Municipal solid waste incinerator (MSWI) bottom ash is the slag-like material produced by the incineration of municipal waste and is predominantly composed of glassy constituents, which include inherited manufactured glasses and glasses formed during incineration. Previous results indicate evidence of neoformation of well-ordered clay (illite) from glasses in MSWI bottom ash after 12 y of natural weathering. We investigated the mechanism and conditions of clay formation from glasses during natural weathering using transmission electron microscopy (TEM), experimental leaching experiments and ammonium oxalate extractions. It was concluded that the high surface area and initially high “active” Al and associated Si content predispose the ash to form clay minerals on a relatively short time scale. This work provides evidence that the composition of secondary amorphous aluminosilicate and thus, the type of clay mineral which may form, is determined by the pH of the pore solution rather than by the glass composition. Presumably alternate wetting and drying of the ash during disposal greatly accelerates the formation of well-ordered clays.

Argillaceous rocks are considered to be a suitable geological barrier for the long-term containment of wastes. Their efficiency at retarding contaminant migration is assessed using reactive-transport experiments and modeling, the latter requiring a sound understanding of pore-water chemistry. The building of a pore-water model, which is mandatory for laboratory experiments mimicking in situ conditions, requires a detailed knowledge of the rock mineralogy and of minerals at equilibrium with present-day pore waters. Using a combination of petrological, mineralogical, and isotopic studies, the present study focused on the reduced Opalinus Clay formation (Fm) of the Benken borehole (30 km north of Zurich) which is intended for nuclear-waste disposal in Switzerland. A diagenetic sequence is proposed, which serves as a basis for determining the minerals stable in the formation and their textural relationships. Early cementation of dominant calcite, rare dolomite, and pyrite formed by bacterial sulfate reduction, was followed by formation of iron-rich calcite, ankerite, siderite, glauconite, (Ba, Sr) sulfates, and traces of sphalerite and galena. The distribution and abundance of siderite depends heavily on the depositional environment (and consequently on the water column). Benken sediment deposition during Aalenian times corresponds to an offshore environment with the early formation of siderite concretions at the water/sediment interface at the fluctuating boundary between the suboxic iron reduction and the sulfate reduction zones. Diagenetic minerals (carbonates except dolomite, sulfates, silicates) remained stable from their formation to the present. Based on these mineralogical and geochemical data, the mineral assemblage previously used for the geochemical model of the pore waters at Mont Terri may be applied to Benken without significant changes. These further investigations demonstrate the need for detailed mineralogical and geochemical study to refine the model of pore-water chemistry in a clay formation.

Corrosion of steel canisters, disposed of in a repository for high-level waste (HLW), leads to generation of hydrogen gas for a long period after the repository's closure. The accumulation of hydrogen gas may lead to significant desaturation and unacceptable build-up of pressure in the backfilled disposal tunnels if the gas cannot escape through the low-permeability host rock. Consequently, the investigation of gas migration is of high relevance in the assessment of the repository's performance.

In this paper, the results of numerical investigations on gas migration performed using the computer code TOUGH2 (USA) are presented. The objective was to investigate migration of gas generated in a single disposal tunnel of a conceptual geological repository in a clay formation, which was suggested for benchmark studies in the European Commission project FORGE (Fate Of Repository GasEs). The analysis was focused on evaluation of the impact of an initial temperature in the repository and of different tortuosity models on gas migration. It was revealed that gas migration results were dependent on tortuosity model, while temperature variation in the repository had minor impact.