Dans la région de Trois-Rivières, de nombreuses résidences ont été construites sur une fondation de béton incorporant des granulats riches en sulfures de fer, notamment de la pyrrhotite et de la pyrite. Plus de trois cents échantillons ont été prélevés au sein de seize fondations de maisons montrant différents degrés d’endommagement, de très faible à très élevé, afin de les analyser et de contribuer à une meilleure compréhension des mécanismes en cause. Plusieurs types d’essais pétrographiques, mécaniques et chimiques ont ainsi été effectués sur ces échantillons, tant sur le terrain qu’en laboratoire. Le suivi de l’expansion et du développement de la fissuration sur des blocs prélevés au sein de fondations résidentielles a permis de démontrer le potentiel résiduel d’endommagement du béton lorsque soumis aux conditions climatiques naturelles. De plus, les résultats des travaux effectués sur les blocs suggèrent que la méthode de l’indice de fissuration est un bon outil du suivi l’évolution de l’endommagement du béton. Finalement, les résultats des travaux effectués en laboratoire suggèrent que le Damage Rating Index et le Stiffness Damage Test ont la capacité de quantifier l’état d’endommagement des bétons détériorés fabriqués avec des granulats incorporant des sulfures de fer. / In the Trois-Rivières area, many houses were built on a concrete foundation made with aggregates containing large amounts of iron sulfides, such as pyrrhotite and pyrite. To allow for a better understanding of the oxidation mechanism, more than three hundred samples were extracted from sixteen foundations, showing different degrees of damage. A variety of petrographic, mechanical and chemical tests were conducted on these samples, in the laboratory as well as in the field. The monitoring of the development of expansion and cracking in the concrete blocks taken from residential foundations demonstrated a potential for residual concrete deterioration when exposed to natural environmental conditions. Furthermore, results of experiments performed on the blocks suggest that the cracking index method is a good indicator of the evolution of damage. Finally, laboratory testing suggests that the Damage Rating Index and the Stiffness Damage Test can potentially quantify damage suffered by deteriorated concrete made with aggregates incorporating iron sulfide minerals.

La déshydratation, l’oxydation et la fracturation sont les trois principaux processus couplés subis par l’argilite callovo-oxfordienne recoupée par les galeries du Laboratoire Souterrain de Meuse/Haute-Marne de l'Andra lors de l'excavation de galeries. Une série de forages à différents temps après l'ouverture de la galerie a permis d'étudier l'évolution des perturbations en fonction du temps, jusqu'à 18 mois. Les profils de teneur en eau et les analyses isotopiques montrent une déshydratation en surface des parois d'environ 50%. Le front de déshydratation est rapidement sub-stationnaire car il résulte d'un équilibre entre la recharge par l'eau de la formation et l'évaporation imposée par la pression partielle de l'eau dans l'air de la galerie. La zone perturbée affecte principalement les premiers 70 cm, et ne se fait plus sentir à partir de 1 m 50. L’oxydation des pyrites provoque la formation de fluides sulfatés acides qui dissolvent les minéraux environnants, libèrent dans la solution des ions Ca2+, K+ et Na+ puis lors de la déshydratation de l’argilite, l'évaporation de l'eau porale induit la précipitation de minéraux sulfatés principalement. La dégradation de la matière organique dans les conditions des galeries montre une dégradation limitée, due soit à une oxydation très discrète, soit à une dégradation lente non détectable aux temps courts. Une série d'expérience de mise en équilibre d'eau avec une roche plus ou moins oxydée a permis d'évaluer l'impact de la présence des phases minérales néoformées sur les caractéristiques chimiques des eaux de réhydratation. Cette approche expérimentale a été confrontée aux résultats de modélisation géochimique. Les résultats obtenus permettent de mieux préciser les caractéristiques géométriques, minéralogiques et physico-chimiques de cette zone perturbée qui est susceptible d'évoluer par la suite en condition de réhydratation et d'élévation de température lors du stockage / Dehydration, oxidation, and fracturing are the three main and coupled processes underwent by Callovian-Oxfordian argillite cut by the galleries of the Laboratoire Souterrain of Meuse / Haute-Marne of Andra during the excavation. Several boreholes drilled at different times after the opening of the gallery were used to study the evolution of disturbances with time up to 18 months. Profiles of water content and isotopic analysis show dehydration at the surface of the walls of about 50%. The area of dehydration is rapidly sub-stationary because it results from a balance between the suction by the pore water and the evaporation imposed by the partial pressure of water in the air of the gallery. The disturbed area mainly affects the first 70 cm, and not exceeds 1 m 50. The oxidation of pyrite causes the formation of acid sulphate fluids which dissolve the surrounding minerals in the solution, release Ca2+, K+ and Na+ in the pore water then during the dehydration of argillite, the evaporation of the pore water leads to the precipitation of sulphate minerals mainly. The degradation of organic matter in the galleries shows a limited deterioration due to a very moderate oxidation or the slow degradation is not detectable at short times. Several experiments of equilibration between more or less oxidized samples and water were used to evaluate the impact of the presence of new-formed mineral phases (sulphates) on the chemical composition of the rehydration water. This experimental approach has been compared to results of geochemical modelling. The results obtained allow us to define geometrical, mineralogical and physico-chemical properties of the disturbed zone which could evolve thereafter during rehydration and temperature rise in storage condition

Afin de cartographier la structure souterraine des volcans et détecter des ressources géothermiques de haute température, on utilise souvent l’imagerie de résistivité électrique. La résistivité électrique des volcans est affectée par plusieurs facteurs: volume et salinité de l’eau interstitielle, abondance de minéraux conducteurs, température de la roche et présence de magma. Ce travail de thèse tente de contraindre l'interprétation des structures de résistivité électrique autour des volcans actifs, afin de développer des outils innovants pour l'exploration des ressources géothermiques. La contribution des minéraux conducteurs est au cœur de la thèse: conducteurs ioniques solides (minéraux argileux, en particulier la smectite) ou semi-conducteurs électroniques (pyrite, oxydes de fer), mais l’influence de la porosité, de la salinité, de la température et de la présence de magma est aussi étudiée. La thèse utilise le volcan Krafla comme terrain d’étude pour affiner les interprétations des structures de résistivité électriques, du fait de la disponibilité de carottes, de données, de bibliographie et d’infrastructure. La smectite et la pyrite sont formées par altération hydrothermale des roches volcaniques et témoignent ainsi des convections hydrothermales. Les oxydes de fer en revanche sont plutôt formés lors de la cristallisation du magma et sont dissous lors des circulations hydrothermales. La contribution de la smectite à la conductivité électrique de roches volcaniques, saturées en eau à différentes salinités, est d'abord étudiée en laboratoire (à température ambiante) par spectroscopie d’impédance électrique « résistivité complexe ». Des variations non linéaires de la conductivité électrique à 1 kHz avec la salinité sont observées et discutées. La conduction interfoliaire est suggérée comme un mécanisme important par lequel la smectite conduit le courant électrique. L'influence de la pyrite et des oxydes de fer sur les effets de polarisation provoquée est ensuite analysée en utilisant l'angle de phase de l'impédance, qui dépend de la fréquence. Un angle de phase maximal supérieur à 20 mrad est attribué à la pyrite si la roche est conductrice et aux oxydes de fer si la roche est résistive. L'angle de phase maximal augmente d'environ 22 mrad pour chaque pourcent de pyrite ou d'oxyde de fer. Ces résultats de laboratoire en domaine fréquentiel sont appliqués à l’interprétation de tomographies de résistivité complexe sur le terrain en domaine temporel. Smectite, pyrite et oxydes de fer ont pu être identifiés jusqu'à 200 m de profondeur. La température in-situ, plus élevées qu’en laboratoire, semble augmenter la conductivité de la smectite. De manière générale, la tomographie de résistivité complexe est recommandée comme méthode complémentaire aux sondages électromagnétiques pour l'exploration géothermique. / Electromagnetic soundings are widely used to image the underground structure of volcanoes and look for hightemperature geothermal resources. The electrical resistivity of volcanoes is affected by several characteristics of rocks: volume and salinity of pore fluid, abundance of conductive minerals, rock temperature and presence of magma. This thesis aims at improving the interpretation of electrical resistivity structures around active volcanoes, in order to develop innovative tools for the assessment of geothermal resources. I focus on conductive minerals, which can either be solid ionic conductors (clay minerals, in particular smectite) or electronic semi-conductors (pyrite and iron-oxides), but I also investigate the effects of porosity, salinity, temperature and presence of magma. I use Krafla volcano as a laboratory area, where extensive literature, borehole data, core samples, surface soundings and infrastructures are available. Smectite and pyrite are formed upon hydrothermal alteration of volcanic rocks and thus witness hydrothermal convection. On the other hand, iron-oxides are mostly formed during the primary crystallization of magma and dissolved by hydrothermal fluids. The contribution of smectite to the electrical conductivity of volcanic rocks saturated with pore water at different salinity is first investigated in the laboratory (room temperature) by electrical impedance spectroscopy “complex resistivity”. Non-linear variations of the conductivity at 1 kHz with salinity are observed and discussed. Interfoliar conduction is suggested as an important mechanism by which smectite conducts electrical current. The influence of pyrite and iron-oxides on induced polarization effects is then analyzed, using the frequency-dependent phase-angle of the impedance. A maximum phase-angle higher than 20 mrad is attributed to pyrite if the rock is conductive and to ironoxides if the rock is resistive. The maximum phase-angle increases by about 22 mrad for each additional per cent of pyrite or iron-oxide. These laboratory frequency-domain findings are partly upscaled to interpret field time-domain complex resistivity tomography at Krafla: smectite, pyrite and iron-oxides can be identified down to 200 m. The in-situ temperature, higher than in laboratory conditions, appears to significantly increase the conductivity associated to smectite. In general, time-domain complex resistivity measurements are recommended as a complementary method to electromagnetic soundings for geothermal exploration.

Pressure oxidation of refractory gold ores containing carbonate minerals is conducted under neutral/alkaline conditions in order to promote fast kinetics, reduced reagent consumption and suppressing the formation of elemental sulphur and CO2 (which reduces the effectiveness of the process). In this work, both the addition of sodium carbonate and the presence of silica were investigated during the pressure oxidation of pyrite in the presence of calcium carbonate. It was found that the shift to an alkaline leaching environment favours the formation of soluble sulphate products over anhydrite (an industrial scale), but that the increase in kinetics is likely due to an increase in pH and carbonate/bicarbonate concentrations. The presence of silica in the autoclave induces the formation of an in situ iron oxyhydroxide silicate coating and a significant reduction in pyrite oxidation, which was minimized by addition of sodium carbonate.

Pressure oxidation of refractory gold ores containing carbonate minerals is conducted under neutral/alkaline conditions in order to promote fast kinetics, reduced reagent consumption and suppressing the formation of elemental sulphur and CO2 (which reduces the effectiveness of the process). In this work, both the addition of sodium carbonate and the presence of silica were investigated during the pressure oxidation of pyrite in the presence of calcium carbonate. It was found that the shift to an alkaline leaching environment favours the formation of soluble sulphate products over anhydrite (an industrial scale), but that the increase in kinetics is likely due to an increase in pH and carbonate/bicarbonate concentrations. The presence of silica in the autoclave induces the formation of an in situ iron oxyhydroxide silicate coating and a significant reduction in pyrite oxidation, which was minimized by addition of sodium carbonate.

A soil profile was taken close to Skellefteå in Västerbotten, northern Sweden. The profile has an upper oxidised zone, 30 cm thick, underlain by a transitions zone, in this paper called accumulation zone, and a reduced zone at 160 cm depth. pH was measured in the field and samples from all zones were analysed for major and trace elements by ICP-SFMS. A batch test was performed on samples from the three zones. Optical microscopy and SEM were used to study mineralogy, focusing on the occurrence of framboidal pyrite. The results were compared with those of profiles in the Luleåarea further north, studied earlier. The results clearly show that the sampled soil profile in the Skellefteå area is of similar types as the soils in the Luleå area. A distinct upper oxidation zone has been developed in all profiles with a strong depletion of S, due to oxidation of iron sulphides when these sediments have been exposed to atmospheric oxygen. This oxidation appears to be stronger in the Luleå profiles than in theSkellefteå profile, possibly because they have oxidised a longer time. All the Luleå profiles and theSkellefteå profiles are acid sulphate soils. There is a depletion of sulphide-associated trace elements such as Cd, Cu, Ni and Zn in the oxidation zone due to the oxidation of iron sulphides with subsequent low pH and leaching. This depletion is more pronounced in the Luleå profiles than in the Skellefteå profile. There is a tendency for secondary accumulation in the accumulation zone, in the Skellefteå profile close to the groundwater table in particular. The batch test in the Skellefteå profile allowed for the observation that the highest concentrations occurred at the groundwater level. Framboidal pyrite occurs in the Skellefteå profile as well as in the Luleå profiles. In the Skellefteåprofile there is a positive correlation between organic matter, shells and framboidal pyrite, illustrating that organic matter was important for the formation of framboidal pyrite. Although most of the pyrite has been oxidized and dissolved in the oxidized zone, there was still some framboidal pyrite left, possibly protected by shells and organic matter.

No description available.

No description available.

Pyrite (FeS2) is commonly present in complex sulphide ores in significant amounts. After the enrichment of such ores by flotation, pyrite is either produced as a separate concentrate and sold to acid manufactures or removed and disposed off as tailing. Due to lack of demand from manufacturers, most of pyrites is usually disposed off as tailing. Therefore, pyrite is usually a waste from complex sulphide ores. Yet, it may be a remediation additive for calcareous soils and calcareous- alkali soils deficient in Fe and other micronutrients such as Cu, Zn and Mn. Waste pyrite may be also an alternative amendment to gypsum because of the production of sulphuric acid which is effectively used in the reclamation of calcareous alkali soils. The effectiveness of adding waste pyrite and sulphuric acid produced from waste pyrite to calcareous-alkali soil (Sarayk&ouml / y-Ankara) and calcareous soil (Gaziantep) was studied under laboratory conditions. Pure gypsum was also used as an amendment for the comparison of the effectiveness of waste pyrite in the reclamation of alkali soils. Gypsum, powder waste pyrite and sulphuric acid were applied to the soil with reference to the gypsum requirement (GR) of the soils. Greenhouse pot tests were carried out with wheat as test plant to determine the effect of waste pyrite treatment on the plant yield (wheat) and on the amount of micronutrient (Fe, Cu, Zn, Mn) essential for plant growth. Hazard potential of pyritic tailings in terms of heavy metal contamination was also taken into account. The results showed that the soil pH and exchangeable sodium percentage (ESP), indicators of alkalization, decreased upon pyrite addition to calcareous- alkali soils of Sarayk&ouml / y-Ankara. It was also found that pyritic tailings were effective in the increasing level of essential micronutrients (Fe, Cu, Zn and Mn) for plant growth in both soils. This was ascertained by the dry matter yield of the plants in the green house pot tests. Heavy metal toxicity caused by pyrite which is a rightful concern remained well below the legal limits in the soils. Thus, it was concluded that the application of pyritic tailings promoted rapid amelioration of calcareous-alkali soil (Sarayk&ouml / y-Ankara) and calcareous soil (Gaziantep) with no deleterious heavy metal contamination.

On retrouve des contaminations d’aquifèr à l’arsenic dans touts les deltaï de l'Asie du Sud-Est, y compris dans le delta du Mékong, ce qui affecte la santé de millions de personnes. L’arsenic est très sensible aux fluctuations des conditions redox qui sont générés par les cycles alternés humides/secs pendant la saison de mousson. Une étude sur les caractéristiques géophysiques et chimiques du sol et des eaux souterraines dans le district de An Phu, dans le haut du delta du Mékong au Vietnam, suggère une forté contamination à l’As dans cette région. Les données chimiques et géophysiques indiquent une forte corrélation entre concentrations dans les eaux souterraines anoxiques et conductivité des sols. La liberation de l’arsenic est associée à la dissolution réductrice induih par des microorganisms des colloïdes et (oxyhydr)oxydes de fer dans des conditions d'oxydo-réduction oscillantes. La présence de bactéries sulforéductrices a le potentiel de stabiliser l’arsenic dans la phase solide et de l’atténuer dans la phase aqueuse par adsorption / désorption de l’arsenic sur les (oxyhydr)oxydes, et / ou sulfures de fer via la formation de complexes thiols. En raison de la teneur en pyrite élevée dans les sédiments, l'oxydation de la pyrite peut abaisser le pH et conduire à l'inhibition de la réduction microbienne du sulfate et aime empêcher la séquestration de l’arsenic dissous. Bien que le cycle biogéochimique de l’arsenic dans un système dynamique d’oxydoréduction soit une problématique complexe, il a été possible de renforcer notre compréhension de ce système / Aquifer arsenic (As) contamination is occuring throughout deltaic areas of Southeast Asia, including the Mekong Delta, and affects the health of millions of people. As is highly sensitive to fluctuations of redox conditions which are generated by the alternating wet-dry cycles during the monsoonal seasons. A survey of geophysical and chemical characteristics of soil and groundwater in the An Phu district, located in the vicinity of the Mekong Delta in Vietnam, shows the occurrence high As aqueous concentration in this region. Chemical and geophysical data indicate a strong positive correlation between As concentrations in the anoxic groundwater and conductivity of soils. In addition, mechanisms of As release are shown to be associated with colloidal and iron (oxyhydr)oxides which undergo microbial mediated reductive dissolution under redox oscilatting conditions. The presence of sulfate microbial reduction potentially stabilizes As in the solid phase and diminish As in the aqueous phase through the adsorption/desorption of As onto iron (oxyhydr)oxides and/ or sulfides with formation of thiols complexes in solid phase. Because of the high pyrite content in sediment, pyrite oxidation may drop in pH values, leads to inhibition of sulfate reducing bacteria and reduces sequestration of dissolved As. Although the biogeochemical cycling of redox sensitive species such as As in dynamic systems is challenging, it has been possible to strengthen our collective understanding of such system.