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Characterization of silver-kaolinite (AgK): an adsorbent for long-lived (129)I species.

Sadasivam S, Rao SM - Springerplus (2016)

Bottom Line: Bentonite is a preferred buffer and backfill material for deep geological disposal of high-level nuclear waste (HLW).Bentonite does not retain anions by virtue of its negatively charged basal surface.The AgK is prepared by heating kaolinite-silver nitrate mix at 400 °C to study the kaolinite influence on the transition metal ion when reacting at its dehydroxylation temperature.

View Article: PubMed Central - PubMed

Affiliation: Geoenvironmental Research Centre, Cardiff University, Cardiff, CF24 3AA UK.

ABSTRACT
Bentonite is a preferred buffer and backfill material for deep geological disposal of high-level nuclear waste (HLW). Bentonite does not retain anions by virtue of its negatively charged basal surface. Imparting anion retention ability to bentonite is important to enable the expansive clay to retain long-lived (129)I (iodine-129; half-life = 16 million years) species that may escape from the HLW geological repository. Silver-kaolinite (AgK) material is prepared as an additive to improve the iodide retention capacity of bentonite. The AgK is prepared by heating kaolinite-silver nitrate mix at 400 °C to study the kaolinite influence on the transition metal ion when reacting at its dehydroxylation temperature. Thermo gravimetric-Evolved Gas Detection analysis, X-ray diffraction analysis, X-ray photo electron spectroscopy and electron probe micro analysis indicated that silver occurs as AgO/Ag2O surface coating on thermally reacting kaolinite with silver nitrate at 400 °C.

No MeSH data available.


a XRD patterns of AgK, Kaolinite, AgNO3 heated at 400 °C and silver (Ag); b X-ray patterns of 80 % kaolinite–20 % silver nitrate without heating and kaolinite
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Fig6: a XRD patterns of AgK, Kaolinite, AgNO3 heated at 400 °C and silver (Ag); b X-ray patterns of 80 % kaolinite–20 % silver nitrate without heating and kaolinite

Mentions: XRD patterns of AgK and kaolinite specimens are compared in Fig. 5a, b. The figure shows that the kaolinite mineral in AgK specimen retains its crystalline structure (Fig. 5) as depicted by the strong reflections at 7.1, 3.57 and 2.34 Å (2θ values of 12.45°, 24.91° and 38.4° respectively); comparatively silver nitrate reflections at 2θ values of 19.5°, 24.2°, 29.6° and 32.7° are absent in the XRD pattern of the AgK specimens. The XRD patterns of AgK specimen, silver nitrate heated at 400 °C and silver metal are also compared in Fig. 6a to identify the crystalline form of silver present in AgK specimen. The strong X-ray reflections of silver metal at 2θ values 38° and 44° are absent in the XRD pattern of AgK specimen. The X-ray reflections attribute to silver-nitrate were clearly present in the 20 % AgNO3–80 % kaolinite physical mix without heating (Fig. 6a). Further, though silver nitrate heated at 400 °C exhibits reflections at 2θ values 29.6°, 19.5° and 21.67° characteristic of AgNO3, these reflections are absent in the XRD pattern of AgK specimen. Similarlly, the XRD patterens of 20 %AgO–80 %kaolinite and 20 %Ag2O–80 %kaolinite were exhibits the representative peaks of the silver oxides (Fig. 7a). The absence of crystalline form of silver reflections in the XRD patterns indicating that the silver present in AgK specimen does not occur as Ag metal (or) AgNO3 molecule (or) kaolinite influences the X-ray reflections of certain forms of silver compounds (or) the silver oxides retained as amorphous coating on kaolinite surface. The 1 g of AgK specimen equilibrated with 100 mL of 1000 mg/L of chloride and iodide ions exhibited the X-ray reflection peaks attributed to the respective silver halides (Fig. 7b). This behaviour shows that the silver could be retained on kaolinite surface as oxide coating and interacts with halide ions as follow (Cotton et al.1995).3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$AgNO_{3} + H_{2} O \to AgOH + OH^{ - }$$\end{document}AgNO3+H2O→AgOH+OH-4\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$AgOH + I^{ - } \to AgI + OH^{ - }$$\end{document}AgOH+I-→AgI+OH-Fig. 5


Characterization of silver-kaolinite (AgK): an adsorbent for long-lived (129)I species.

Sadasivam S, Rao SM - Springerplus (2016)

a XRD patterns of AgK, Kaolinite, AgNO3 heated at 400 °C and silver (Ag); b X-ray patterns of 80 % kaolinite–20 % silver nitrate without heating and kaolinite
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Related In: Results  -  Collection

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Fig6: a XRD patterns of AgK, Kaolinite, AgNO3 heated at 400 °C and silver (Ag); b X-ray patterns of 80 % kaolinite–20 % silver nitrate without heating and kaolinite
Mentions: XRD patterns of AgK and kaolinite specimens are compared in Fig. 5a, b. The figure shows that the kaolinite mineral in AgK specimen retains its crystalline structure (Fig. 5) as depicted by the strong reflections at 7.1, 3.57 and 2.34 Å (2θ values of 12.45°, 24.91° and 38.4° respectively); comparatively silver nitrate reflections at 2θ values of 19.5°, 24.2°, 29.6° and 32.7° are absent in the XRD pattern of the AgK specimens. The XRD patterns of AgK specimen, silver nitrate heated at 400 °C and silver metal are also compared in Fig. 6a to identify the crystalline form of silver present in AgK specimen. The strong X-ray reflections of silver metal at 2θ values 38° and 44° are absent in the XRD pattern of AgK specimen. The X-ray reflections attribute to silver-nitrate were clearly present in the 20 % AgNO3–80 % kaolinite physical mix without heating (Fig. 6a). Further, though silver nitrate heated at 400 °C exhibits reflections at 2θ values 29.6°, 19.5° and 21.67° characteristic of AgNO3, these reflections are absent in the XRD pattern of AgK specimen. Similarlly, the XRD patterens of 20 %AgO–80 %kaolinite and 20 %Ag2O–80 %kaolinite were exhibits the representative peaks of the silver oxides (Fig. 7a). The absence of crystalline form of silver reflections in the XRD patterns indicating that the silver present in AgK specimen does not occur as Ag metal (or) AgNO3 molecule (or) kaolinite influences the X-ray reflections of certain forms of silver compounds (or) the silver oxides retained as amorphous coating on kaolinite surface. The 1 g of AgK specimen equilibrated with 100 mL of 1000 mg/L of chloride and iodide ions exhibited the X-ray reflection peaks attributed to the respective silver halides (Fig. 7b). This behaviour shows that the silver could be retained on kaolinite surface as oxide coating and interacts with halide ions as follow (Cotton et al.1995).3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$AgNO_{3} + H_{2} O \to AgOH + OH^{ - }$$\end{document}AgNO3+H2O→AgOH+OH-4\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$AgOH + I^{ - } \to AgI + OH^{ - }$$\end{document}AgOH+I-→AgI+OH-Fig. 5

Bottom Line: Bentonite is a preferred buffer and backfill material for deep geological disposal of high-level nuclear waste (HLW).Bentonite does not retain anions by virtue of its negatively charged basal surface.The AgK is prepared by heating kaolinite-silver nitrate mix at 400 °C to study the kaolinite influence on the transition metal ion when reacting at its dehydroxylation temperature.

View Article: PubMed Central - PubMed

Affiliation: Geoenvironmental Research Centre, Cardiff University, Cardiff, CF24 3AA UK.

ABSTRACT
Bentonite is a preferred buffer and backfill material for deep geological disposal of high-level nuclear waste (HLW). Bentonite does not retain anions by virtue of its negatively charged basal surface. Imparting anion retention ability to bentonite is important to enable the expansive clay to retain long-lived (129)I (iodine-129; half-life = 16 million years) species that may escape from the HLW geological repository. Silver-kaolinite (AgK) material is prepared as an additive to improve the iodide retention capacity of bentonite. The AgK is prepared by heating kaolinite-silver nitrate mix at 400 °C to study the kaolinite influence on the transition metal ion when reacting at its dehydroxylation temperature. Thermo gravimetric-Evolved Gas Detection analysis, X-ray diffraction analysis, X-ray photo electron spectroscopy and electron probe micro analysis indicated that silver occurs as AgO/Ag2O surface coating on thermally reacting kaolinite with silver nitrate at 400 °C.

No MeSH data available.