Effect of thermal aging at 165 °C–200 °C on bentonite performance

IF 5.8 2区地球科学 Q2 CHEMISTRY, PHYSICAL

Applied Clay Science Pub Date : 2025-09-17 DOI:10.1016/j.clay.2025.107994

Sirpa Kumpulainen , Jari Martikainen , Teemu Laurila , Florian Kober , Olivier Leupin

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引用次数: 0

Abstract

The engineered barrier system in the deep geological repository will encounter varying design loads (hydraulic, mechanical, thermal and chemical) over time. The bentonite buffer may remain dry for long periods of time locally, where access to water from the host rock is low, and consequently, heat may build up increasing the buffer temperature leading to dehydration of smectite. The temperature for complete removal of interlayer water on the smectite is within >150 °C and depends on among others exchangeable cation, smectite type and confining pressure. Although dehydration reactions can be considered reversible, complete dehydration may lead to irreversible alterations. The objective of this work was to determine the effect of thermal aging on bentonite buffer performance.

Bentonite from Wyoming was thermally aged at 165 °C, 180 °C or 200 °C for 4 weeks, 8 weeks or 20 weeks in a dry, unsaturated state. Thereafter, bentonite was cooled down to room temperature and its properties and performance were evaluated determining the mineralogy by X-ray diffraction (XRD), cation exchange capacity (CEC), swelling index, and performing swelling pressure and hydraulic conductivity tests. Swiss repository conditions were applied for this work using granular bentonite mixture (GBM) and a target dry density of 1450 kg/m³ and Opalinus Clay synthetic porewater (TDS of 16.92 g/l) in swelling pressure and hydraulic conductivity experiments.

Mineralogical changes observed include dehydration of gypsum and change in clay suspension color indicating small changes in iron oxide mineral phases or contents. No impact on the swelling pressure was noted due to thermal aging, but thermally aged samples had a factor of 1.8 higher hydraulic conductivity compared to references. In addition, up to 4 % decrease in apparent CEC, and up to 25 % decrease in swelling index and faster settling of clay suspensions were observed to occur with thermal aging time and temperature. One potential explanation for observed changes is partial fixation of exchangeable cations and consequent changes in particle size due to heat exposure.

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165℃- 200℃热老化对膨润土性能的影响

随着时间的推移，深层地质储存库中的工程屏障系统将遇到不同的设计载荷（水力、机械、热和化学）。膨润土缓冲层可能在局部保持干燥很长一段时间，因为从宿主岩石中获得的水分很少，因此，热量可能会积聚，增加缓冲层的温度，导致蒙脱石脱水。完全去除蒙脱石层间水的温度在150℃以内，这取决于交换阳离子、蒙脱石类型和围压等因素。虽然脱水反应可以被认为是可逆的，但完全脱水可能导致不可逆的改变。本工作的目的是确定热老化对膨润土缓冲性能的影响。怀俄明州的膨润土在165°C， 180°C或200°C下在干燥，不饱和状态下热老化4周，8周或20周。随后，将膨润土冷却至室温，通过x射线衍射（XRD）、阳离子交换容量（CEC）、溶胀指数、溶胀压力和水导率测试等方法对膨润土的矿物学特征进行评价。本研究采用瑞士储库条件，采用颗粒状膨润土混合物（GBM），目标干密度为1450 kg/m3， Opalinus Clay合成孔隙水（TDS为16.92 g/l）进行膨胀压力和水力导率实验。观察到的矿物学变化包括石膏脱水和粘土悬浮液颜色的变化，表明氧化铁矿物相或含量的微小变化。热老化对膨胀压力没有影响，但热老化样品的水力导率比参考样品高1.8倍。此外，随着热老化时间和温度的增加，表观CEC降低了4%，膨胀指数降低了25%，粘土悬浮物的沉降速度加快。对观察到的变化的一个可能的解释是，由于热暴露，可交换阳离子的部分固定和随之而来的颗粒大小变化。

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来源期刊

Applied Clay Science 地学-矿物学

CiteScore

10.30

自引率

10.70%

发文量

289

审稿时长

39 days

期刊介绍： Applied Clay Science aims to be an international journal attracting high quality scientific papers on clays and clay minerals, including research papers, reviews, and technical notes. The journal covers typical subjects of Fundamental and Applied Clay Science such as: • Synthesis and purification • Structural, crystallographic and mineralogical properties of clays and clay minerals • Thermal properties of clays and clay minerals • Physico-chemical properties including i) surface and interface properties; ii) thermodynamic properties; iii) mechanical properties • Interaction with water, with polar and apolar molecules • Colloidal properties and rheology • Adsorption, Intercalation, Ionic exchange • Genesis and deposits of clay minerals • Geology and geochemistry of clays • Modification of clays and clay minerals properties by thermal and physical treatments • Modification by chemical treatments with organic and inorganic molecules(organoclays, pillared clays) • Modification by biological microorganisms. etc...