Advanced smectite alteration and the role of accessory reactants at 180 °C: New experimental constraints on the stability of bentonite

IF 5.3 2区 地球科学 Q2 CHEMISTRY, PHYSICAL
Ritwick Sudheer Kumar, Laurence N. Warr, Georg H. Grathoff, Balu R. Thombare
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引用次数: 0

Abstract

Bentonite clay is commonly accepted as an appropriate material for backfilling the space between the radioactive canisters and the host rock of planned underground repository sites for waste disposal. Despite its favourable properties as a hydrodynamic seal, its long-term stability remains a concern. This experimental study of a Bavarian bentonite investigated advanced montmorillonite (smectite) illitisation at 180 °C in the presence of K-oxalate and/or the accessory minerals of pyrite and calcite. The formation of mixed-layered illite-smectite was quantified by X-ray diffraction Rietveld refinement and the crystal chemistry was determined by transmission electron microscopy. The results showed neocrystallisation of a celadonitic illite-smectite (up to 63% illite-layers) after treatment with KCl or K-oxalate with increased Al3+ in the tetrahedral sheets, reduced amounts in the octahedral locations and increased fixation of non-exchangeable K+ ions in response to the increased layer charges. K-oxalate complexation of Al3+ and enhanced dissolution of the smectite resulted in the formation of a possible intermediate amorphous phase and illite-smectite crystallites with additional vacant sites explaining the lower number of octahedral ions (<2 per formula unit). Adding 10% pyrite, 10% calcite, or 5% of each, did influence the degree of alteration to a recognisable degree in the presence of KCl, but the effects on the rate of illitisation were minimal when reacted with K-oxalate, which further increased illitisation by up to 6.4 times. Although batch reactor experiments do have limitations compared to complex repository conditions, our results do indicate that claystone host rocks low in organic matter should be favoured over organic-rich lithologies that are likely to contain oxalate ligands or similar catalysing compounds.

180 °C下的高级钠长石蚀变和辅助反应物的作用:膨润土稳定性的新实验约束
人们普遍认为膨润土是一种合适的材料,可用于回填计划中的地下废物处置库的放射性罐与主岩之间的空间。尽管膨润土具有良好的流体动力密封特性,但其长期稳定性仍然令人担忧。这项对巴伐利亚膨润土的实验研究调查了在 K-草酸盐和/或黄铁矿和方解石等附属矿物存在的情况下,蒙脱石(smectite)在 180 ° C 的高温下发生先进的幻化。通过 X 射线衍射里特维尔德细化法对伊利石-直闪石混合层的形成进行了量化,并通过透射电子显微镜确定了晶体化学性质。结果表明,经 KCl 或 K-oxalate 处理后,青绿柱状伊利石-闪长岩(伊利石层高达 63%)发生了新结晶,四面体片中的 Al3+ 增加,八面体位置的 Al3+ 数量减少,不可交换的 K+ 离子的固定增加,以应对层电荷的增加。K-oxalate 对 Al3+ 的络合作用以及埃安石溶解度的提高导致形成了可能的中间无定形相和埃安石-埃安石结晶体,这些结晶体具有更多的空位,因此八面体离子的数量较少(每个公式单位为 2 个)。在氯化钾存在的情况下,添加 10%的黄铁矿、10%的方解石或各添加 5%的黄铁矿、方解石或各添加 5%的方解石,确实会在一定程度上影响蚀变程度,但在与草酸钾反应时,对辉变率的影响微乎其微,而草酸钾会进一步提高辉变率,最高可达 6.4 倍。虽然批量反应器实验与复杂的贮存条件相比有其局限性,但我们的结果确实表明,有机质含量低的粘土岩主岩应优先于有机质含量丰富的岩性,因为后者可能含有草酸盐配体或类似的催化化合物。
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来源期刊
Applied Clay Science
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...
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