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

Sivachidambaram Sadasivam,Sudhakar M Rao

doi:10.1186/s40064-016-1855-8

Sivachidambaram Sadasivam, Sudhakar M Rao

Open Access

https://doi.org/10.1186/s40064-016-1855-8

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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 129I (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.

Highlights

Bentonite is identified as potential buffer material in deep geological repositories for disposal of high level radioactive wastes (HLW) owing to its very low hydraulic conductivity, large swelling ability and high adsorptive capacity to retain cations (Pusch 2008)
Guided by the increased amounts of silver retention by kaolinite at elevated temperatures, the present study focuses on the kaolinite’s influence on the transition element and discuss the possible reaction mechanism of silver nitrate and kaolinite at 400 °C
The much larger weight loss experienced by the kaolinite–silver nitrate mix was attributed to salt-catalysed dehydroxylation phenomena (Kallai 1978)

Summary

Introduction

Bentonite is identified as potential buffer material in deep geological repositories for disposal of high level radioactive wastes (HLW) owing to its very low hydraulic conductivity, large swelling ability and high adsorptive capacity to retain cations (Pusch 2008). On heating at temperatures below 600 °C, kaolinite reacts with alkali metal salts (MX) according to the equation: It appears that on set of dehydroxylation (Temperature range from 400 to 550 °C; above dehydration but below dehydroxylation) the clay becomes reactive and concurrently, the liberated water dissolves adjacent salt particles and catalyses the reaction (Kallai 1978). This property of kaolinite could be exploited to incorporate silver compounds on the particle surface as they (example silver oxide) have strong affinity for formation of insoluble halides (Cotton et al 1995). In the present work, the silver treated kaolinite material has been prepared as an additive to bentonite to improve iodide retention capacity

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