[en] Mining of the Pueblo Viejo high-sulphidation epithermal deposit (Dominican Republic) leads to environmental impact due to the formation of acid mine drainage associated with the oxidative dissolution of sulphides and sulpho salts. In addition to the very low pH, the acid waters are capable of transporting away from the mining areas high concentrations of metals and metalloids in solution. In the present work, a geochemical study of sediments deposited in the Hatillo reservoir is carried out. This reservoir is fed by the Margajita and Yuna streams which transport leachates from the Pueblo Viejo and Falcondo-Bonao (Cr-Ni) mining areas, respectively. The results show that these sediments have very high concentrations of Fe, Al and sulphate, along with significant amounts of As, Zn and Te, which are of especial environmental concern. The main contributor to this metal discharge into the reservoir is the Margajita stream, whereas the Yuna stream does not transport significant amounts of metals in solution due to its neutral pH, although it is likely that metals such as Mn, Cr, Ni and Co can be mobilised as a particulate. (Author) 5 refs.

[en] This report discusses in a quantitative manner the evolution of the near field aqueous chemistry as a result of the interactions between three different intruding groundwaters (Aespoe, Gideaa and Finnsjoen) with the MX-80 bentonite buffer material. The main emphasis has been placed on studying the evolution of the main chemical buffers of the system (alkalinity and redox capacities) and the resulting master variables (pH and pe). The calculations have been done by using a set of thermodynamic and kinetic parameters previously calibrated against experimental data on bentonite/granitic groundwater interactions, in combination with the PHREEQC geochemical code. The results of the calculations indicate that the alkalinity buffer capacity is mainly exerted by the accessory content of carbonate minerals (calcite) in the bentonite system, while the ion exchange process plays a secondary (but not negligible) role. The Ca(II) content of the intruding groundwater has an impact on the resulting pH. For Ca(II) rich waters, like Aespoe, the resulting pH remains in the range of granitic groundwaters (7.5-9.5) during the overall repository lifetime (1 million years). For Ca(II) poor groundwaters, the systems evolves to high alkalinity (pH : 10.5 - 10.8) due to the depletion of calcite and the release of carbonate in to the near field aqueous chemistry. Concerning the reducing capacity of the system, this is mainly controlled by the accessory pyrite content, although the Fe(II) content in montmorillonite and in the carbonates cannot be disregarded. Reducing conditions in the bentonite/groundwater system are ensured throughout the lifetime of the repository system unless this is placed in direct and lifetime contact with the atmosphere (surface storage)

[en] In order to explain the higher bioactivity of the silicon-substituted hydroxyapatite (SiHA), synthetic ceramic hydroxyapatite (HA) and SiHA have been structurally studied by neutron scattering. The Rietveld refinements show that the final compounds are oxy-hydroxyapatites, when are obtained by solid-state synthesis under air atmosphere. By using neutron diffraction, the substitution of P by Si into the apatite structure has been corroborated in these compounds. Moreover, these studies also allow us to explain the better bioactive behavior of SiHA, in terms of a higher thermal displacement parameters of the H located at the 4e site

[en] This report discusses in a quantitative manner the evolution of the near field geochemistry as a result of the interactions between two different introducing granitic groundwaters and the FEBEX bentonite as a buffer material. The two granitic groundwaters considered are: SR-5 water, sampled in a borehole at 500 m depth in Mina Ratones, and a mean composition of different granitic groundwaters from the iberian Massif. The steel canister has also been introduced by considering the iron corrosion in anoxic conditions. (Author)

[en] The concept for the final disposal of spent nuclear fuel in Finland considers an engineered and natural (crystalline rock) multi-barrier system surrounding the spent fuel. This work aims at predicting and making a quantitative assessment of the geochemical evolution of the near-field (canister, buffer, backfill and adjacent fractured bedrock) during the unsaturated thermal period and in the long-term, after saturation has been completed. The groundwater/bentonite buffer interaction during the unsaturated thermal period is tackled through a two-dimensional (2D) axisymmetric scheme using the thermo-hydro-geochemical code TOUGHREACT. In turn, the long-term interaction of the fully water-saturated buffer and backfill with groundwater is assessed through 3D numerical models using the reactive transport code PHAST under isothermal conditions. A set of base cases have been set up based on the most plausible set of input data. In addition, a limited number of sensitivity cases have been conducted to analyse the influence of key parameters controlling the system and reduce uncertainty. Predicted mineralogical changes of accessory minerals in the bentonite for the thermal period are controlled by the dependence of mineral solubilities on temperature and on the solute transport by advection during the saturation process, and diffusion during the whole period. The results of the thermal period indicate that a small amount of the primary amorphous silica is redistributed in the buffer: dissolution close to the canister and precipitation close to the buffer - rock interface. Primary calcite dissolution/precipitation is minimal, remaining stable throughout the simulation time in all cases. Anhydrite precipitates near the canister due to the elevated temperature, while it dissolves from the outside of the buffer. The results indicate that there is no significant evaporation of water near the copper canister and thus no chloride salt reaches saturation. The geochemical changes of the buffer in the long-term are also limited. Complete dissolution of gypsum from the buffer is predicted in some cases. The changes in the montmorillonite exchanger are significant, with a high replacement of sodium and magnesium by calcium. The inflow of Olkiluoto groundwater leads to relatively small changes on the pH of the near-field. Overall, the models indicate that the buffer will remain geochemically stable throughout the simulation time for the conditions considered in this work. (orig.)

[en] Document available in extended abstract form only. In the KBS-3 concept for the nuclear waste repository, designed by the Swedish Nuclear Fuel and Waste Management Co. (SKB), the bentonite buffer is placed around the copper canisters that contain the spent nuclear fuel, isolating it of the host rock. In order to check - hypotheses for the evolution of the bentonite buffer under the thermo-hydraulic conditions expected in a KBS-3 repository, SKB is conducting a series of long term buffer material (LOT) tests at the Aespoe Hard Rock Laboratory (HRL). In the present work, numerical simulations are developed to simulate: i) thermo-hydraulic processes; ii) geochemical reactions and; iii) transport of solutes, that have been measured in the LOT A2 test, and, that are expected in the near-field of a KBS-3 repository. The numerical model for the LOT A2 test is based on analytical results and on field-scale experiments. The validation of this model allows us to implement it for the thermal period of the near field of the KBS-3 repository, based on previous modelling exercises. During the operation of a KBS-3 repository (after deposition of the copper canisters), the unsaturated bentonite will be submitted to a relatively high thermal gradient, induced by the radioactive decay of the spent nuclear fuel. On the other hand, the saturated host rock will provide aqueous solution to the unsaturated bentonite, induced by differential hydraulic pressures, under specific thermal and mechanic conditions. In this context, the bentonite will gradually become fully water saturated. Experimental results indicate that during the saturation period, the transport of solutes in the bentonite buffer will be influenced by water uptake from the surrounding host rock towards the wetting front, and also by a cyclic evaporation/condensation process, induced by the thermal gradient. Our numerical models take into account the transport of solutes and geochemical reactions under nonisothermal conditions, and in a scenario of variable pore water saturation. The reference groundwater composition that represents the host rock groundwater (mainly located in fractures) is taken from a borehole drilled in the Aespoe HRL that supplied the LOT A2 test. The initial pore water composition of the bentonite buffer is based on the experimental results attained in Karnland et al. (2008). From the mineralogical description of the MX-80 bentonite, and under the pH and redox conditions expected for the near-field of the future KBS-3 repository, the main reactive minerals of the bentonite buffer are montmorillonite, gypsum and pyrite. In terms of its solubility, montmorillonite seems to remain relatively stable under the geochemical and thermo-hydraulic conditions of a KBS-3 repository, and therefore, it only participates in cation exchange reactions. Finally, from the results attained in previous works, anhydrite and calcite are let to precipitate if over-saturation is reached. The numerical model developed for the LOT A2 test indicates that the bentonite buffer is fully water saturated within the first half-year which is in agreement with measured data. Numerical results indicate that, despite the evaporation/condensation cycling, the chloride transported by the flow of Aespoe groundwater into the bentonite buffer behaves conservatively (no chloride salts precipitate). In addition, numerical results indicate that the behaviour of anhydrite, gypsum and calcite is influenced by the thermal gradient that is established during the saturation period of the bentonite buffer. (authors)

[en] The main aquifer of Delta del Llobregat (Barcelona, Spain) is affected by seawater intrusion from 1970. For stopping its advance, the Catalan Water Agency is carrying out the construction of a positive hydraulic barrier through the injection of water in 14 wells. This is the first project of these characteristic that it is carried out in Spain and pioneer in Europe. The barrier elevates the groundwater level of the aquifer near the coast and avoids that the seawater penetrates inland, using reclaimed water of Baix Llobregat WWTP with several treatments. The first phase brings already more than 2 years of functioning, with highly positive results since a substantial improvement of the quality of the groundwater has been observed. The second phase is at present under construction. (Author)

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