Design of a 2-D Cementation Experiment in Porous Medium Using Numerical Simulation

International audienceThe validation and qualification of reactive transport simulation tools has motivated the design and simulation, at a laboratory scale, of an experiment in which flow, advective/dispersive transport of solutes and physicochemical transformation affecting a porous medium are strongly coupled. Several possible experimental setups (or designs) have been evaluated using numerical simulation. The selected experimental design involves the successive precipitation and perforation of a clogging obstacle composed of calcium oxalate. Before an experiment can actually be conducted, this problem is proposed as a numerical benchmark for reactive transport codes and simulated using the coupled reactive transport code Hytec (CIG-École des mines, France)

Evaluating sealing efficiency of caprocks for CO2 storage: an overview of the Geocarbone Integrity program and results

8 pagesInternational audienceThe objectives of the Geocarbone-Integrity program are to develop techniques, methodologies and knowledge concerning the long term confinement of CO2 in geological storage. Linked to other French programs such as Geocarbone Injectivity or Picoref, it is an integrated approach involving geochemistry, petrophysics, geology and geomechanics. Different scales must be considered in order to describe caprocks: from the pore or grain scale in petrophysics and geochemistry, to regional scale in geology and geomechanics. The program focused on a specific site of the Paris basin but the methodologies developed are general and can be applied elsewhere

Impact of the substitution distribution and the interlayer distance on both the surface energy and the hydration energy for Pb-montmorillonite

International audienceThe understanding of the adsorption of charged species in swelling clays is of primary importance to optimise the capture of heavy metal ions in soils. Adsorption is expected to depend on the microscopic structure of the clay, which varies strongly with the origin and history (hydration-desorption cycles, temperature ...) of the sample. Then it is necessary to evaluate the distinct interaction energies between water molecules, interlayer cations and clay surfaces, taking into account the position of the substitutions in the clay layer. Here we propose an investigation of plausible structures of some Pb-montmorillonites differing by their interlayer distances, their layer charges and the distribution of substitutions in octahedral sheet from a modelling approach, looking at the evolution of the partial charges in these structures. Using a methodology previously developed in the simpler case of alkali cations, we also estimate the surface energy in the dry state and then the details of the hydration energy for the cation and for the clay layer to interpret the capacity of ion adsorption in swelling clays to capture heavy metals. We conclude from our calculations that a cell structure with intermediate layer charge (close to 0.5 per unit cell) is probably the best candidate to allow the capture of the Pb2+ as interlayer cations considering the electrostatic effect. The hydration process of the cation appears as the most energetic part of the hydration of swelling clays compared to the interactions with the layer, but the cation mobility is limited since the hydration process is not complete. This means that the heavy metal ions, present in the interlayer space, will be unable to diffuse and will be captured in the case of a low layer charge

Combined geochemical and electrochemical methodology to quantify corrosion of carbon steel by bacterial activity.

International audienceThe availability of respiratory substrates, such as H2 and Fe(II,III) solid corrosion products within nuclear waste repository, will sustain the activities of hydrogen-oxidizing bacteria (HOB) and iron-reducing bacteria (IRB). This may have a direct effect on the rate of carbon steel corrosion. This study investigates the effects of Shewanella oneidensis (an HOB and IRB model organism) on the corrosion rate by looking at carbon steel dissolution in the presence of H2 as the sole electron donor. Bacterial effect is evaluated by means of geochemical and electrochemical techniques. Both showed that the corrosion rate is enhanced by a factor of 2-3 in the presence of bacteria. The geochemical experiments indicated that the composition and crystallinity of the solid corrosion products (magnetite and vivianite) are modified by bacteria. Moreover, the electrochemical experiments evidenced that the bacterial activity can be stimulated when H2 is generated in a small confinement volume. In this case, a higher corrosion rate and mineralization (vivianite) on the carbon steel surface were observed. The results suggest that the mechanism likely to influence the corrosion rate is the bioreduction of Fe(III) from magnetite coupled to the H2 oxidation

Presumed killers? Vultures, stakeholders, misperceptions, and fake news

Vultures and condors are among the most threatened avian species in the world due to the impacts of human activities. Negative perceptions can contribute to these threats as some vulture species have been historically blamed for killing livestock. This perception of conflict has increased in recent years, associated with a viral spread of partial and biased information through social media and despite limited empirical support for these assertions. Here, we highlight that magnifying infrequent events of livestock being injured by vultures through publically shared videos or biased news items negatively impact efforts to conserve threatened populations of avian scavengers. We encourage environmental agencies, researchers, and practitioners to evaluate the reliability, frequency, and context of reports of vulture predation, weighing those results against the diverse and valuable contributions of vultures to environmental health and human well-being. We also encourage the development of awareness campaigns and improved livestock management practices, including commonly available nonlethal deterrence strategies, if needed. These actions are urgently required to allow the development of a more effective conservation strategy for vultures worldwide.Peer reviewe

Diurnal timing of nonmigratory movement by birds: the importance of foraging spatial scales

Timing of activity can reveal an organism's efforts to optimize foraging either by minimizing energy loss through passive movement or by maximizing energetic gain through foraging. Here, we assess whether signals of either of these strategies are detectable in the timing of activity of daily, local movements by birds. We compare the similarities of timing of movement activity among species using six temporal variables: start of activity relative to sunrise, end of activity relative to sunset, relative speed at midday, number of movement bouts, bout duration and proportion of active daytime hours. We test for the influence of flight mode and foraging habitat on the timing of movement activity across avian guilds. We used 64 570 days of GPS movement data collected between 2002 and 2019 for local (non‐migratory) movements of 991 birds from 49 species, representing 14 orders. Dissimilarity among daily activity patterns was best explained by flight mode. Terrestrial soaring birds began activity later and stopped activity earlier than pelagic soaring or flapping birds. Broad‐scale foraging habitat explained less of the clustering patterns because of divergent timing of active periods of pelagic surface and diving foragers. Among pelagic birds, surface foragers were active throughout all 24 hrs of the day while diving foragers matched their active hours more closely to daylight hours. Pelagic surface foragers also had the greatest daily foraging distances, which was consistent with their daytime activity patterns. This study demonstrates that flight mode and foraging habitat influence temporal patterns of daily movement activity of birds.We thank the Nature Conservancy, the Bailey Wildlife Foundation, the Bluestone Foundation, the Ocean View Foundation, Biodiversity Research Institute, the Maine Outdoor Heritage Fund, the Davis Conservation Foundation and The U.S. Department of Energy (DE‐EE0005362), and the Darwin Initiative (19-026), EDP S.A. ‘Fundação para a Biodiversidade’ and the Portuguese Foundation for Science and Technology (FCT) (DL57/2019/CP 1440/CT 0021), Enterprise St Helena (ESH), Friends of National Zoo Conservation Research Grant Program and Conservation Nation, ConocoPhillips Global Signature Program, Maryland Department of Natural Resources, Cellular Tracking Technologies and Hawk Mountain Sanctuary for providing funding and in-kind support for the GPS data used in our analyses

Rétention chimique du Cs par échange d'ions sur l'illite, la vermiculite et la montmorillonite.

International audienceDans le contexte de la surveillance et d'évaluation de l'impact environnemental des sites nucléaires, le comportement des radionucléides dans les sols, les sédiments et les aquifères doit être appréhendé. La migration des éléments en trace est en partie régie par des phénomènes de rétention chimique sur les surfaces minérales, en particulier sur les minéraux argileux connus pour avoir des charges de surface négatives compensées par des cations. Suite aux accidents de Tchernobyl et de Fukushima, de nombreuses études ont été dédiées à la compréhension et à la modélisation du comportement du Cs dans les milieux naturels. Dans ce but, les modèles thermodynamiques de sorption considèrent les processus de sorption comme des phénomènes d'échange d'ions ou de complexation de surface [1-4]. Un modèle d'échangeur d'ions multi-sites [1] utilisant la propriété d'adsorption de phases pures comme la montmorillonite et l'illite, a permis de décrire avec succès l'adsorption du Cs dans un grès argileux dans des conditions statiques [2]. Les données des expériences d'adsorption sont exprimées en courbes de saturation et en isothermes de concentration et de pH. Dans cette approche macroscopique, les sites de sorption sont décrits par leurs capacités de sorption (exprimées en mol/kg de phase solide) et leur affinité vis-à-vis des éléments majeurs et en traces. Des sites de sorption spécifiques sont reconnus pour leur grande affinité pour le Cs sur la smectite, l'illite [2-4] et la vermiculite. Toute affectation structurale des sites de sorption est cependant impossible par cette seule approche. Par ailleurs, cette approche thermodynamique permet d'évaluer la réversibilité du processus d'adsorption. Cette réversibilité de l'équilibre chimique est cependant peu étudiée. Elle fait fréquemment référence à une désorption dans un contexte physico-chimique différent des conditions d'adsorption [5]. De ce fait, la réversibilité d'adsorption du Cs sur l'illite et sur la vermiculite reste controversée.Au regard de résultats récents d'adsorption/ désorption du Cs sur l'illite et la vermiculite calciques ainsi que de mesures de la distance de la raie (001) par DRX, la réversibilité d'adsorption du Cs sur ces deux minéraux est discutée. Les comportements du Cs sur l'illite, la vermiculite et la smectite sont comparés

RTM for Waste Repositories

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Gas-Water-Rock Interactions Induced by Reservoir Exploitation, CO2 Sequestration, and Other Geological Storage

International audienceAt the opening of the Millenium the planet Earth is confronted with a major open question, namely: what will be the result in the nearby future of the soaring interference between human activities and natural environmental processes? There is an increasing sense of alarm about the anthropogenic threats that exert pressure on the environment, especially if projected towards the future with the growing adoption of the standards of leaving that prevail in developed countries. Modern economies, born from the Industrial Revolution, have developed on the basis of the largely available and relatively inexpensive energy provided by fossil fuels, which are easy to produce, to transport, to store and to use in concentrated power units. In the so-called rich countries basic equipment, energy production means, industrial facilities, lifestyle expectations were shaped by this position with respect to energy, and fastly developing countries today reproduce the same attitude. But for the first time in human history the rising population, the escalating consumption of energy, water, food and raw materials, the increasing production of substances and goods but also of pollutants and wastes, and the expanding demand for mobility and transportation collide with the physical capacities of the planet's resources

Guest editorial to the special issue: subsurface environmental simulation benchmarks

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