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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.


TG and DSC pattern of AgK specimen
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Fig4: TG and DSC pattern of AgK specimen

Mentions: The thermo gravimetry (TG) and ion current pattern of 80 % kaolinite + 20 % silver nitrate mix however exhibits a two-step weight loss pattern (Fig. 3a). The first weight loss commences around 212 °C corresponding to melting point of silver nitrate (Fig. 3). The silver nitrate and kaolinite specimens did not show any weight loss around 212 °C (Figs. 1 and 2). In the temperature range of 212–400 °C, the ion current pattern of the kaolinite–silver nitrate mix (Fig. 3) exhibits the release of NO and NO2 gases from decomposition of silver nitrate and some release of water molecules from dehydroxylation of kaolinite. This behaviour was further investigated by heating the same composition of the materials at 400 °C for 30 min (Fig. 3b). The Fig. 3b clearly shows the water peak and the NO and NO2 gases release at 400 °C and also indicates the reaction rate was well within 30 min time period. In the temperature range of 450–600 °C the second step weight loss occurs (Fig. 3). In this temperature range, ion current pattern shows large release of water molecules from kaolinite. The TG plot also shows that 19.2 mg of 80 % kaolinite + 20 % silver nitrate mix lose 3.2 mg, corresponding to weight loss of 16.76 %. The weight loss observed during step one (8.9 %, Fig. 3) is comparable with the weight loss measurement (9.2 %, Table 2) observed on heating the 80 % kaolinite + 20 % silver nitrate in the furnace at 400 °C for 30 min. The thermo gravimetry (TG) and differential scanning calorimetry (DSC) patterns of AgK specimen in Fig. 4 do not show the endothermic peak at 212 °C (corresponding to melting point of silver nitrate) indicating the absence of free silver nitrate in the AgK specimen.Fig. 3


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

Sadasivam S, Rao SM - Springerplus (2016)

TG and DSC pattern of AgK specimen
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

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

Fig4: TG and DSC pattern of AgK specimen
Mentions: The thermo gravimetry (TG) and ion current pattern of 80 % kaolinite + 20 % silver nitrate mix however exhibits a two-step weight loss pattern (Fig. 3a). The first weight loss commences around 212 °C corresponding to melting point of silver nitrate (Fig. 3). The silver nitrate and kaolinite specimens did not show any weight loss around 212 °C (Figs. 1 and 2). In the temperature range of 212–400 °C, the ion current pattern of the kaolinite–silver nitrate mix (Fig. 3) exhibits the release of NO and NO2 gases from decomposition of silver nitrate and some release of water molecules from dehydroxylation of kaolinite. This behaviour was further investigated by heating the same composition of the materials at 400 °C for 30 min (Fig. 3b). The Fig. 3b clearly shows the water peak and the NO and NO2 gases release at 400 °C and also indicates the reaction rate was well within 30 min time period. In the temperature range of 450–600 °C the second step weight loss occurs (Fig. 3). In this temperature range, ion current pattern shows large release of water molecules from kaolinite. The TG plot also shows that 19.2 mg of 80 % kaolinite + 20 % silver nitrate mix lose 3.2 mg, corresponding to weight loss of 16.76 %. The weight loss observed during step one (8.9 %, Fig. 3) is comparable with the weight loss measurement (9.2 %, Table 2) observed on heating the 80 % kaolinite + 20 % silver nitrate in the furnace at 400 °C for 30 min. The thermo gravimetry (TG) and differential scanning calorimetry (DSC) patterns of AgK specimen in Fig. 4 do not show the endothermic peak at 212 °C (corresponding to melting point of silver nitrate) indicating the absence of free silver nitrate in the AgK specimen.Fig. 3

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.