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The importance of the dehydroxylation temperature of swellable clay minerals for their environmental geotechnical properties

Abstract:


Bentonites play an important role in the Environmental Geotechnics all over the world. Swellable smectites are used as liners and adsorber in waste deposits, for hazardous waste remediation or for isolating radioactive waste. The bentonites in these deposits are exposed to lecheate and water steam at temperatures between 50 C and 120 C caused by reactions in the waste deposit. These conditions lead to changed material properties and a loss of quality.

Montmorillonite is the main component of bentonites and therefore responsible for the properties of the barrier material. We will show the relationship between the changes of the structure of dioctahedral smectites and their dehydroxylation behaviour, respectively, and the geotechnical macroscopic properties.

Montmorillonites, which adsorbed heavy metals from the lecheate, are subjected to the Hofmann-Klemen-effect at temperatures >90 C. E. g. Cu 2+-ions migrate from interlayer positions into octahedral vacancies and could cause a loss of swellability. Water steam at T > 100 C also causes a movement of Cu 2+ -ions into octahedral positions and Mg 2+ occurred exchangeable in interlayer positions. As the result of these movement of ions in the structure, the specific bonds of the hydroxyl groups have changed and a changed dehydroxylation behaviour could be expected, which is related to geotechnical properties.

Authors:

Amann, Peter and Kahr, Günter and Emmerich, Katja and Lagaly, Gerhard

Index Terms:

ClayGroup; dehydroxylation; rehydroxylation

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