Impact of a 70°C temperature on an ordinary Portland cement paste/claystone interface: An in situ experiment

International audienceRadioactive wastes in future underground disposal sites will induce a temperature increase at the interface between the cementitious materials and the host rock. To understand the evolution of Portland cement in this environment, an in situ specific device was developed in the Underground Research Laboratory in Tournemire (France). OPC cement paste was put into contact with clayey rock under water-saturated conditions at 70°C. The initial temperature increase led to ettringite dissolution and siliceous katoite precipitation, without monosulfoaluminate formation. After one year of interaction, partial decalcification and diffuse carbonation (calcite precipitation) was observed over 800 μm in the cement paste. At the interface, a layer constituted of phillipsite (zeolite), tobermorite (well-crystallised C-S-H), and C-(A)-S-H had formed. Globally, porosity decreased at both sides of the interface. Geochemical modelling supports the experimental results, especially the coexistence of tobermorite and phillipsite at 70°C, minerals never observed before in concrete/clay interface experiments

Determination of elastic modulus of claystone: Nano-/micro-indentation and meso-compression tests used to investigate impact of alkaline fluid propagation over 18 years

Micro-mechanical properties of a claystone were tested after undergoing alkaline perturbation on site (Tournemire, CD borehole) for 18 years. In a saturated context and outside the excavation disturbed zone (EDZ), the claystone exhibits a 11.6-mm black rim at the cement/paste interface, which shows a different mechanical behaviour from the rest of the claystone. Three sets of measurements of elastic modulus were performed using: (i) nano-indentation tests with a constant indentation depth of 2 μm, (ii) micro-indentation tests with a constant indentation depth of 20 μm, and (iii) meso-compression tests with a constant displacement of 200 μm. The increase of the modulus of deformability in the black rim is between 15 GPa and 20 GPa according to the scale. Moreover, an overall decrease of the modulus of deformability from the smallest to the largest scale is observed in each zone. In view of the mineralogy and petrographic observations, higher values of modulus of deformability in the black rim are related to carbonate content and its distribution. Precipitation of cementitious carbonates as inclusions and very thin partings leads to hardening of the claystone

Elastic modulus of claystone evaluated by nano-/micro-indentation tests and meso-compression tests

Toarcian claystone such as that of the Callovo-Oxfordian is a qualified multiphase material. The claystone samples tested in this study are composed of four main mineral phases: silicates (clay minerals, quartz, feldspars, micas) (≈86%), sulphides (pyrite) (≈3%), carbonates (calcite, dolomite) (≈10%) and organic kerogen (≈1%). Three sets of measurements of the modulus of deformability were compared as determined in (i) nano-indentation tests with a constant indentation depth of 2 μm, (ii) micro-indentation tests with a constant indentation depth of 20 μm, and (iii) meso-compression tests with a constant displacement of 200 μm. These three experimental methods have already been validated in earlier studies. The main objective of this study is to demonstrate the influence of the scaling effect on the modulus of deformability of the material. Different frequency distributions of the modulus of deformability were obtained at the different sample scales: (i) in nano-indentation tests, the distribution was spread between 15 GPa and 90 GPa and contained one peak at 34 GPa and another at 51 GPa; (ii) in the micro-indentation tests, the distribution was spread between 25 GPa and 60 GPa and displayed peaks at 26 GPa and 37 GPa; and (iii) in the meso-compression tests, a narrow frequency distribution was obtained, ranging from 25 GPa to 50 GPa and with a maximum at around 35 GPa

Les conséquences de la guerre sur l'évolution des paysages et des sols à Flirey, à l'est du Saillant de Saint-Mihiel

National audienc

Géoarchéologie d’un secteur de combat de la Guerre des mines dans le Saillant de St Mihiel (Première Guerre Mondiale, communes de Flirey et Seicheprey)

International audienc

Insight into the Extractive Metallurgy of Tin from Cassiterite

International audienceThis review details both the conventional and emerging methods of extracting tin from cassiterite. The emerging methods reviewed include sulphuric acid leaching of SnO, cooling crystallization of SnO, sulphide leaching, alkaline leaching, and dry chlorination. From these methods, the conventional approach (direct reduction smelting) stands out as the sole method that is suitable for industrial application, with none of the emerging ones being promising enough to be a contender. The thermodynamics involved in the hydrometallurgical extraction of tin from the mineral are also discussed. ΔGo values calculated at 25 °C for the reduction–dissolution of SnO2 using reducing gases revealed feasibility only when carbon monoxide was used. An indication of the possible species produced during the hydrolysis of the oxide of the metal (SnO2 and SnO) as a function of pH (ranging from −2 to 14 and 0 to 14 for SnO2 and SnO, respectively) was noted and highlighted to link a Pourbaix diagram generated from literature data. This diagram suggests that the solubility of SnO2 in both strongly acidic and alkaline media is possible, but with a small dissolution window in each. The purification and recovery routes of the various processing techniques were then envisaged