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In Sweden, a dry cover solution is commonly used to stop sulfide oxidation and the production of acid rock drainage from unattended sulfidic mine waste. Recycling a non-hazardous industrial residue, such as green liquor dregs (GLD) generated during pulp production, in this cover solution is beneficial for both the mining industry where there is a great need for cover materials and the pulp production industry. The objectives of this field study were to install and evaluate the instrumentation of sealing layers made of GLD- and bentonite-amended till, and to evaluate the practical aspects of two different methods of installation: monitoring wells and pits. This practical field study demonstrated that it is difficult to properly seal the drill holes after installing the probes in observation wells and suggests that a better (easier and less costly) alternative for future instrument installation in a sealing layer might be to excavate a pit in the protective layer after installation of the soil cover and then drill the probes into the sealing layer from that pit. [ABSTRACT FROM AUTHOR]

Highly diverse and well preserved organic-walled phytoplankton were recorded from the Darriwilian–early Katian interval of the Borenshult-1 drillcore. We identified 154 species in 53 genera, and three assemblages were distinguished; Assemblage A of a late Darriwilian age, Assemblage B of a Sandbian age (further subdivided into sub-assemblages B1 and B2), and Assemblage C dated as Katian. Taxa with "Silurian affinities" with previous first appearance datum in the early Silurian, Hirnantian, such as Metaleiofusa and Visbysphaera, are here recorded from the late Darriwilian and Sandbian respectively. These occurrences question the relationship between the appearance of pioneering phytoplankton morphotypes and the Hirnantian glaciation. Other taxa with no pre-Silurian records such as Visbysphaera pirifera subsp. minor, Petaloferidium cazurrum and Dorsennidium cf. D. estrellitae are here present in the Sandbian, where bentonite beds are intercalated. The diversity curve of acritarchs shows similarities with those proposed for the Darriwilian-Katian of Baltica with main differences in the interval with bentonite beds representing an intense volcanic activity. The species Metaleiofusa arcuata Wall is here emended and a new combination is proposed: Petaloferidium cazurrum (Cramer) comb. nov. The genus Fankea is recorded for the first time from Swedish strata, suggesting a dominant high- to middle latitudinal distribution instead of a Perigondwanan distribution. We contend that the location of paleo-southern Sweden contributed to the great diversity seen, since a middle-low latitude provided a suitable habitat with warm, shallow water, rich in nutrients. [ABSTRACT FROM AUTHOR]

At present, the deep geological repository concept for spent nuclear fuel is considered the most reliable and safe technique for the permanent disposal of this type of waste. One of the many safety elements used is an engineered barrier made of compacted bentonite. This material allows the encapsulated waste to be isolated from the host rock. Therefore, there is great interest in a detailed study of the behavior of bentonites to different changes in the composition of the surrounding groundwater. In this context, this work presents a new reactive transport model for bentonites implemented in the COMSOL Multiphysics platform. The model contemplates a non-simplistic geochemical system composed of 42 species and 4 minerals. Reactive transport involves the diffusive-dispersive-advective processes defined by the Nernst Planck equations for two overlapping modeling levels (macro- and microstructural) to simulate the behavior of double-porosity media. The uniqueness of this model is that the system of equations used to calculate the chemical speciation problem and the advective-diffusive-dispersive transport can be integrally solved in COMSOL. The model has been satisfactorily verified and validated using the benchmark exercise consisting of the simulation of the multicomponent advective-diffusive column experiment conducted on a compacted bentonite core extracted from a field experiment (LOT project) in the Äspö Hardrock laboratory (Sweden)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Graphical abstract Highlights • A cost-efficient and stable BZ for HMs removal from SW have been synthesized. • Gasification of rice husk effectively improves specific surface area and pore size. • The q m values of BZ for Cu2+ and Zn2+ are 16.39 and 12.72 mg·g−1, respectively. • NH 4 +-N over 500 mg·L−1 has significant effect on the adsorption capacity of BZ. • The BZ shows higher removal efficiency of HMs than AZ and bentonite in real SW. Abstract The preparation of bentonite–zeolite (BZ) adsorbent using bentonite, aluminate, and rice husk was conducted. The adsorption experiment was performed for the removal of Cu2+ and Zn2+ from aqueous solution in single and binary systems. Results showed that gasification of rice husk could effectively improve the specific surface area and pore volume. The optimum pH for Cu2+ and Zn2+ adsorption on BZ was pH 5.0. The pseudo-first order kinetic and Langmuir isotherm model of BZ were the optimal model for Cu2+ and Zn2+. According to Langmuir isotherm model, the maximum adsorption capacity value (q m) was 16.39 and 12.72 mg·g−1 for Cu2+ and Zn2+, respectively. The adsorption affinity order of BZ in the binary solution was Cu2+ > Zn2+. NH 4 +-N concentration over 500 mg·L−1 significantly affected the adsorption capacity of BZ (P < 0.05). The adsorption capacity of BZ for Cu2+ and Zn2+ was higher than that artificial zeolite (AZ) and bentonite in SW. [ABSTRACT FROM AUTHOR]

High-density sodium bentonite combines a low permeability with a swelling behavior, which constitute two important qualities for engineered barriers in geological disposal of spent nuclear fuel. For example, the KBS-3V method developed in Sweden and Finland is planned to include compacted bentonite as the buffer material to embed canisters containing the spent nuclear fuel packages in deposition holes in deep crystalline bedrock. The partially saturated bentonite buffer will then swell as it takes up groundwater from the surrounding rock. It is important to quantify the water content evolution of the installed buffer to correctly predict the development of the swelling pressure and the prevailing conditions (thermal, mechanical, chemical and biological). This study aimed at quantifying the water content profile at the surface of a cylindrical bentonite parcel retrieved after in situ wetting in fractured crystalline bedrock. We demonstrate the possibility of using regression-kriging to quantitatively include spatial information from high-resolution photographs of the retrieved bentonite parcel, where more water saturated areas appear as relatively dark shades, along with bentonite samples, where detailed measurements of water content were performed. The resulting reconstruction is both exact regarding local sample measurements and successful to reproduce features such as intersecting rock fracture traces, visible in the photographs. This level of detail is a key step to gain a deeper understanding of the hydraulic behavior of compacted bentonite barriers in sparsely fractured rock. An improved scanning procedure could further increase the accuracy by reducing errors introduced by the geometrical transformations needed to unfold and stitch the different photographs into a single gray scale map of the bentonite surface. The application of this technique could provide more insights to ongoing and planned experiments with unsaturated bentonite buffers. [ABSTRACT FROM AUTHOR]

The Borenshult-1 core, drilled in the vicinity of Motala, east of Lake Vättern in south central Sweden, comprises a well-dated and nearly complete succession of marine marly carbonates deposited relatively close to land. The 34 core samples analyzed for palynology encompass the upper part of the Darriwilian (Furudal Limestone), the entire Sandbian (Dalby Limestone, the Kinnekulle K-bentonite and the lower Skagen Limestone) and the lower part of the Katian (Skagen Limestone). The age of this interval is well-constrained to the late Darriwilian (Stage slice Dw3)–early Katian (Stage slice Ka1), based on conodonts and 206Pb/238U dating of volcanic ash deposits. The samples yielded predominantly marine organic-walled phytoplankton, mainly acritarchs, with subordinate chitinozoans, scolecodonts and fragments of graptolites. Sparse terrestrial palynomorphs, represented by cryptospores and trilete spores, were also found in 23 of the samples. A total of 154 acritarch species corresponding to 53 genera were identified, as well as low percentages of abnormal forms (teratological forms) of acritarch species at some levels. The strati­graphic distribution of genera and species allowed for three palynological assemblages to be distinguished: Assemblage A of a late Darriwilian age, Assemblage B of a Sandbian age (further subdivided into sub-assemblages B1 and B2), and Assemblage C dated as Katian. Genera such as Baltisphaeridium, Ordovicidium, Pachysphaeridium and Orthosphaeridum, which are common in Middle Ordovician phytoplankton assemblages from Baltica, are well represented, with several species, mainly in Assemblage A and sub-assemblage B1, up to the lower Sandbian. However, the presence of a majority of taxa with worldwide distribution supports the cosmopolitanism of the studied assemblages, already proposed to begin near the Darriwilian–Sandbian transition. Notably, phytoplankton taxa with Silurian affinities, previously known from the Hirnantian, appear for the first time in the late Darriwilian part of the Borenshult-1 drillcore (Dw3). Important taxa occurring are Tylotopalla and Metaleiofusa, which is definitively established from the beginning of the Sandbian (early Late Ordovician), together with the first appearance of the genus Visbysphaera. These occurrences question the relationship between the appearance of pioneering phytoplankton morphotypes and the Hirnantian glaciation. Other taxa with no pre-Silurian records such as Visbysphaera pirifera subsp. minor, Petaloferidium cazurrum and Dorsennidium cf. D. estrellitae are here present in the Sandbian, where bentonite beds are intercalated. The genus Frankea is recorded for the first time from the Ordovician of Sweden, suggesting a high to middle latitudinal distribution instead of a peri-Gondwanan distribution. The highest diversity corresponds to the Darriwilian and partly to the Sandbian assemblages, followed by a significant decline in the Katian. The main changes are observed in the Sandbian, with a significant drop in diversity, which is probably related to intense volcanic activity rep­resented by the bentonite beds. Diversity as well as origination and turnover rates are the lowest in the interval bearing the suite of K-bentonites, particularly near the thickest of them. The marked drop in diversity in the Katian part of the succession, visible in both low originations and abundance, is possibly related to a regression at the onset of the GICE (Guttenberg isotope carbon excursion), with less favorable environmental and climatic conditions. Changes in phytoplankton assemblages together with the onset of innovative morphologies of acritarchs were previously interpreted as a consequence of environmental and climatic perturbations related to the Ordovician glaciation. Here we show that the first appearances of these advanced taxa already occurred ca 15 Ma earlier, suggesting that a possible combination of factors such as sea level changes and volcanism triggered these changes, instead of a major event such as the Hirnantian glaciation. Additionally, these new findings challenge previous models of evolution and radiation of the Ordovician phytoplankton and set up Baltica as a new key area for paleogeographical research. [ABSTRACT FROM AUTHOR]

This paper reports on the geochemistry of the mid-Silurian Grötlingbo Bentonite, a ca. 0.1–0.4-m-thick and regionally important bentonite bed in Sweden and the East Baltic area. A series of eight samples, spaced by 5 cm, were taken from the Hunninge-1 drillcore in Gotland, Sweden, and were analysed in order to establish the vertical element composition and variation in the bentonite. The results show that the Götlingbo Bentonite originates from one source magma and from one single eruption. The lowermost 0.1–0.15 m of the bentonite (compacted) was deposited from air-transport fall-out, whereas the upper portions have been reworked in a shallow-marine environment and re-deposited. Vertical differences in Ti and Zr within the Grötlingbo Bentonite mean that regional correlation of the bed may need several samples at each locality to be reliable. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the initial results from a large scale gas injection test (Lasgit) performed at the Äspö Hard Rock Laboratory, Sweden. Lasgit is a full-scale field-scale experiment based on the Swedish KBS-3V repository concept, examining the processes controlling gas and water flow in compact buffer bentonite. The first 2 years of the test focused on the artificial hydration of the bentonite buffer. This was followed by a programme of hydraulic and gas injection tests which ran from day 843 to 1110. A further period of artificial hydration occurred from day 1110 to 1385, followed by a more complex programme of gas injection testing which remains on going (day 1385+). After 2 years of hydration, hydraulic conductivity and specific storage values in the lower filter array were found to range from 9×10−14 to 1.6×10−13 m/s and 5.5×10−5 to 4.4×10−4 m−1 respectively, with the injection filter FL903 yielding values of 7.5×10−14 m/s and 2.5×10−5 m−1. A second set of hydraulic measurements were performed over 1 year and a half later yielding similar values, in the range 7.8×10−14 m/s and 1.3×10-13 m/s. The hydraulic conductivity of FL903 had reduced slightly to 5.3×10−14 m/s while specific storage had increased to 4.0×10−5 m−1. Both datasets agree with laboratory values performed on small-scale saturated samples. Two sets of gas injection tests were performed over a 3 year period. During the course of testing, gas entry pressure was found to increase from around 650kPa to approximately 1.3MPa, indicative of the maturation of the clay. The sequential reduction in volumetric flow rate and lack of correlation between the rate of gas inflow and the gas pressure gradient observed during constant pressure steps prior to major gas entry, is suggestive of a reduction in gas permeability of the buffer and indicates only limited quantities of gas can be injected into the clay without interacting with the continuum stress field. Major gas entry occurs at a gas pressure close to, or slightly in excess of, the local stress state and is associated with a rapid increase in flux, linked to a series of kicks in axial and radial stress and porewater pressure. Post peak gas flux exhibits dynamic behaviour, symptomatic of unstable gas flow. When gas injection is stopped, flux into the clay rapidly reduces before entering an extended period of very small flows. This is accompanied by a rapid reduction in pressure which decays to an asymptotic value close to that of the total stress locally within the deposition hole. Examination of the data shows considerable evidence for the development of a highly-dynamic, tortuous network of pressure induced pathways which evolve both temporally and geospatially within the clay, opening and closing due to local changes in gas pressure and/or effective stress. These detailed observations do not conform to standard concepts of two-phase flow. The bentonite response to the passage of gas suggests that pathway dilation is the primary mechanism governing gas migration within the Lasgit system. The important coupling between gas, stress and porewater pressure at the repository scale is clearly evident with the data. The importance and interdependencies of this coupling will be investigated in future experiments planned at the Lasgit experimental site. [Copyright &y& Elsevier]

Abstract: Silica sol, i.e., colloidal SiO2, may be used as a low-pH injection grout for very fine fractures in the construction of deep geological repositories for radioactive waste in Sweden and in Finland. If the bentonite barrier encounters SiO2-colloid particles under conditions favorable for aggregation, there is concern that it will modify the bentonite barrier at the bentonite/bedrock interface. In this study qualitative experiments were performed with mixed dispersions of SiO2-colloids and bentonite or homo-ionic Na/Ca-montmorillonite. Samples were prepared at different colloid concentrations and treated under various conditions such as low and high ionic strength (0.3M NaCl), as well as dehydration and redispersing. Free swelling and settling experiments were performed in order to qualitatively compare the conditions in which SiO2-colloids affect the bulk/macro properties of bentonite. In order to study specific SiO2-colloid/montmorillonite interactions and preferred type of initial aggregation, dilute dispersions of homo-ionic montmorillonite dispersions mixed with varying concentrations of SiO2-colloids were prepared and selected samples were characterized by PCS, SEM/EDS, AFM and PXRD. The results from this study show that bentonite and montmorillonite particles can be modified by SiO2-colloids when mixed in comparable amounts, due to dehydration or high ionic strength. Some indications for increased colloidal stability for the SiO2-colloid modified clay particles were also found. From the AFM investigation it was found that initial attachment of the SiO2-colloids in Na+ dominated samples seemed to occur on the edges of the montmorillonite layers. In Ca2+ dominated samples not subjected to excess NaCl, SiO2-colloid sorption onto the faces of the montmorillonite layers was also found. In all, contact between the bentonite barrier and ungelled Silica sol should preferably be avoided. [Copyright &y& Elsevier]

Abstract: The Long Term Test of Buffer Material (LOT) project at the Äspö Hard Rock Laboratory, Sweden, is a series of medium-scale field experiments focused on validating models and hypotheses concerning long term processes in the bentonite buffer of a repository for high-level radioactive waste. The test parcels emplaced in crystalline bedrock consist of blocks of compacted MX80 bentonite embedding a Cu-tube equipped with a heater to simulate the heat generation from radionuclide decay. The A2 test parcel had been subjected to elevated temperature (up to 130°C) and hydration by a Na–Ca–Cl type groundwater for almost 6years when it was retrieved to be analysed. The analyses included determinations of chemical composition, cation exchange capacity (CEC), exchangeable cations and mineralogy. Both the bulk bentonite and dialysed, homo-ionic Na-clay (<2μm and <0.2μm fractions) were analysed when relevant. Sulphate was redistributed in the heated part of the buffer under the thermal and hydration gradients that prevailed during the test period. Anhydrite accumulated in the warmer parts, whereas gypsum was dissolved in the peripheral parts of the buffer where water was supplied. Carbonate dissolution increased with temperature in the warmest parts, whereas chloride behaved conservatively in all blocks. Cu was incorporated in the bentonite matrix at the surface of the Cu-tube indicating some corrosion, which may be explained by reactions in an early stage of the test when trapped oxygen existed in the system. Along with the dissolution/precipitation reactions the porewater composition changed, which resulted in replacement of exchangeable sodium by calcium and magnesium in the warmest zone. Also Mg in the clay (<2μm and <0.2μm fractions) displays a clear gradient with peak values at the heater. Because several of the alternative sinks for Mg were eliminated in the sample preparation prior to the chemical analysis (purified clay fractions, removal of carbonates, Na-saturation) the smectite is suggested a candidate sink for Mg. Parallel with the increase in Mg, a loss in Si is indicated and CEC tends to increase in the clay that had been heated at 130°C. A loss in tetrahedral Si that is balanced by Al, and replacement of Al by Mg in the octahedral sheet would imply that the layer charge of the smectite increased, which would be consistent with the higher CEC values of these samples. The changes in CEC are, however, close to the analytical resolution of the CEC method and no effect of the changes in chemical composition can be detected in the XRD-characteristics of the clay. Therefore, supplementary high-resolution analyses are required to verify whether the structure of montmorillonite has altered in the test period. [Copyright &y& Elsevier]