The Boom Clay in northern Belgium has been studied intensively over recent decades as a potential host rock in the context of disposal of radioactive waste. One of the parameters of interest is the cation exchange capacity (CEC) as it is related to the sorption potential of radionuclides to the clay host rock. In the past, the CEC was determined using various methods on a limited number of samples, leading to significant variations. To constrain the CEC of the Boom Clay better, a sample set covering the entire stratigraphy was measured using the quick copper(II) triethylenetetramine method. Part of the sample set was also measured using the cobalt(III) hexamine method, as a quality control for the results of the former method. In addition, the exchangeable cation population of the Boom Clay was quantified systematically for the first time and these results were compared to the in situ pore-water chemistry, indicating a strong coupling between the pore-water composition and the exchangeable sites of clay minerals.

The evolution of the nitrogen and boron content of shales during diagenesis and anchimetamorphism was studied in the Carboniferous rocks of Donbas by means of the bulk rock chemical analysis and the XRD quantification of mineral composition, aided by CEC and EGME sorption measurements. The contributions of the organic-bound N and B were taken into account, based on the literature data (B) and on the relationship established in the course of this study (N). 28–98% of the total N and 80–100% of the total B are contained in the mineral fraction of the investigated shales.

The mineral nitrogen is located mostly in illite and accounts for 3 to 64% of the sites available for its fixation in 1Md illite. The fixation of N by illite seems to diminish in the course of diagenesis, but additional fixation occurs in newly formed 2M1 illite during the anchimetamorphic stage. The volume of N contained in illite in most samples greatly surpasses the N available locally from the organic matter contained in shale. Modelling indicates that the measured level of N for K substitution in illite corresponds to the capture in 30 vol.% of shale of all N released in a basin containing 5 vol.% of coal.

Boron is held predominantly by the 1Md fraction (illite+smectite). During diagenesis boron is redistributed into the 1Md illite, and during anchimetamorphism it is released from the 1Md illite and incorporated into new 2M1 illite. No indication of the net enrichment of pore water in B due to the clay alteration process was found.

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.

Two 20-cm long columns of MX-80 bentonite compacted at a nominal dry density of 1.7 g/cm3 with a water content of 17% were tested in thermo-hydraulic (TH) cells with the aim of simulating the conditions of a sealing material in a nuclear waste repository. On top of the columns a hydration surface simulated the host rock supplying groundwater and at the bottom a heater simulated the waste canister. The tests comprised two phases: a heating phase and a ‘heating + hydration’ phase. The temperatures at the ends of the columns were set during the last phase to 30°C at the top and 140°C at the bottom, respectively. The thermo-hydraulic treatment resulted in major changes along the bentonite columns. These changes led to significant gradients along the column with respect to the physical state (water content, dry density) and geochemistry of the bentonite. Smectite dissolution processes occurred. As a result, colloids were probably produced, particularly in the more hydrated areas. In the warmest part of the columns precipitation of carbonates took place, caused by their solubility decrease with temperature and the evaporation. The increase in water content reduced the ionic strength of the pore water in the more hydrated areas where species such as gypsum were dissolved. The solubilized ions were transported towards the bottom of the columns; Na+, Ca+, Mg2+ and SO42− moved at a similar rate and K+ and Cl− moved farther. These solubilized ions precipitated in the form of salts farther away along the columns as the test was longer. The TH treatment implied the loss of exchangeable positions in the smectite, particularly towards the heater. The cation exchange complex was also modified.

The Rupel Clay member in the Netherlands largely corresponds to the Boom Formation in Belgium, and this marine, clay-rich deposit is a potential candidate to host radioactive waste disposal facilities. Prediction of the speciation of radionuclides in Rupel Clay pore water and their retardation by interactions with Rupel Clay components requires knowledge about the composition of Rupel Clay pore water, the inventory of reactive solids and understanding of interactions between Rupel Clay and pore water. Here, we studied Rupel Clay material which was obtained from cores collected in the province of Zeeland, the Netherlands, and from drilling cuttings retrieved from a drilling in the province of Limburg, the Netherlands. Pore water was obtained by mechanical squeezing of Rupel Clay material from Zeeland. Additionally, anaerobic dilution experiments were performed in which the clay material was suspended with demineralised water or a 0.1M NaHCO3 solution. Solid-phase characterisation included determination of carbon, nitrogen and sulphur contents, measurement of cation exchange capacity (CEC) and sequential extraction of iron phases.

In contrast to the pore water in Belgian Boom Clay, pore water collected from the location in Zeeland has a higher salinity, with chloride concentrations corresponding to 70–96% of those in seawater. The high chloride concentrations most likely result from the intrusion of ions from saline waters above the Rupel Clay in Zeeland. Cation exchange during salinisation might account for the observed deficit of marine cations (Na, K, Mg) and excess of Ca concentrations, in comparison with seawater. The measured CEC values at both locations in the Netherlands vary between 7 and 35 meq(100g)−1 and are, for most samples, in the range reported for Boom Clay in Belgium (7–30meq(100g)−1).

Pore water and solid-phase composition indicate that Rupel Clay from Zeeland has been affected by oxidation of pyrite or other Fe(II)-containing solids. When coupled to the dissolution of calcium carbonates, oxidation of pyrite can account for the elevated sulphate and calcium concentrations measured in some of the pore waters. The relatively low concentrations of pyrite, organic carbon and calcite in the Rupel Clay in Zeeland, in comparison to Limburg, might be an indicator for an oxidation event. Higher contents of dithionite-extractable Fe in Rupel Clay in Zeeland (0.7–2.6mg Fe / g clay) than in Limburg (0.4–0.5mg Fe / g clay) might also be a consequence of the oxidation of Fe(II) minerals. Oxidation in the past could have accompanied partial erosion of Rupel Clay in Zeeland before deposition of the Breda Formation. However, indications are given that oxidation occurred in some of the pore waters after sampling and that partial oxidation of the cores during storage cannot be excluded. Results from dilution experiments substantiate the influence of equilibration with calcium carbonates on pore water composition. Furthermore, removal of dissolved sulphate upon interaction with Rupel Clay has been observed in some dilution experiments, possibly involving microbial sulphate reduction.

L'influence respective du sédiment et des populations d'huîtres cultivées (Crassostrea gigas) sur l'accumulation et le recyclage des différentes formes de l'azote organique et minéral sont précisées. Les flux d'azote minéral et organique des formes dissoutes de la colonne d'eau, des eaux interstitielles et des eaux susjacentes sont étudiés, ainsi que ceux des formes particulaires représentés par les matièresen suspension, les biodépôts et le sédiment. Le flux annuel de la colonne d'eau d'azote minéral est de 10,5. 106 g.m−2, celui de l'azote organique n'atteint que la moitié. Le flux d'azote particulaire est égal à 15.106 g.m−2.an−1. Par contre l'azote phytoplanctonique ne représente que 6 % de l'azote particulaire total. Ceci souligne l'origine détritique de la matiére organique de cet écosystème. Dans les zones de cultures, l'accumulation d'azote est de 94 g.m−2.an−1, alors qu'elle n'est que de 15 g.m−2 . an−1 dans les zones témoins. Les flux d'azote minéral dissous en provenance du sédiment sont plus élevés sous les cultures (23 g.m−2.an−1) que dans le sédiment témoin (15 g.m−2.an−1). Une culture d'huîtres induit une fixation supplémentaire d'azote de 71 g.m−2.an −1. Deux comportements saisonniers caractérisent cet écosystème : (i) de forts apports hivernaux de nitrates par la colonne d'eau et leur absorption au niveau du sédiment, accompagnés d'une forte production de biodépôts; (ii) un relargage printanier et automnal d'ammonium par le sédiment en présence d'azote organique abondant dans la colonne d'eau.