Bentonite-rich clays have been chosen as the sealing material in the engineered barrier system of the deep geological repository (DGR) for the long-term storage of used nuclear fuels. Natural organic matter (NOM) found in these bentonites can serve as a source of nutrients for microbial growth. Although high density bentonite does not support microbial activity within its matrix, it is possible that microbial growth will occur at interface of the DGR rock wall and the bentonite; the availability of nutrients is therefore a design consideration. Furthermore, it is unclear if NOM is similar in composition within bentonite samples collected from different locations from the same naturally-occurring clay deposit, or whether NOM chemistry will vary within different batches.

Here, we report the detailed geochemical characterisation of different nutrients and NOM in five different MX-80 bentonites from the same location, but collected in different lots. Our results show that total carbon comprises <1% and that organic carbon constitutes less than one-fifth of this total carbon content. Statistical analyses revealed no significant differences in the NOM composition, or the other geochemical characteristics, of these samples. Targeted organic compound analyses indicated a predominance of long-chain homologues in the aliphatic lipids of the bentonites, suggesting that NOM in MX-80 bentonites is primarily terrestrially-derived. We detected nanogram-level variabilities in the concentrations of selected compounds between samples, but these variabilities were not statistically significant. Analysis by solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy also showed consistency between the NOM of the different MX-80 samples and a predominance of aliphatic, as well as aromatic compounds, which suggests that the NOM has undergone extensive diagenesis.

Overall, all analyses consistently indicated that the NOM composition exhibits low heterogeneity between the different bentonites mined from the same source. These results provide confidence in the potential use of MX-80 as a buffer material for widespread use in DGRs and they build upon past research on the NOM composition of bentonite clays.

富含膨润土的粘土已被选作深层地质处置库（DGR）的工程屏障系统中的密封材料，用于长期储存用过的核燃料。这些膨润土中发现的天然有机物（NOM）可以为微生物生长提供营养。尽管高密度膨润土在其基质中不支持微生物活性，但微生物生长可能会发生在DGR岩壁和膨润土的界面处。因此，营养物的可用性是设计考虑因素。此外，尚不清楚从同一天然粘土矿床的不同位置收集的膨润土样品中，NOM的成分是否相似，或者在不同批次中NOM的化学性质是否会有所不同。

在这里，我们报告了来自同一位置但收集在不同批次中的五种不同MX-80膨润土中不同养分和NOM的详细地球化学特征。我们的结果表明，总碳含量不到1％，有机碳含量不到总碳含量的五分之一。统计分析表明，这些样品的NOM组成或其他地球化学特征没有显着差异。有针对性的有机化合物分析表明，膨润土的脂族脂质中长链同系物占优势，这表明MX-80膨润土中的NOM主要来自陆地。我们检测到样品之间所选化合物浓度的纳克级差异，但这些差异在统计学上并不显着。固态分析¹³ C核磁共振（NMR）光谱还显示出不同MX-80样品的NOM与主要的脂肪族化合物以及芳香族化合物之间的一致性，这表明NOM已经历了广泛的成岩作用。

总体而言，所有分析均一致表明，从相同来源开采的不同膨润土之间，NOM成分的异质性较低。这些结果为将MX-80用作DGR中广泛使用的缓冲材料提供了信心，并且它们是基于对膨润土NOM组成的以往研究而建立的。