Methodology for studying the composition of non-interlamellar pore water in compacted bentonite

Abstract

Many safety functions required of the compacted bentonite buffer in the KBS-3 concept rely on processes influenced by the composition of the pore water. Important safety-relevant processes are related to the bentonite buffer,e.g.swelling, precipitation and dissolution reactions, and transport of water, colloids and ions. One of the methods used in analysing pore water in compacted bentonite is the ‘squeezing technique’. Various possible artefacts which can occur during squeezing, such as mixing of different pore-water types, dissolution of accessory minerals and cation exchange, need special attention.The present work describes the methodology for studying the composition of the non-interlamellar pore water by combining squeezing methods, chemical analyses, microstructure measurements and geochemical modelling. Four different maximum pressures were used to squeeze the compacted bentonite pore water. The origin of the pore water was studied by analysing the bentonite microstructure both before and after squeezing using SAXS and NMR, the cation exchange and dissolution reactions were studied by chemical analyses and geochemical modelling.The pore-water yield increased from 32 to 48 wt.% from the initial amount of porewater in the samples when the maximum squeezing pressure was increased from 60 MPa to 120 MPa. About 35 wt.% of the water collected originated from the interlamellar (IL) pores. The ratio between IL and non-IL pore waters as well as the composition of the squeezed porewater was constant in the squeezing-pressure range used. The results of microstructural measurements by SAXS were in perfect agreement with previous studies (e.g.Muurinen & Carlsson, 2013). The dissolving accessory minerals have an effect on the ratio of the cations in the squeezed solution while the migration of anions in bentonite seems to be diffusion limited. According to geochemical modelling the chloride concentration of the non-IL pore water in compacted bentonite before squeezing was 0.34 Mgreater than in the squeezed pore water due to the mixing of two main water types.

Database for validation of thermo-hydro-chemo-mechanical behaviour in bentonites

“…Other clayey materials such as Opalinus Clay (Appelo and Wersin 2007;Mäder 2004) from Mont Terri (Switzerland), the Callovo-Oxfordian Clay (Gaucher et al 2004) from Meuse/Haute-Marne Underground Research Laboratory (URL) located at Bure (France) and the Boom Clay (Maes et al 2002;Romero et al 1999) of Mol (Belgium) are also being currently studied as potential parameterisation and then validated by comparing the results with those obtained in experimental tests. The experimental tests most extensively carried out for this purpose have been: free swelling tests (Chen and Huang 2013;Jönsson et al 2009;Li et al 2019;Shehata et al 2020), swelling pressure tests (Brachman et al 2021;Castellanos et al 2008;He et al 2019;Karnland 1997;Komine et al 2009;Pusch 2001;Sun et al 2015;Zhang et al 2019;Zhu et al 2013), swelling under load test (Castellanos et al 2006;Chen et al 2017;Di Maio et al 2004;Herbert et al 2008;Lee et al 2012;Shehata et al 2020;Studds et al 1996;Xiang et al 2019), and squeezing tests (Fernández and Villar 2010;Järvinen et al 2018), all of them conducted under different thermal and chemical conditions. The free swelling test aims to identify expansive clays and is generally based on measuring the change in volume of the material when it comes into contact with an aqueous phase.…”

Engineered Barrier System Research Activities at LBNL (FY2020 Progress Report)

“…For the remainder of FY20, we will complete this hydration testing, followed by a detailed dismantling of both heated and non-heated clays. The clays will be carefully removed and measured for water content, mineralogy changes, and chemistry of pore water, following techniques outlined by previous work on heated clays (Cuevas, 1997;Järvinen, 2016). Following the dismantling, we will repack the columns, focusing on the correspondence mineral density and the water chemistry to such characteristics determined the HotBENT field site.…”

Second ISSMGE R. Kerry Rowe Lecture: On the intrinsic, state, and fabric parameters of active clays for contaminant control

“…A possible explanation for this observation can be obtained by taking into account the physical significance of the NMR results, since there is a risk of underestimating the inter-tactoid porosity. In very high density samples, the difference between the average size of the inter-tactoid pores and the intra-tactoid pores is not sufficiently large to discern the two pore types with this method (Järvinen et al 2016). Thus, further study is recommended in order to improve the reliability of NMR for fine-grained soils, with a focus on evaluating to what extent the behaviour of D r a f t the water contained inside the conductive pores is affected by magnetic interactions with the solid phase.…”