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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.


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High resolution X-ray photo electron spectrum of silver (Ag) 3d and 4d (insert) of silver oxides obtained from AgK specimen
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Fig9: High resolution X-ray photo electron spectrum of silver (Ag) 3d and 4d (insert) of silver oxides obtained from AgK specimen

Mentions: Figures 8a, b depict the photon emission survey spectra of kaolinite and AgK specimens. The XPS peak doublets at binding energies of 368.1 eV (electron volts) and 374 eV result from silver’s d-subshell spin orbital splitting 3d5/2 and 3d3/2 respectively (Wagner et al. 1979). The high resolution spectrum of silver’s d-shell spin orbital splitting is presented in Fig. 9. The FWHM (Full Width Half Maximum) of 3d5/2 peak corresponds to 1.45 eV. Hoflund and Hazos (2000), Bielmann et al. (2002) Weaver and Hoflund (1994) reported that the FWHM values of 3d5/2 peaks of Ag, AgO and Ag2O correspond to 0.57 eV, 1.57 eV and 1.5 eV respectively. According to available studies (Weaver and Hoflund 1994; Hoflund and Hazos 2000; Bielmann et al. 2002; Chiu et al. 2003; Al-Kuhaili 2007; Gao et al. 2004), the relatively high FWHM of 3d5/2 peak (1.45 eV) in Fig. 8 suggests the existence of AgO and Ag2O in AgK specimen. As the photoemission spectra is a surface phenomenon (approximate penetration depth is 1–5 nm, Seyama et al. 2006; Vempati et al. 1996) the silver oxides in AgK specimen occur as surface coatings. The O1s peak identified at 537.2 eV and 539.15 eV in silver–kaolinite and kaolinite respectively. The 4d peak of silver at 4.9 eV attribute to native silver oxides (Fig. 9; Vincent 2005).Fig. 8


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

Sadasivam S, Rao SM - Springerplus (2016)

High resolution X-ray photo electron spectrum of silver (Ag) 3d and 4d (insert) of silver oxides obtained from AgK specimen
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4764597&req=5

Fig9: High resolution X-ray photo electron spectrum of silver (Ag) 3d and 4d (insert) of silver oxides obtained from AgK specimen
Mentions: Figures 8a, b depict the photon emission survey spectra of kaolinite and AgK specimens. The XPS peak doublets at binding energies of 368.1 eV (electron volts) and 374 eV result from silver’s d-subshell spin orbital splitting 3d5/2 and 3d3/2 respectively (Wagner et al. 1979). The high resolution spectrum of silver’s d-shell spin orbital splitting is presented in Fig. 9. The FWHM (Full Width Half Maximum) of 3d5/2 peak corresponds to 1.45 eV. Hoflund and Hazos (2000), Bielmann et al. (2002) Weaver and Hoflund (1994) reported that the FWHM values of 3d5/2 peaks of Ag, AgO and Ag2O correspond to 0.57 eV, 1.57 eV and 1.5 eV respectively. According to available studies (Weaver and Hoflund 1994; Hoflund and Hazos 2000; Bielmann et al. 2002; Chiu et al. 2003; Al-Kuhaili 2007; Gao et al. 2004), the relatively high FWHM of 3d5/2 peak (1.45 eV) in Fig. 8 suggests the existence of AgO and Ag2O in AgK specimen. As the photoemission spectra is a surface phenomenon (approximate penetration depth is 1–5 nm, Seyama et al. 2006; Vempati et al. 1996) the silver oxides in AgK specimen occur as surface coatings. The O1s peak identified at 537.2 eV and 539.15 eV in silver–kaolinite and kaolinite respectively. The 4d peak of silver at 4.9 eV attribute to native silver oxides (Fig. 9; Vincent 2005).Fig. 8

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.


Related in: MedlinePlus