The Caldes de Boi geothermal waters show important differences in pH (6.5–9.6) and temperature (1... more The Caldes de Boi geothermal waters show important differences in pH (6.5–9.6) and temperature (15.9oC–52oC) despite they have a common origin and a very simple circuit at depth (4km below the recharge area level). Thes differences are the result of secondary processes such as conductive cooling, mixing with colder shallower waters, and input of external CO2, which affect each spring to a different extent in the terminal part of the thermal circuit.In this paper, the secondary processes that control the geochemical evolution of this system have been addressed using a geochemical dataset spanning over 20 years and combining different approaches: classical geochemical calculations and geochemical modelling. Mixing between a cold and a thermal end-member, cooling and CO2 exchange are the processes affecting the spring waters with different intensity over time. These differences in the intensity of the secondary processes could be controlled by the effect of climate and indirectly by th...
Chalcopyrite dissolution kinetics in the pH range of 1 to 3 were studied by means of long-term fl... more Chalcopyrite dissolution kinetics in the pH range of 1 to 3 were studied by means of long-term flow-through experiments to obtain a dissolution rate law which can be coupled with reactive transport models to forecast Acid Rock Drainage. In the range of conditions under study, the rate of chalcopyrite dissolution is only slightly dependent on hydrogen ion activity, increasing with decreasing pH. The steady-state dissolution rates obtained in the present study were combined with earlier results presented by Acero et al. (2007a) to obtain the following expression for chalcopyrite dissolution rate law: where Rchalcopyrite is the chalcopyrite dissolution rate (mol m-2 s-1), aH+ is the activity of hydrogen ion in solution, R is the gas constant (kJ mol-1 K-1) and T is the temperature (K). This expression can applied through a wide range of environmental conditions similar to the ones found in systems affected by acid drainage. In agreement with earlier chalcopyrite kinetic studies, iron w...
espanolEl sistema geotermal de Tiermas representa una de las zonas con mayor potencial geotermico... more espanolEl sistema geotermal de Tiermas representa una de las zonas con mayor potencial geotermico de Aragon y, sin embargo, se sabe todavia poco acerca de sus caracteristicas hidrologicas y geoquimicas. En este trabajo se presentan los principales rasgos hidroquimicos de estas aguas y se determina su temperatura en profundidad mediante la aplicacion de geotermometros quimicos. Estas aguas tienen una afinidad clorurada sulfatada sodica, una temperatura de surgencia de casi 40 °C y un caudal de unos 200 l/s. El acuifero mas probable se localizaria en los carbonatos del Paleoceno y Eoceno, pero debido a la complejidad estructural de la zona, las aguas entrarian en contacto con la facies evaporitica del transito Eoceno–Oligoceno, adquiriendo asi dicha afinidad. Se han distinguido dos grupos hidroquimicos con una diferente salinidad, relacion Na/Cl y concen- traciones de SO4 y TSD. A pesar de las variaciones composicionales detectadas en las surgencias, los calculos geotermometricos real...
The release of arsenic (As) from deltaic sediments into groundwater is an issue that exposes mill... more The release of arsenic (As) from deltaic sediments into groundwater is an issue that exposes millions of people in South-East Asia to toxic levels of As via drinking water. While reductive dissolution of iron oxyhydroxides and the associated As is a known mechanism of release, there are areas in which the sediments do not harbor iron oxyhydroxides. For instance, in the Vietnamese Mekong Delta, in a reduced, As-rich, peat layer harboring a brackish porewater and interpreted as a relic from a mangrove depositional environment [1], As is found associated with arsenian pyrite and natural organic matter (NOM). Flow-through experiments show that this peat layer releases a large amount of As and characterization of the solid phase reveals that both arsenian pyrite and NOM contribute approximately equally to the release. Furthermore, poisoning of the sediment decreased the amount of As released, suggesting a microbially-mediated process. However, the mechanism of As release from arsenian py...
Acid mine drainage (AMD), generated by sulphide oxidative dissolution, leads to high concentratio... more Acid mine drainage (AMD), generated by sulphide oxidative dissolution, leads to high concentrations of dissolved metals and arsenic and it is a major cause of water contamination world-wide. The Iberian Pyrite Belt (IPB) is the major reserve of massive pyrite deposits in the world, with more than one hundred abandoned mines. Oxidation of pyrite and the lack of alkalinity source roks in the region generates a huge amount of AMD, collected by the Tinto and Odiel rivers, which transport an enormous amount of metal(loid)s into the Ria de Huelva and Gulf of Cadiz (eg. 36 tons per year of As, Olías et al., 2006).
In this work, some of the most important irreversible processes (cooling, mixing and CO2 exchange... more In this work, some of the most important irreversible processes (cooling, mixing and CO2 exchange) affecting the hydrogeochemistry of alkaline thermal systems developed in crystalline rocks are studied. The effects of those processes have been quantified with the assistance of geochemical modeling applied to the Panticosa geothermal system (central sector of the Axial Zone of the Spanish Pyrenees). The most important feature of this plutonic complex related to the thermal springs is the intense fracture network which has enhanced the development of the geothermal system, gathering the main water conducting flow-paths. These structural features seem to be involved in the development of this thermal circuit at depth (Fig. 1).
Arsenic contamination in groundwater is pervasive throughout deltaic regions of Southeast Asia an... more Arsenic contamination in groundwater is pervasive throughout deltaic regions of Southeast Asia and threatens the health of millions. The speciation of As in sediments overlying contaminated aquifers is poorly constrained. Here, we investigate the chemical and mineralogical compositions of sediment cores collected from the Mekong Delta in Vietnam, elucidate the speciation of iron and arsenic, and relate them to the sediment depositional environment. Gradual dissolution of ferric (oxyhydr)oxides with depth is observed down to 7 m, corresponding to the establishment of reducing conditions. Within the reduced sediment, layers originating from marine, coastal or alluvial depositional environments are identified and their age is consistent with a late Holocene transgression in the Mekong Delta. In the organic matter- and sulfur-rich layers, arsenic is present in association with organic matter through thiol-bonding and in the form of arsenian pyrite. The highest arsenic concentration (34-...
Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosp... more Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, w...
The Caldes de Boi geothermal waters show important differences in pH (6.5–9.6) and temperature (1... more The Caldes de Boi geothermal waters show important differences in pH (6.5–9.6) and temperature (15.9oC–52oC) despite they have a common origin and a very simple circuit at depth (4km below the recharge area level). Thes differences are the result of secondary processes such as conductive cooling, mixing with colder shallower waters, and input of external CO2, which affect each spring to a different extent in the terminal part of the thermal circuit.In this paper, the secondary processes that control the geochemical evolution of this system have been addressed using a geochemical dataset spanning over 20 years and combining different approaches: classical geochemical calculations and geochemical modelling. Mixing between a cold and a thermal end-member, cooling and CO2 exchange are the processes affecting the spring waters with different intensity over time. These differences in the intensity of the secondary processes could be controlled by the effect of climate and indirectly by th...
Chalcopyrite dissolution kinetics in the pH range of 1 to 3 were studied by means of long-term fl... more Chalcopyrite dissolution kinetics in the pH range of 1 to 3 were studied by means of long-term flow-through experiments to obtain a dissolution rate law which can be coupled with reactive transport models to forecast Acid Rock Drainage. In the range of conditions under study, the rate of chalcopyrite dissolution is only slightly dependent on hydrogen ion activity, increasing with decreasing pH. The steady-state dissolution rates obtained in the present study were combined with earlier results presented by Acero et al. (2007a) to obtain the following expression for chalcopyrite dissolution rate law: where Rchalcopyrite is the chalcopyrite dissolution rate (mol m-2 s-1), aH+ is the activity of hydrogen ion in solution, R is the gas constant (kJ mol-1 K-1) and T is the temperature (K). This expression can applied through a wide range of environmental conditions similar to the ones found in systems affected by acid drainage. In agreement with earlier chalcopyrite kinetic studies, iron w...
espanolEl sistema geotermal de Tiermas representa una de las zonas con mayor potencial geotermico... more espanolEl sistema geotermal de Tiermas representa una de las zonas con mayor potencial geotermico de Aragon y, sin embargo, se sabe todavia poco acerca de sus caracteristicas hidrologicas y geoquimicas. En este trabajo se presentan los principales rasgos hidroquimicos de estas aguas y se determina su temperatura en profundidad mediante la aplicacion de geotermometros quimicos. Estas aguas tienen una afinidad clorurada sulfatada sodica, una temperatura de surgencia de casi 40 °C y un caudal de unos 200 l/s. El acuifero mas probable se localizaria en los carbonatos del Paleoceno y Eoceno, pero debido a la complejidad estructural de la zona, las aguas entrarian en contacto con la facies evaporitica del transito Eoceno–Oligoceno, adquiriendo asi dicha afinidad. Se han distinguido dos grupos hidroquimicos con una diferente salinidad, relacion Na/Cl y concen- traciones de SO4 y TSD. A pesar de las variaciones composicionales detectadas en las surgencias, los calculos geotermometricos real...
The release of arsenic (As) from deltaic sediments into groundwater is an issue that exposes mill... more The release of arsenic (As) from deltaic sediments into groundwater is an issue that exposes millions of people in South-East Asia to toxic levels of As via drinking water. While reductive dissolution of iron oxyhydroxides and the associated As is a known mechanism of release, there are areas in which the sediments do not harbor iron oxyhydroxides. For instance, in the Vietnamese Mekong Delta, in a reduced, As-rich, peat layer harboring a brackish porewater and interpreted as a relic from a mangrove depositional environment [1], As is found associated with arsenian pyrite and natural organic matter (NOM). Flow-through experiments show that this peat layer releases a large amount of As and characterization of the solid phase reveals that both arsenian pyrite and NOM contribute approximately equally to the release. Furthermore, poisoning of the sediment decreased the amount of As released, suggesting a microbially-mediated process. However, the mechanism of As release from arsenian py...
Acid mine drainage (AMD), generated by sulphide oxidative dissolution, leads to high concentratio... more Acid mine drainage (AMD), generated by sulphide oxidative dissolution, leads to high concentrations of dissolved metals and arsenic and it is a major cause of water contamination world-wide. The Iberian Pyrite Belt (IPB) is the major reserve of massive pyrite deposits in the world, with more than one hundred abandoned mines. Oxidation of pyrite and the lack of alkalinity source roks in the region generates a huge amount of AMD, collected by the Tinto and Odiel rivers, which transport an enormous amount of metal(loid)s into the Ria de Huelva and Gulf of Cadiz (eg. 36 tons per year of As, Olías et al., 2006).
In this work, some of the most important irreversible processes (cooling, mixing and CO2 exchange... more In this work, some of the most important irreversible processes (cooling, mixing and CO2 exchange) affecting the hydrogeochemistry of alkaline thermal systems developed in crystalline rocks are studied. The effects of those processes have been quantified with the assistance of geochemical modeling applied to the Panticosa geothermal system (central sector of the Axial Zone of the Spanish Pyrenees). The most important feature of this plutonic complex related to the thermal springs is the intense fracture network which has enhanced the development of the geothermal system, gathering the main water conducting flow-paths. These structural features seem to be involved in the development of this thermal circuit at depth (Fig. 1).
Arsenic contamination in groundwater is pervasive throughout deltaic regions of Southeast Asia an... more Arsenic contamination in groundwater is pervasive throughout deltaic regions of Southeast Asia and threatens the health of millions. The speciation of As in sediments overlying contaminated aquifers is poorly constrained. Here, we investigate the chemical and mineralogical compositions of sediment cores collected from the Mekong Delta in Vietnam, elucidate the speciation of iron and arsenic, and relate them to the sediment depositional environment. Gradual dissolution of ferric (oxyhydr)oxides with depth is observed down to 7 m, corresponding to the establishment of reducing conditions. Within the reduced sediment, layers originating from marine, coastal or alluvial depositional environments are identified and their age is consistent with a late Holocene transgression in the Mekong Delta. In the organic matter- and sulfur-rich layers, arsenic is present in association with organic matter through thiol-bonding and in the form of arsenian pyrite. The highest arsenic concentration (34-...
Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosp... more Sulfate reduction and its associated contaminant immobilization in marsh soils supporting a phosphogypsum stack was examined by pore-water and solid analysis, selective extractions, microscopy and sulfur K-edge X-ray absorption near-edge structure (XANES) spectroscopy. The negative impact of this stack on estuarine environments is a concerning problem. In the weathering profile, total concentrations of most pollutants increase with depth; instead, dissolved contents in pore-waters increase to middle of the saturated zone but then decrease drastically down to reach the marsh due to sulfide precipitation. Excess of acid-volatile sulfide plus pyritic sulfur over metals bound to the oxidizable fraction indicates that sulfide precipitation is the main mechanism responsible for metal removal in the marsh. Thus, abundant pyrite occurred as framboidal grains, in addition to other minor sulfides of As, Zn and Cu as isolated particles. Moreover, high contents of elemental sulfur were found, w...
The Caldes de Boí geothermal waters show important differences in pH (6.5-9.6) and temperature (1... more The Caldes de Boí geothermal waters show important differences in pH (6.5-9.6) and temperature (15.9ºC-52ºC) despite they have a common origin and a very simple circuit at depth (4km below the recharge area level). These differences are the result of secondary processes such as conductive cooling, mixing with colder shallower waters, and input of external CO 2 , which affect each spring to a different extent in the terminal part of the thermal circuit. In this paper, the secondary processes that control the geochemical evolution of this system have been addressed using a geochemical dataset spanning over 20 years and combining different approaches: classical geochemical calculations and geochemical modelling. Mixing between a cold and a thermal end-member, cooling and CO 2 exchange are the processes affecting the spring waters with different intensity over time. These differences in the intensity of the secondary processes could be controlled by the effect of climate and indirectly by the geomorphological and hydrogeological setting of the different springs. Infiltration recharging the shallow aquifer is dominant during the rainy seasons and the extent of the mixing process is greater, at least in some springs. Moreover, significant rainfall can produce a decrease in the ground temperature favouring the conductive cooling. Finally, the geomorphological settings of the springs determine the thickness and the hydraulic properties of the saturated layer below them and, therefore, they affect the extent of the mixing process between the deep thermal waters and the shallower cold waters. The understanding of the compositional changes in the thermal waters and the main factors that could affect them is a key issue to plan the future management of the geothermal resources of the Caldes de Boí system. Here, we propose to use a simple methodology to assess the effect of those factors, which could affect the quality of the thermal waters for balneotherapy at long-term scale. Furthermore, the methodology used in this study can be applied to other geothermal systems.
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