Na⁺	0.1	1	10–^3.5 atm
		2×10–⁹	7–9	25	Na⁺	0.1	1	2×10–²
SWy-1 [5]	U	10–⁷	3–9	25	Na⁺	0.1	0.9	-
		10–⁷	4–10	25	Na⁺	0.1	2.5	10–^3.5 atm
		10–⁷	7–9	25	Na⁺	0.1	4.3	10–³, 3×10–³, 5×10–³
		10–⁸–10–⁴	5, 6.8, 8	25	Na⁺	0.1	0.9	-
		10–⁸–10–⁴	5, 6.8, 8	25	Na⁺	0.1	1.5	10–^3.5 atm
SWy-1 [6]	Eu	2×10–⁷	3–12	25	Na⁺	0.1	2	-
		2×10–⁷	3–12	25	Na⁺	0.9	2	-
		2×10–⁷	3–12	25	Na⁺	3.9	2	-
Volclay [7]	U	10–⁶	2–7	25	Na⁺	0.1	10	-
		10–³	2–7	25	Na⁺	0.5	10	-
		10–⁴	2–7	25	Na⁺	0.1, 0.5	10	-
MX-80 [8]	U	3×10–⁸–10–⁶	7.6	25	Na⁺	0.6	0.32–13.5	-
MX-80 [8]	Eu	3.2×10–¹¹–1.6×10–⁶	7.5	25	Na⁺	0.6	1.56	-
MX-80 [9]	Eu	10–⁶	3–10	25	Na⁺	0.5	2.5	-
		10–⁶	4–8	40	Na⁺	0.5	2.5	-
		10–⁶	2–7	80	Na⁺	0.5	2.5	-
		10–⁶	2–4	150	Na⁺	0.5	2.5	-
Jinchuan [10]	U	8×10–⁵	3–10	25	Na⁺	0.1	1	-
		4×10–⁵	4–10	25	Na⁺	0.1	1	-
		10–⁵–10–³	4.8	25	Na⁺	0.1	1	-
		10–⁵–10–³	5.8	25	Na⁺	0.1	1	-
		8×10–⁵	5	25	Na⁺	0.1	0.1–5	-
		8×10–⁵	3–10	25	Na⁺	0.1	1	10–^3.58 atm
		8×10–⁵	3–10	60	Na⁺	0.1	1	-
		8×10–⁵	3–7	80	Na⁺	0.1	1	-

Table 2-2

List of bentonite samples considered in this study, together with the experimental conditions used in reference studies from 11–17 (details were provided in Table 1). [R]_initial represented the concentration of radionuclides, Major Cat. represented the predominant cations, S:L Ratio represented for the solid to liquid ratio, and [CO₃]_total represented the carbonate concentration.

Bentonite [Ref]	Radio nuclide	[R]_initial (mol L^–1)	pH	Temp (℃)	Major Cat.	Ionic Strength (mol L^–1)	S:L Ratio (g L^–1)	[CO₃]_total (mol L^–1)
Jinchuan [11]	Eu	6.7×10–⁸	2–10	25	Na⁺	0.1	0.5	-
		3.3×10–⁶	2–10	25	Na⁺	0.1	0.5	-
		6.7×10–⁸	3–10	25	Na⁺	0.1	0.5	10–^3.58 atm
		3.8×10–⁷	3–10	25	Na⁺	0.1	0.5	10–^3.58 atm
		3.3×10–⁶	3–10	25	Na⁺	0.1	0.5	10–^3.58 atm
		10–⁹–10–³	4, 6	25	Na⁺	0.1	1	-
		10–⁹–10–³	6.5	25	Na⁺	0.1	0.5	-
		10–⁹–10–³	7.5	25	Na⁺	0.1	0.25	-
FEBEX [12]	Eu	10–⁸	3–11	25	Na⁺	0.001–0.2	0.5	-
		10–⁸–10–³	4.1	25	Na⁺	0.2	0.5	-
		10–⁹–10–³	3.8	25	Na⁺	0.1	0.5	-
		10–⁹–10–³	3.9	25	Na⁺	0.05	0.5	-
FEBEX [13]	Se	4×10–¹⁰	3–11	25	Na⁺	0.001–0.5	0.5	-
		10–¹⁰–10–⁴	4.3	25	Na⁺	0.1, 0.5	0.5–1	-
		10–¹⁰–10–⁴	7.2	25	Na⁺	0.01	0.5–1	-
Western India [14]	Am	6×10–⁹	2–10	25	Na⁺	0.1	0.5	-
		6×10–⁹	2–10	25	Na⁺	0.05	0.5	-
		6×10–⁹	2–10	25	Na⁺	0.01	0.5	-
		6×10–⁹	2–10	25	Ca	0.034	0.5	-
	Eu	10–⁷–10–³	6.0	25	Na⁺	0.1	0.5	-
GMZ [15]	Am	6×10–¹⁰	3–10	25, 50, 80	Na⁺	0.1	0.5	-
		6×10–¹⁰	3–10	25	Ca	0.1	0.5	-
		6×10–¹⁰	4.1, 6.6	25	Na⁺	0−0.3	0.5	-
		10–¹⁰–10–⁸	4.0	25	Na⁺	0.1	0.5	-
		10–¹¹–10–⁹	6.5	25	Na⁺	0.1	0.5	-
		10–¹⁰–10–⁸	3.7	25	Ca	0.1	0.5	-
GMZ [16]	Se	1.2×10–⁵	3–9	25	Na⁺	0.1	20	-
	Se	10–⁶–10–³	4.1	25	Na⁺	0.1	20	-
	Eu	3.3×10–⁵	4–9	25	Na⁺	0.1	1	-
	Se	1.2×10–⁵	3–9	25	Na⁺	0.1	20	-
	Eu	3.3×10–⁵	3–9	25	Na⁺	0.1	20	-
	Se	3.3×10–⁵	4–9	25	Na⁺	0.1	1	-
	Eu	3.3×10–⁵	4–9	25	Na⁺	0.1	1	-
	Se	3.3×10–³	4–9	25	Na⁺	0.1	1	-
	Eu	3.3×10–⁵	4–9	25	Na⁺	0.1	1	-
SAz-1 [17]	U	2×10–⁷	2–9	25	Na⁺	0.1	0.03–3	10–^3.5 atm
SAz-1 [17]	U	2×10–⁶	2–9	25	Na⁺	0.1	0.3	10–^3.5 atm

Table 3

Summary of the site types, site capacities of sorption models for various bentonite samples. Here, S^s-OH, S^w1-OH, S^w2-OH, Al-OH, Si-OH, S^w-OH, S-OH, and Y-OH represented surface complexation sites, and X represented cation exchange sites.

Bentonite	Sorption Model	Site Types	Site Capacities	Reference
SWy-1	2SP-NE-SC/CE	S^s-OH	2.0 × 10⁻³ mol kg⁻¹	1–6
		S^{w1, w2}-OH	4.0 × 10⁻² mol kg⁻¹
		X	0.87 eq kg⁻¹
Volclay	2SP-CC-SC/CE	Al-OH	1.75 × 10⁻² mol kg⁻¹	7
		Si-OH	2.5 × 10−¹ mol kg⁻¹
		X	5.75 × 10−¹ mol kg⁻¹
MX-80	2SP-NE-SC/CE	S^s-OH	2.0 × 10⁻³ mol kg⁻¹	8
		S^{w1, w2}-OH	4.0 × 10⁻² mol kg⁻¹
		X	0.787 eq kg⁻¹
	2SP-DL-SC/CE	Al-OH	1.7 × 10⁻³ mol m−2	9
		Si-OH	3.4 × 10⁻³ mol m−2
		X	3.63 × 10−⁵ mol m−2
Jinchuan	2SP-DL-SC/CE	S-OH	5.88 × 10−⁷ mol m−2	10
		Y-OH	1.18 × 10−⁶ mol m−2
		X	1.16 × 10−⁵ mol m−2
	2SP-DL-SC/CE	S^s-OH	1.88 × 10−⁸ mol m−2	11
		S^w-OH	5.69 × 10−⁷ mol m−2
		Y-OH	1.18 × 10−⁶ mol m−2
		X	1.16 × 10−⁵ mol m−2
FEBEX	2SP-NE-SC/CE	S^s-OH	2.01 × 10⁻³ mol kg⁻¹	12
		S^w-OH	6.01 × 10⁻² mol kg⁻¹
		X	1.02 eq kg⁻¹
	2SP-NE-SC/CE	S^s-OH	2.01 × 10⁻³ mol kg⁻¹	13
	2SP-NE-SC/CE	S^w-OH	6.01 × 10⁻² mol kg⁻¹	13
Western India	2SP-NE-SC/CE	S^s-OH	1.8 × 10⁻³ mol kg⁻¹	14
		S^w-OH	3.6 × 10⁻² mol kg⁻¹
		X	0.76 eq kg⁻¹
GMZ	2SP-NE-SC/CE	S^s-OH	1.04 × 10−⁸ mol m−2	15
		S^w-OH	1.03 × 10−⁶ mol m−2
		Y-OH	2.08 × 10−⁶ mol m−2
		X	1.35 × 10−⁵ mol m−2
	2SP-DL-SC/CE	S-OH	9.39 × 10−⁷ mol m−2	16
		Y-OH	1.18 × 10−⁶ mol m−2
		X	1.35 × 10−⁵ mol m−2
SAz-1	2SP-DL-SC/CE	Al-OH	4.73 × 10−⁵ mol L⁻¹	17
SAz-1	2SP-DL-SC/CE	Si-OH	5.69 × 10−⁵ mol L⁻¹	17

Table 4

Summary of the protolysis reactions and their constants of sorption models for various bentonite samples. Here, S^s-OH, S^w1-OH, S^w2-OH, Al-OH, Si-OH, S^w-OH, S-OH, and Y-OH represented surface complexation sites, respectively.

Bentonite	Sorption Model	Protolysis Reactions	log Ksite
SWy-1	2SP-NE-SC/CE	S^s/w1-OH + H⁺ ↔ S^s/w1-OH₂⁺	4.5
		S^s/w1-OH ↔ S^s/w1-O⁻ + H⁺	−7.9
		S^w2-OH + H⁺ ↔ S^w2-OH₂⁺	6.0
		S^w2-OH ↔ S^w2-O⁻ + H⁺	−10.5
Volclay	2SP-CC-SC/CE	Al-OH + H⁺ ↔ Al-OH₂⁺	7.9
		Al-OH ↔ Al-O⁻ + H⁺	−9.4
		Si-OH ↔ Si-O⁻ + H⁺	−7.8
MX-80	2SP-NE-SC/CE	S^s/w1-OH + H⁺ ↔ S^s/w1-OH₂⁺	4.5
		S^s/w1-OH ↔ S^s/w1-O⁻ + H⁺	−7.9
		S^w2-OH + H⁺ ↔ S^w2-OH₂⁺	6.0
		S^w2-OH ↔ S^w2-O⁻ + H⁺	−10.5
	2SP-DL-SC/CE	Al-OH + H⁺ ↔ Al-OH₂⁺	5.1
		Al-OH ↔ Al-O⁻ + H⁺	−8.5
		Si-OH ↔ Si-O⁻ + H⁺	−7.9
Jinchuan	2SP-DL-SC/CE	S-OH + H⁺ ↔ S-OH₂⁺	3.23
		S-OH ↔ S-O⁻ + H⁺	−3.89
		Y-OH ↔ Y-O⁻ + H⁺	−6.57
	2SP-DL-SC/CE	S^{s, w}-OH + H⁺ ↔ S^{s, w}-OH₂⁺	3.23
		S^{s, w}-OH ↔ S^{s, w}-O⁻ + H⁺	−3.89
		Y-OH ↔ Y-O⁻ + H⁺	−6.57
FEBEX	2SP-NE-SC/CE	S^s-OH + H⁺ ↔ S^s-OH₂⁺	4.8
		S^s-OH ↔ S^s-O⁻ + H⁺	−9.9
		S^w-OH + H⁺ ↔ S^w-OH₂⁺	5.3
		S^w-OH ↔ S^w-O⁻ + H⁺	−8.4
Western India	2SP-NE-SC/CE	S^s-OH + H⁺ ↔ S^s-OH₂⁺	4.5
		S^s-OH ↔ S^s-O⁻ + H⁺	−7.9
		S^w-OH + H⁺ ↔ S^w-OH₂⁺	4.5
		S^w-OH ↔ S^w-O⁻ + H⁺	−7.9
GMZ	2SP-NE-SC/CE	S^{s, w}-OH + H⁺ ↔ S^{s, w}-OH₂⁺	5.83
		S^{s, w}-OH ↔ S^{s, w}-O⁻ + H⁺	−7.02
		Y-OH ↔ Y-O⁻ + H⁺	−8.75
	2SP-DL-SC/CE	S-OH + H⁺ ↔ S-OH₂⁺	6.15
		S-OH ↔ S-O⁻ + H⁺	−9.27
		Y-OH ↔ Y-O⁻ + H⁺	−9.06
SAz-1	2SP-DL-SC/CE	Al-OH + H⁺ ↔ Al-OH₂⁺	8.33
		Al-OH ↔ Al-O⁻ + H⁺	−9.73
		Si-OH ↔ Si-O⁻ + H⁺	−7.20

Table 5

Surface complexation constants and selectivity coefficients on surface complexation sites (S^s-OH, S^w1-OH, Al-OH, Si-OH) and cation exchange sites (X) for uranium (U) sorption on various bentonites.

Surface complexation / Cation exchange reaction	log K
SWy-1 + 2SP-NE-SC/CE
S^s-OH + UO₂²⁺ ↔ S^s-OUO₂+ + H⁺	3.1^a,b
S^s-OH + UO₂²⁺ + H₂O ↔ S^s-OUO₂OH + 2H⁺	−3.4^a, −4.6^b
S^s-OH + UO₂²⁺ + 2H₂O ↔ S^s-OUO₂(OH)₂⁻ + 3H⁺	−11^a, −12.6^b
S^s-OH + UO₂²⁺ + 3H₂O ↔ S^s-OUO₂(OH)₃²⁻ + 4H⁺	−20.5^a, −20.9^b
S^s-OH + UO₂²⁺ + CO₃²⁻ ↔ S^s-OUO₂CO₃⁻ + H⁺	9.8^b
S^s-OH + UO₂²⁺ + 2CO₃²⁻ ↔ S^s-OUO₂(CO₃)₂³⁻ + H⁺	15.5^b
S^w1-OH + UO₂²⁺ ↔ S^w1-OUO₂+ + H⁺	0.7^a, 0.5^b
S^w1-OH + UO₂²⁺ + H₂O ↔ S^w1-OUO₂OH + 2H⁺	−5.7^a,b
S^w1-OH + UO₂²⁺ + CO₃²⁻ ↔ S^w1-OUO₂CO₃⁻ + H⁺	9.3^b
2Na-X + UO₂²⁺ ↔ UO₂-X₂ + 2Na⁺	0.7^a, 1.4^a, 0.45^b
MX-80 + 2SP-NE-SC/CE
S^s-OH + UO₂²⁺ ↔ S^s-OUO₂+ + H⁺	3.1^c
S^s-OH + UO₂²⁺ + H₂O ↔ S^s-OUO₂OH + 2H⁺	−3.4^c
S^s-OH + UO₂²⁺ + 2H₂O ↔ S^s-OUO₂(OH)₂⁻ + 3H⁺	−11^c
S^s-OH + UO₂²⁺ + 3H₂O ↔ S^s-OUO₂(OH)₃²⁻ + 4H⁺	−20.5^c
S^w1-OH + UO₂²⁺ ↔ S^w1-OUO₂+ + H⁺	0.7^c
S^w1-OH + UO₂²⁺ + H₂O ↔ S^w1-OUO₂OH + 2H⁺	−5.7^c
S^w1-OH + UO₂²⁺ + CO₃²⁻ ↔ S^w1-OUO₂CO₃⁻ + H⁺	9.3^c
2Na-X + UO₂²⁺ ↔ UO₂-X₂ + 2Na⁺	0.15^c
Volclay + 2SP-CC-SC/CE
Al-(OH)2 + UO₂²⁺ ↔ Al-(OH)2UO₂²⁺	14.9^d
Si-(OH)2 + UO₂²⁺ ↔ Si-O₂UO₂ + 2H⁺	−3.8^d
Si-(OH)2 + 3UO₂²⁺ + 5H₂O ↔ Si-O₂(UO₂)3(OH)5− + 7H⁺	−20.0^d
2Na-X + UO₂²⁺ ↔ UO₂-X₂ + 2Na⁺	3.0^d
SAz-1 + 2SP-DL-SC/CE
Al-OH + UO₂²⁺ ↔ Al-OUO₂+ + H⁺	2.7^e
Al-OH + 3UO₂²⁺ + 5H₂O ↔ Al-O(UO₂)3(OH)5 + 6H⁺	−14.95^e
Si-OH + UO₂²⁺ ↔ Si-OUO₂+ + H⁺	2.6^e
Si-OH + 3UO₂²⁺ + 5H₂O ↔ Si-O(UO₂)3(OH)5 + 6H⁺	−15.29^e

^aBradbury and Baeyens, 2005.

^bFernandes et al., 2012.

^cBradbury and Baeyens, 2011.

^dKowal-Fouchard et al., 2004.

^ePabalan and Turner, 1996.

Table 6

Surface complexation constants and selectivity coefficients on surface complexation site (S-OH) and cation exchange site (X) for uranium (U) sorption on Jinchuan bentonite at elevated temperature condition (Yang et al., 2010).

Surface complexation / Cation exchange reaction	log K
Jinchuan + 2SP-DL-SC/CE
S-OH + UO₂²⁺ ↔ S-OUO₂+ + H⁺	−0.9^a, 0.1^b, 0.5^c
S-OH + 3UO₂²⁺ + 5H₂O ↔ S-O(UO₂)3(OH)5 + 6H⁺	−15.7^a, −13.1^b, −11.3^c
S-OH + 3UO₂²⁺ + 7H₂O ↔ S-O(UO₂)3(OH)72− + 8H⁺	−26.2^a, −23.0^b, −21.0^c
2Na-X + UO₂²⁺ ↔ UO₂-X₂ + 2Na⁺	0.6^{a, b, c}

^aT = 25℃.

^bT = 60℃.

^cT = 80℃.

Table 7

Surface complexation constants and selectivity coefficients on surface complexation sites (S^s-OH, S^w-OH) and cation exchange sites (X) for americium (Am) sorption on various bentonite samples.

Surface complexation / Cation exchange reaction	log K
SWy-1 + 2SP-NE-SC/CE
S^s-OH + Am3+ ↔ S^s-OAm2+ + H⁺	1.6^a,b
S^s-OH + Am3+ + H₂O ↔ S^s-OAmOH⁺ + 2H⁺	−6.8^a,b
S^s-OH + Am3+ + 2H₂O ↔ S^s-OAm(OH)2 + 3H⁺	−15^a, −14.8^b
S^s-OH + Am3+ + 3H₂O ↔ S^s-OAm(OH)3− + 4H⁺	−25.6^a
3Na-X + Am3+ ↔ Am-X₃ + 3Na⁺	1.67^a, 1.46^b
3Ca-X₂ + 2Am3+ ↔ 2Am-X₃ + 3Ca2+	1.66^b
GMZ + 2SP-NE-SC/CE
S^s-OH + Am3+ ↔ SsO-Am2+ + H⁺	2.7^c
S^s-OH + Am3+ + H₂O ↔ S^s-OAmOH⁺ + 2H⁺	−5.5^c
S^s-OH + Am3+ + 2H₂O ↔ S^s-OAm(OH)2 + 3H⁺	−13.5^c
S^s-OH + Am3+ + 3H₂O ↔ S^s-OAm(OH)3− + 4H⁺	−25.1^c
3Na-X + Am3+ ↔ Am-X₃ + 3Na⁺	2.0^c
Na-X + 0.5Ca2+ ↔ Ca0.5-X + Na⁺	0.4^c
Western India + 2SP-NE-SC/CE
S^s-OH + Am3+ ↔ S^s-O Am2+ + H⁺	1.87^d
S^s-OH + Am3+ + H₂O ↔ S^s-OAmOH⁺ + 2H⁺	−5.4^d
S^s-OH + Am 3+ + 2H₂O ↔ S^s-OAm(OH)2 + 3H⁺	−20.2^d
S^w-OH + Am 3+ ↔ S^w-OAm2+ + H⁺	−0.3^d
3Na-X + Am3+ ↔ Am-X₃ + 3Na⁺	1.3^d

^aBradbury and Baeyens, 2005.

^bBradbury and Baeyens, 2006.

^cGao et al., 2021.

^dKumar et al., 2013.

Table 8

Surface complexation constants on surface complexation sites (S^s-OH, S^w-OH, and S-OH) for selenium (Se) sorption on various bentonite samples.

Surface complexation / Cation exchange reaction	log K
FEBEX + 2SP-NE-SC
S^s-OH₂⁺ + SeO32− ↔ S^s-OH2SeO3−	12.0^a
S^w-OH₂⁺ + SeO32− ↔ S^w-OH2SeO3−	11.95^a
S^s-OH₂⁺ + HSeO₃⁻ ↔ S^s-OH2SeO3	17.9^a
S^w-OH₂⁺ + HSeO₃⁻ ↔ S^w-OH2SeO3	17.65^a
GMZ +2SP-DL-SC/CE
S-OH₂⁺ + HSeO₃⁻ ↔ S-SeO3+ H₂O	3.3^b
2S-OH + HSeO₃⁻ ↔ (S)2-SeO3 + H₂O + OH−	15.8^b
2S-OH + Eu³⁺ + HSeO₃⁻ ↔ (SO)2-EuSeO₃⁻ + 3H⁺	−1.1^b

^aMissana et al., 2009.

^bShi et al., 2014.

Table 9

Surface complexation constants and selectivity coefficients on surface complexation sites (S^s-OH, S^w-OH, S-OH) and cation exchange sites (X) for europium (Eu) sorption on various bentonite samples.

Surface complexation / Cation exchange reaction	log K
SWy-1 + 2SP-NE-SC/CE
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	1.6^a, b, 2.3^c
S^s-OH + Eu³⁺ + H₂O ↔ S^s-OEuOH⁺ + 2H⁺	−6.4^a, −5.9^{b, c}
S^s-OH + Eu³⁺ + 2H₂O ↔ S^s-OEu(OH)2 + 3H⁺	−15.7^a, −14.2^b, −13.9^c
S^s-OH + Eu³⁺ + 3H₂O ↔ S^s-OEu(OH)3− + 4H⁺	−25.8^c
S^s-OH + Eu³⁺ + CO₃²⁻ ↔ S^s-OEuCO₃ + H⁺	8.3^b
S^s-OH + Eu³⁺ + CO₃²⁻ + H₂O ↔ S^s-OEuOHCO₃⁻ + 2H⁺	−0.25^b
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	1.47^a, 1.46^b, 1.5^c
MX-80 + 2SP-NE-SC/CE
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	1.6^d
S^s-OH + Eu³⁺ + H₂O ↔ S^s-OEuOH⁺ + 2H⁺	−16.4^d
S^s-OH + Eu³⁺ + 2H₂O ↔ S^s-OEu(OH)2 + 3H⁺	−15.7^d
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	1.5^d
Jinchuan + 2SP-DL-SC/CE
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	1.3^{e, f}
S^w-OH + Eu³⁺ ↔ S^w-OEu²⁺ + H⁺	−2.0^{e, f}
S^w-OH + Eu³⁺ + H₂O↔ S^w-OEuOH⁺ + 2H⁺	−6.8^{e, f}
S^w-OH + Eu³⁺ + 3H₂O ↔ S^w-OEu(OH)3− + 4H⁺	−20.6^{e, f}
S^w-OH + Eu³⁺ + CO₃²⁻ ↔ S^w-OEuCO₃+ H⁺	8.2^e
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	1.3^{e, f}
GMZ + 2SP-DL-SC/CE
S-OH + Eu³⁺ + H₂O ↔ S^s-OEuOH⁺ + 2H⁺	−7.7^g
2S-OH + Eu³⁺ + HSeO₃⁻ ↔ (SO)2-EuSeO₃⁻ + 3H⁺	−1.1^g
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	2.0^g
Western India + 2SP-NE-SC/CE
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	1.87^h
S^s-OH + Eu³⁺ + H₂O ↔ S^s-OEuOH⁺ + 2H⁺	−5.4^h
S^s-OH + Eu³⁺ + 2H₂O ↔ S^s-OEu(OH)2 + 3H⁺	−20.2^h
S^w-OH + Eu³⁺ ↔ S^w-OEu²⁺ + H⁺	−0.3^h
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	1.3^h

^aBradbury and Baeyens, 2005.

^bFernandes et al., 2008.

^cSchnurr et al., 2015.

^dBradbury and Baeyens, 2011.

^eGuo et al., 2009.

^fChen et al., 2014.

^gShi et al., 2015.

^hKumar et al., 2013.

Table 10

Surface complexation constants and selectivity coefficients on surface complexation site (Al-OH) and cation exchange site (X) for europium (Eu) sorption on Jinchuan bentonite at elevated temperature condition (Tertre et al., 2006).

Surface complexation / Cation exchange reaction	log K
MX-80 + 2SP-DL-SC/CE
Al-OH + Eu³⁺ ↔ Al-OEu²⁺ + H⁺	−1.0^a, 2.5^b, 6.5^c, 7.5^d
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	5.4^{a, b, c, d}

^aT = 25℃.

^bT = 40℃.

^cT = 80℃.

^dT = 150℃.

Table 11

Surface complexation constants and selectivity coefficients on surface complexation site (S^s-OH, S^w1-OH) and cation exchange site (X) for europium (Eu) sorption on Na- and Ca-bentonite (Bradbury and Baeyens, 2002).

Surface complexation / Cation exchange reaction	log K
SWy-1 + 2SP-NE-SC/CE
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	1.8^a, 0.8^b
S^s-OH + Eu³⁺ + H₂O ↔ S^s-OEuOH⁺ + 2H⁺	−5.4^a, −5.7^b
S^s-OH + Eu³⁺ + 3H₂O ↔ S^s-OEu(OH)3− + 4H⁺	−22.1^a, −22.6^b
S^w1-OH + Eu³⁺ ↔ S^w1-OEu²⁺ + H⁺	−0.5^a, −1.2^b
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	1.8^a, 0.8^b
3Na-X + Eu³⁺ ↔ Eu-X₃ + 3Na⁺	1.47^{a, b}
3Ca-X₂ + 2Eu³⁺ ↔ 2Eu-X₃ + 3Ca2+	1.11^{a, b}

^aNa-montmorillonite.

^bCa-montmorillonite.

Table 12

Surface complexation constants on surface complexation sites (S^s-OH, S^w1-OH) for europium (Eu) sorption on FEBEX bentonite sample using different thermodynamic databases, EQ(3)/6 and ThermoChimie (Missana et al., 2021).

Surface complexation / Cation exchange reaction	log K
FEBEX+ 2SP-NE-SC/CE
S^s-OH + Eu³⁺ ↔ S^s-OEu²⁺ + H⁺	0.9^a, 1.24^b
S^s-OH + Eu³⁺ + 2H₂O ↔ S^s-OEu(OH)2 + 3H⁺	−12.2^a, −16.02^b
S^w1-OH + Eu³⁺ ↔ S^w1-OEu²⁺ + H⁺	−0.05^a, −0.32^b
S^w1-OH + Eu³⁺ + 2H₂O ↔ S^w1-OEu(OH)2 + 3H⁺	−13.62^a, −17.16^b
S^s-OH + Eu³⁺ + CO₃²⁻ ↔ S^s-OEuCO₃+ H⁺	−2.48^a, 7.68^b
S^w1-OH + Eu³⁺ + CO₃²⁻ ↔ S^w1-OEuCO₃+ H⁺	−3.36^a, 5.7^b

^aEQ(3)/6 (Delany and Lundeen, 1991).

^bThermoChimie (Guillaumont and Mompean, 2003).

Feb 28, 2025 Vol.58 No.1, pp. 1~97

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