26 research outputs found
Devenir du seÌleÌniate dans les sols : Mise en eÌvidence expeÌrimentale et modeÌlisation des pheÌnomeÌnes d'hysteÌreÌse de sorption/deÌsorption
In the context of future storage of nuclear material in deep geological layers, the transfer of selenium-79 from groundwater to biosphere through irrigation is one of the scenarios considered by the ANDRA (National Agency for Radioactive Waste Management). So, the soil would act as an interface between the geosphere and biosphere. Actually the model adopted to evaluate the element mobility in soil is based on a simple representation of its distribution between the quantity adsorbed on the soil and the amount remaining in the solution (KD model). Such distribution is considered as instantaneous, reversible and linear with the concentration of contamination. This model has some inadequacies with respect to selenium because this latter can be present in different redox states that control its mobility and whose transformation kinetics among states are poorly known (Se(-II), Se(0), Se(IV) and Se(VI)). In order to improve predictions on the mobility of selenium in soil, selenate (Se(VI)) - which is the most mobile form - has been used to study its interactions with respect to two different soils (soil B and soil R). A kinetic model, alternative to the Kd model, has been developed to describe the evolution of stocks of Se(VI) in solution. This model considers that a fraction of selenium is associated with soil in a reversibly way (potentially mobile) and a portion of it is stabilized in soil (pseudo-irreversibly fixed). This model integrates on one hand, in the soil, kinetics of biotic and abiotic stabilization and on the other hand, in solution, a reduction kinetic. With the goal of acquiring the parameters of the models, various experiments using dialysis bags have been effec- tuated, both in batch and with open-flow reactors. The parameter acquisition has allowed kinetic and Kd models to be compared in different realistic scenarios of contamination (chronic or sequential) of a surface soil with 79Se(VI). In addition, the sorption mechanisms of Se(VI) have been evaluated in the two soils in batch adding spe- cific competitors (humic acid and calcium carbonates) that can sorb on solid sites such as selenate. This study has been completed with the analysis of the sorption of Se(VI) on pure phases available on the market (silica, alumi- num hydroxide, goethite, bentonite, calcium carbonate and humic acids) or extracted from a soil (humic sub- stances). This investigation has been carried out at different concentrations of Se(VI) (10-8, 10-6 et/ou 10-3 mol/L). In addition, some pure reactive phases have been added to the soil in order to study the solid-solid interaction having a role on the sorption of Se(VI). This study has underlined that in the R-soil Se(VI) was sorbed in the form of outer sphere complexes (OSC) at con- centrations lower than 10-6 mol/L, whereas in B-soil, the majority were sorbed as inner sphere complexes (ISC). As the formation of OSC is reversible and instantaneous, in experiments with open-flow reactors, the use of Kd model was sufficient to describe the sorption of Se(VI) in R-soil. On the contrary, for soil B, the study has shown that the Kd model, unlike the kinetic model, was inadequate to describe the pseudo-irreversible sorption of Se(VI), caused by the formation of ISC. Due to the supply of nutrients for microorganisms, it has been shown that biotic mecha- nisms predominated in soil B, due to the utilization of cellulose dialysis bags. However, abiotic mechanisms took places in soil B, too. The studies on pure phases have shown that only aluminum hydroxide (pH 5.2 and 8) and goethite (pH 5.2) could sorb Se(VI), respectively in a pseudo-irreversible and reversible way (for [Se(VI)] < 10-6 mol/L). Moreover, it has been shown that, in both soils, the addition of some pure phases (goethite and aluminum hydrox- ide), could cause an increase or a decrease of the sorption of Se(VI) with respect to the one expected (additivity reaction). This study has shown that, knowing only the element composition of the soil, it is not sufficient to evaluate the sorption of selenate without any experimentation.Dans le contexte des futurs stockages des matieÌres nucleÌaires en couches geÌologiques profondes, le transfert de seÌleÌnium 79 des eaux de nappes vers la biospheÌre, par le biais de l'irrigation, est un des scenarii envisageÌs par l'ANDRA. Le sol servirait alors d'interface entre la geÌospheÌre et la biospheÌre. Le modeÌle actuellement utiliseÌ pour eÌvaluer la mobiliteÌ de nombreux eÌleÌments dans le sol repose sur une repreÌ- sentation simple de leur distribution entre la quantiteÌ adsorbeÌe sur le sol et la quantiteÌ restante en solution (mo- deÌle Kd), consideÌreÌe comme instantaneÌe, reÌversible et lineÌaire avec la concentration de contamination. Ce mo- deÌle preÌsente des lacunes vis-aÌ-vis du seÌleÌnium puisque ce dernier peut eÌtre preÌsent sous diffeÌrents eÌtats redox qui controÌlent sa mobiliteÌ et dont les cineÌtiques de transformation entre ces eÌtats sont peu connues (Se(-II), Se(0), Se(IV) et Se(VI)). Dans le but d'ameÌliorer les preÌdictions faites sur la mobiliteÌ du seÌleÌnium dans un sol, le seÌleÌniate (Se(VI)), qui est la forme la plus mobile, a eÌteÌ utiliseÌ pour eÌtudier ses interactions vis-aÌ-vis de deux sols diffeÌrents (sol B et sol R). Un modeÌle cineÌtique, alternatif au modeÌle Kd, a eÌteÌ deÌveloppeÌ pour deÌcrire l'eÌvolution des stocks de Se(VI) en solution, en consideÌrant une fraction de seÌleÌnium associeÌe au sol de façon reÌversible (potentiellement mobile) et une fraction stabiliseÌe sur le sol (fixeÌe pseudo-irreÌversiblement). Ce modeÌle inteÌgre des cineÌtiques de stabilisation biotique et abiotique sur le sol, et une cineÌtique de reÌduction en solution. Afin d'acqueÌrir les parameÌtres des modeÌles, des expeÌriences en batchs et en reÌacteurs aÌ flux ouvert avec l'utilisation de sacs aÌ dialyse ont eÌteÌ reÌaliseÌes. L'acquisition des parameÌtres a permis de confronter les modeÌles cineÌtiques et Kd dans diffeÌrents scenarii reÌalistes de contamination (chronique ou seÌquentielle) d'un sol de surface par du 79Se(VI). De plus, les meÌcanismes de sorption du Se(VI) au sein des deux sols ont eÌteÌ eÌvalueÌs en batch avec l'ajout de com- peÌtiteurs speÌcifiques vis-aÌ-vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de cal- cium). Ceci a eÌteÌ compleÌteÌ avec l'eÌtude de la sorption du Se(VI) sur des phases pures commerciales (silice, hy- droxyde d'aluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites d'un sol (subs- tances humiques), pour diffeÌrentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de l'impact de l'ajout de phases pures reÌactives, dans les sols, sur la sorption du Se(VI). Il a eÌteÌ montreÌ que le Se(VI) eÌtait sorbeÌ sous la forme de complexes de spheÌres externes (CSE) au sein du sol R pour des concentrations infeÌrieures aÌ 10-6 mol/L, tandis que dans le sol B, la majoriteÌ eÌtait sorbeÌe sous la formes de complexes de spheÌre internes (CSI). La formation de CSE eÌtant reÌversible et instantaneÌe, l'utilisation du mo- deÌle Kd eÌtait donc suffisante pour deÌcrire la sorption du Se(VI) au sein du sol R, dans les expeÌriences en reÌacteurs aÌ flux ouvert. A contrario, pour le sol B, il a eÌteÌ montreÌ que le modeÌle Kd, contrairement au modeÌle cineÌtique, preÌsentait des lacunes pour deÌcrire la sorption pseudo-irreÌversible du Se(VI), engendreÌe par la formation de CSI. Il a eÌteÌ montreÌ que les meÌcanismes biotiques eÌtaient majoritaires au sein du sol B, en raison de l'apport de nutri- ments pour les microorganismes, par l'utilisation de sacs aÌ dialyse en cellulose reÌgeÌneÌreÌe. Cependant les meÌca- nismes abiotiques ont aussi eu lieux au sein du sol B. 13/256 Les eÌtudes sur les phases pures ont montreÌ que seuls l'hydroxyde d'aluminium (pH 5,2 et 8) et la goethite (pH 5,2) pouvaient sorber le Se(VI) respectivement de manieÌre pseudo-irreÌversible et reÌversible (pour [Se(VI)] < 10-6 mol/L). Enfin, il a eÌteÌ montreÌ que l'ajout de certaines phases pures (goethite et hydroxyde d'aluminium) au sein des deux sols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport aÌ celle attendue (additiviteÌ reÌactionnelle). Les interactions solide/solide directes et/ou indirectes, (la plus connue eÌtant le coating) peuvent eÌtre aÌ l'origine de la difficulteÌ d'eÌvaluation, de manieÌre geÌneÌrique, de la sorption du Se(VI) au sein du sol, connaissant seulement sa composition eÌleÌmentaire
Devenir du séléniate dans les sols : mise en évidence expérimentale et modélisation des phénomÚnes d'hystérÚse de sorption/désorption
In the context of future storage of nuclear material in deep geological layers, the transfer of selenium-79 from groundwater to biosphere through irrigation is one of the scenarios considered by the ANDRA (National Agency for Radioactive Waste Management). So, the soil would act as an interface between the geosphere and biosphere. Actually the model adopted to evaluate the element mobility in soil is based on a simple representation of its distribution between the quantity adsorbed on the soil and the amount remaining in the solution (KD model). Such distribution is considered as instantaneous, reversible and linear with the concentration of contamination. This model has some inadequacies with respect to selenium because this latter can be present in different redox states that control its mobility and whose transformation kinetics among states are poorly known (Se(-II), Se(0), Se(IV)and Se(VI)). In order to improve predictions on the mobility of selenium in soil, selenate (Se(VI)) - which is the most mobile form - has been used to study its interactions with respect to two different soils (soil B and soil R). Akinetic model, alternative to the Kd model, has been developed to describe the evolution of stocks of Se(VI) in solution. This model considers that a fraction of selenium is associated with soil in a reversibly way (potentially mobile) and a portion of it is stabilized in soil (pseudo-irreversibly fixed). This model integrates on one hand, in the soil, kinetics of biotic and abiotic stabilization and on the other hand, in solution, a reduction kinetic. With the goal of acquiring the parameters of the models, various experiments using dialysis bags have been effectuated, both in batch and with open-flow reactors. The parameter acquisition has allowed kinetic and Kd models to be compared in different realistic scenarios of contamination (chronic or sequential) of a surface soil with 79Se(VI). In addition, the sorption mechanisms of Se(VI) have been evaluated in the two soils in batch adding specific competitors (humic acid and calcium carbonates) that can sorb on solid sites such as selenate. This study has been completed with the analysis of the sorption of Se(VI) on pure phases available on the market (silica, aluminum hydroxide, goethite, bentonite, calcium carbonate and humic acids) or extracted from a soil (humic substances).This investigation has been carried out at different concentrations of Se(VI) (10-8, 10-6 et/ou 10-3 mol/L). In addition, some pure reactive phases have been added to the soil in order to study the solid-solid interaction having a role on the sorption of Se(VI).This study has underlined that in the R-soil Se(VI) was sorbed in the form of outer sphere complexes (OSC) at concentration slower than 10-6 mol/L, whereas in B-soil, the majority were sorbed as inner sphere complexes (ISC). As the formation of OSC is reversible and instantaneous, in experiments with open-flow reactors, the use of Kd model was sufficient to describe the sorption of Se(VI) in R-soil. On the contrary, for soil B, the study has shown that the Kd model, unlike the kinetic model, was inadequate to describe the pseudo-irreversible sorption of Se(VI), caused by the formation of ISC. Due to the supply of nutrients for microorganisms, it has been shown that biotic mechanisms predominated in soil B, due to the utilization of cellulose dialysis bags. However, abiotic mechanisms took places in soil B, too. The studies on pure phases have shown that only aluminum hydroxide (pH 5.2 and 8) and goethite (pH 5.2) could sorb Se(VI), respectively in a pseudo-irreversible and reversible way (for [Se(VI)] < 10-6 mol/L).Moreover, it has been shown that, in both soils, the addition of some pure phases (goethite and aluminum hydroxide),could cause an increase or a decrease of the sorption of Se(VI) with respect to the one expected (additivity reaction).Dans le contexte des futurs stockages des matiĂšres nuclĂ©aires en couches gĂ©ologiques profondes, le transfert de sĂ©lĂ©nium 79 des eaux de nappes vers la biosphĂšre, par le biais de lâirrigation, est un des scenarii envisagĂ©s par lâANDRA. Le sol servirait alors dâinterface entre la gĂ©osphĂšre et la biosphĂšre. Le modĂšle actuellement utilisĂ© pour Ă©valuer la mobilitĂ© de nombreux Ă©lĂ©ments dans le sol repose sur une reprĂ©sentation simple de leur distribution entre la quantitĂ© adsorbĂ©e sur le sol et la quantitĂ© restante en solution (modĂšle Kd), considĂ©rĂ©e comme instantanĂ©e, rĂ©versible et linĂ©aire avec la concentration de contamination. Ce modĂšle prĂ©sente des lacunes vis-Ă -vis du sĂ©lĂ©nium puisque ce dernier peut ĂȘtre prĂ©sent sous diffĂ©rents Ă©tats redox qui contrĂŽlent sa mobilitĂ© et dont les cinĂ©tiques de transformation entre ces Ă©tats sont peu connues (Se(-II), Se(0),Se(IV) et Se(VI)).Dans le but dâamĂ©liorer les prĂ©dictions faites sur la mobilitĂ© du sĂ©lĂ©nium dans un sol, le sĂ©lĂ©niate (Se(VI)), qui est la forme la plus mobile, a Ă©tĂ© utilisĂ© pour Ă©tudier ses interactions vis-Ă -vis de deux sols diffĂ©rents (sol B et sol R).Un modĂšle cinĂ©tique, alternatif au modĂšle Kd, a Ă©tĂ© dĂ©veloppĂ© pour dĂ©crire lâĂ©volution des stocks de Se(VI) en solution, en considĂ©rant une fraction de sĂ©lĂ©nium associĂ©e au sol de façon rĂ©versible (potentiellement mobile) et une fraction stabilisĂ©e sur le sol (fixĂ©e pseudo-irrĂ©versiblement). Ce modĂšle intĂšgre des cinĂ©tiques de stabilisation biotique et abiotique sur le sol, et une cinĂ©tique de rĂ©duction en solution. Afin dâacquĂ©rir les paramĂštres des modĂšles, des expĂ©riences en batchs et en rĂ©acteurs Ă flux ouvert avec lâutilisation de sacs Ă dialyse ont Ă©tĂ© rĂ©alisĂ©es. Lâacquisition des paramĂštres a permis de confronter les modĂšles cinĂ©tiques et Kd dans diffĂ©rents scenarii rĂ©alistes de contamination (chronique ou sĂ©quentielle) dâun sol de surface par du 79Se(VI).De plus, les mĂ©canismes de sorption du Se(VI) au sein des deux sols ont Ă©tĂ© Ă©valuĂ©s en batch avec lâajout de compĂ©titeurs spĂ©cifiques vis-Ă -vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de calcium). Ceci a Ă©tĂ© complĂ©tĂ© avec lâĂ©tude de la sorption du Se(VI) sur des phases pures commerciales (silice, hydroxyde dâaluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites dâun sol (substances humiques), pour diffĂ©rentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de lâimpact de lâajout de phases pures rĂ©actives, dans les sols, sur la sorption du Se(VI).Il a Ă©tĂ© montrĂ© que le Se(VI) Ă©tait sorbĂ© sous la forme de complexes de sphĂšres externes (CSE) au sein du sol R pour des concentrations infĂ©rieures Ă 10-6 mol/L, tandis que dans le sol B, la majoritĂ© Ă©tait sorbĂ©e sous la forme de complexes de sphĂšre internes (CSI). La formation de CSE Ă©tant rĂ©versible et instantanĂ©e, lâutilisation du modĂšle Kd Ă©tait donc suffisante pour dĂ©crire la sorption du Se(VI) au sein du sol R, dans les expĂ©riences en rĂ©acteurs Ă flux ouvert. A contrario, pour le sol B, il a Ă©tĂ© montrĂ© que le modĂšle Kd, contrairement au modĂšle cinĂ©tique, prĂ©sentait des lacunes pour dĂ©crire la sorption pseudo-irrĂ©versible du Se(VI), engendrĂ©e par la formation de CSI. Il a Ă©tĂ© montrĂ© que les mĂ©canismes biotiques Ă©taient majoritaires au sein du sol B, en raison de lâapport de nutriments pour les microorganismes, par lâutilisation de sacs Ă dialyse en cellulose rĂ©gĂ©nĂ©rĂ©e. Cependant les mĂ©canismes abiotiques ont aussi eu lieux au sein du sol B.14/256. Les Ă©tudes sur les phases pures ont montrĂ© que seuls lâhydroxyde dâaluminium (pH 5,2 et 8) et la goethite (pH 5,2) pouvaient sorber le Se(VI) respectivement de maniĂšre pseudo-irrĂ©versible et rĂ©versible (pour [Se(VI)] < 10-6mol/L). Enfin, il a Ă©tĂ© montrĂ© que lâajout de certaines phases pures (goethite et hydroxyde dâaluminium) au sein des deux sols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport Ă celle attendue (additivitĂ© rĂ©actionnelle)
Behaviour of selenate in soils : experimental approch and modelisation of hysteresis of sorption/desorption
Dans le contexte des futurs stockages des matiĂšres nuclĂ©aires en couches gĂ©ologiques profondes, le transfert de sĂ©lĂ©nium 79 des eaux de nappes vers la biosphĂšre, par le biais de lâirrigation, est un des scenarii envisagĂ©s par lâANDRA. Le sol servirait alors dâinterface entre la gĂ©osphĂšre et la biosphĂšre. Le modĂšle actuellement utilisĂ© pour Ă©valuer la mobilitĂ© de nombreux Ă©lĂ©ments dans le sol repose sur une reprĂ©sentation simple de leur distribution entre la quantitĂ© adsorbĂ©e sur le sol et la quantitĂ© restante en solution (modĂšle Kd), considĂ©rĂ©e comme instantanĂ©e, rĂ©versible et linĂ©aire avec la concentration de contamination. Ce modĂšle prĂ©sente des lacunes vis-Ă -vis du sĂ©lĂ©nium puisque ce dernier peut ĂȘtre prĂ©sent sous diffĂ©rents Ă©tats redox qui contrĂŽlent sa mobilitĂ© et dont les cinĂ©tiques de transformation entre ces Ă©tats sont peu connues (Se(-II), Se(0),Se(IV) et Se(VI)).Dans le but dâamĂ©liorer les prĂ©dictions faites sur la mobilitĂ© du sĂ©lĂ©nium dans un sol, le sĂ©lĂ©niate (Se(VI)), qui est la forme la plus mobile, a Ă©tĂ© utilisĂ© pour Ă©tudier ses interactions vis-Ă -vis de deux sols diffĂ©rents (sol B et sol R).Un modĂšle cinĂ©tique, alternatif au modĂšle Kd, a Ă©tĂ© dĂ©veloppĂ© pour dĂ©crire lâĂ©volution des stocks de Se(VI) en solution, en considĂ©rant une fraction de sĂ©lĂ©nium associĂ©e au sol de façon rĂ©versible (potentiellement mobile) et une fraction stabilisĂ©e sur le sol (fixĂ©e pseudo-irrĂ©versiblement). Ce modĂšle intĂšgre des cinĂ©tiques de stabilisation biotique et abiotique sur le sol, et une cinĂ©tique de rĂ©duction en solution. Afin dâacquĂ©rir les paramĂštres des modĂšles, des expĂ©riences en batchs et en rĂ©acteurs Ă flux ouvert avec lâutilisation de sacs Ă dialyse ont Ă©tĂ© rĂ©alisĂ©es. Lâacquisition des paramĂštres a permis de confronter les modĂšles cinĂ©tiques et Kd dans diffĂ©rents scenarii rĂ©alistes de contamination (chronique ou sĂ©quentielle) dâun sol de surface par du 79Se(VI).De plus, les mĂ©canismes de sorption du Se(VI) au sein des deux sols ont Ă©tĂ© Ă©valuĂ©s en batch avec lâajout de compĂ©titeurs spĂ©cifiques vis-Ă -vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de calcium). Ceci a Ă©tĂ© complĂ©tĂ© avec lâĂ©tude de la sorption du Se(VI) sur des phases pures commerciales (silice, hydroxyde dâaluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites dâun sol (substances humiques), pour diffĂ©rentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de lâimpact de lâajout de phases pures rĂ©actives, dans les sols, sur la sorption du Se(VI).Il a Ă©tĂ© montrĂ© que le Se(VI) Ă©tait sorbĂ© sous la forme de complexes de sphĂšres externes (CSE) au sein du sol R pour des concentrations infĂ©rieures Ă 10-6 mol/L, tandis que dans le sol B, la majoritĂ© Ă©tait sorbĂ©e sous la forme de complexes de sphĂšre internes (CSI). La formation de CSE Ă©tant rĂ©versible et instantanĂ©e, lâutilisation du modĂšle Kd Ă©tait donc suffisante pour dĂ©crire la sorption du Se(VI) au sein du sol R, dans les expĂ©riences en rĂ©acteurs Ă flux ouvert. A contrario, pour le sol B, il a Ă©tĂ© montrĂ© que le modĂšle Kd, contrairement au modĂšle cinĂ©tique, prĂ©sentait des lacunes pour dĂ©crire la sorption pseudo-irrĂ©versible du Se(VI), engendrĂ©e par la formation de CSI. Il a Ă©tĂ© montrĂ© que les mĂ©canismes biotiques Ă©taient majoritaires au sein du sol B, en raison de lâapport de nutriments pour les microorganismes, par lâutilisation de sacs Ă dialyse en cellulose rĂ©gĂ©nĂ©rĂ©e. Cependant les mĂ©canismes abiotiques ont aussi eu lieux au sein du sol B.14/256. Les Ă©tudes sur les phases pures ont montrĂ© que seuls lâhydroxyde dâaluminium (pH 5,2 et 8) et la goethite (pH 5,2) pouvaient sorber le Se(VI) respectivement de maniĂšre pseudo-irrĂ©versible et rĂ©versible (pour [Se(VI)] < 10-6mol/L). Enfin, il a Ă©tĂ© montrĂ© que lâajout de certaines phases pures (goethite et hydroxyde dâaluminium) au sein des deux sols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport Ă celle attendue (additivitĂ© rĂ©actionnelle).In the context of future storage of nuclear material in deep geological layers, the transfer of selenium-79 from groundwater to biosphere through irrigation is one of the scenarios considered by the ANDRA (National Agency for Radioactive Waste Management). So, the soil would act as an interface between the geosphere and biosphere. Actually the model adopted to evaluate the element mobility in soil is based on a simple representation of its distribution between the quantity adsorbed on the soil and the amount remaining in the solution (KD model). Such distribution is considered as instantaneous, reversible and linear with the concentration of contamination. This model has some inadequacies with respect to selenium because this latter can be present in different redox states that control its mobility and whose transformation kinetics among states are poorly known (Se(-II), Se(0), Se(IV)and Se(VI)). In order to improve predictions on the mobility of selenium in soil, selenate (Se(VI)) - which is the most mobile form - has been used to study its interactions with respect to two different soils (soil B and soil R). Akinetic model, alternative to the Kd model, has been developed to describe the evolution of stocks of Se(VI) in solution. This model considers that a fraction of selenium is associated with soil in a reversibly way (potentially mobile) and a portion of it is stabilized in soil (pseudo-irreversibly fixed). This model integrates on one hand, in the soil, kinetics of biotic and abiotic stabilization and on the other hand, in solution, a reduction kinetic. With the goal of acquiring the parameters of the models, various experiments using dialysis bags have been effectuated, both in batch and with open-flow reactors. The parameter acquisition has allowed kinetic and Kd models to be compared in different realistic scenarios of contamination (chronic or sequential) of a surface soil with 79Se(VI). In addition, the sorption mechanisms of Se(VI) have been evaluated in the two soils in batch adding specific competitors (humic acid and calcium carbonates) that can sorb on solid sites such as selenate. This study has been completed with the analysis of the sorption of Se(VI) on pure phases available on the market (silica, aluminum hydroxide, goethite, bentonite, calcium carbonate and humic acids) or extracted from a soil (humic substances).This investigation has been carried out at different concentrations of Se(VI) (10-8, 10-6 et/ou 10-3 mol/L). In addition, some pure reactive phases have been added to the soil in order to study the solid-solid interaction having a role on the sorption of Se(VI).This study has underlined that in the R-soil Se(VI) was sorbed in the form of outer sphere complexes (OSC) at concentration slower than 10-6 mol/L, whereas in B-soil, the majority were sorbed as inner sphere complexes (ISC). As the formation of OSC is reversible and instantaneous, in experiments with open-flow reactors, the use of Kd model was sufficient to describe the sorption of Se(VI) in R-soil. On the contrary, for soil B, the study has shown that the Kd model, unlike the kinetic model, was inadequate to describe the pseudo-irreversible sorption of Se(VI), caused by the formation of ISC. Due to the supply of nutrients for microorganisms, it has been shown that biotic mechanisms predominated in soil B, due to the utilization of cellulose dialysis bags. However, abiotic mechanisms took places in soil B, too. The studies on pure phases have shown that only aluminum hydroxide (pH 5.2 and 8) and goethite (pH 5.2) could sorb Se(VI), respectively in a pseudo-irreversible and reversible way (for [Se(VI)] < 10-6 mol/L).Moreover, it has been shown that, in both soils, the addition of some pure phases (goethite and aluminum hydroxide),could cause an increase or a decrease of the sorption of Se(VI) with respect to the one expected (additivity reaction)
Devenir du séléniate dans les sols : mise en évidence expérimentale et modélisation des phénomÚnes d'hystérÚse de sorption/désorption
In the context of future storage of nuclear material in deep geological layers, the transfer of selenium-79 from groundwater to biosphere through irrigation is one of the scenarios considered by the ANDRA (National Agency for Radioactive Waste Management). So, the soil would act as an interface between the geosphere and biosphere. Actually the model adopted to evaluate the element mobility in soil is based on a simple representation of its distribution between the quantity adsorbed on the soil and the amount remaining in the solution (KD model). Such distribution is considered as instantaneous, reversible and linear with the concentration of contamination. This model has some inadequacies with respect to selenium because this latter can be present in different redox states that control its mobility and whose transformation kinetics among states are poorly known (Se(-II), Se(0), Se(IV)and Se(VI)). In order to improve predictions on the mobility of selenium in soil, selenate (Se(VI)) - which is the most mobile form - has been used to study its interactions with respect to two different soils (soil B and soil R). Akinetic model, alternative to the Kd model, has been developed to describe the evolution of stocks of Se(VI) in solution. This model considers that a fraction of selenium is associated with soil in a reversibly way (potentially mobile) and a portion of it is stabilized in soil (pseudo-irreversibly fixed). This model integrates on one hand, in the soil, kinetics of biotic and abiotic stabilization and on the other hand, in solution, a reduction kinetic. With the goal of acquiring the parameters of the models, various experiments using dialysis bags have been effectuated, both in batch and with open-flow reactors. The parameter acquisition has allowed kinetic and Kd models to be compared in different realistic scenarios of contamination (chronic or sequential) of a surface soil with 79Se(VI). In addition, the sorption mechanisms of Se(VI) have been evaluated in the two soils in batch adding specific competitors (humic acid and calcium carbonates) that can sorb on solid sites such as selenate. This study has been completed with the analysis of the sorption of Se(VI) on pure phases available on the market (silica, aluminum hydroxide, goethite, bentonite, calcium carbonate and humic acids) or extracted from a soil (humic substances).This investigation has been carried out at different concentrations of Se(VI) (10-8, 10-6 et/ou 10-3 mol/L). In addition, some pure reactive phases have been added to the soil in order to study the solid-solid interaction having a role on the sorption of Se(VI).This study has underlined that in the R-soil Se(VI) was sorbed in the form of outer sphere complexes (OSC) at concentration slower than 10-6 mol/L, whereas in B-soil, the majority were sorbed as inner sphere complexes (ISC). As the formation of OSC is reversible and instantaneous, in experiments with open-flow reactors, the use of Kd model was sufficient to describe the sorption of Se(VI) in R-soil. On the contrary, for soil B, the study has shown that the Kd model, unlike the kinetic model, was inadequate to describe the pseudo-irreversible sorption of Se(VI), caused by the formation of ISC. Due to the supply of nutrients for microorganisms, it has been shown that biotic mechanisms predominated in soil B, due to the utilization of cellulose dialysis bags. However, abiotic mechanisms took places in soil B, too. The studies on pure phases have shown that only aluminum hydroxide (pH 5.2 and 8) and goethite (pH 5.2) could sorb Se(VI), respectively in a pseudo-irreversible and reversible way (for [Se(VI)] < 10-6 mol/L).Moreover, it has been shown that, in both soils, the addition of some pure phases (goethite and aluminum hydroxide),could cause an increase or a decrease of the sorption of Se(VI) with respect to the one expected (additivity reaction).Dans le contexte des futurs stockages des matiĂšres nuclĂ©aires en couches gĂ©ologiques profondes, le transfert de sĂ©lĂ©nium 79 des eaux de nappes vers la biosphĂšre, par le biais de lâirrigation, est un des scenarii envisagĂ©s par lâANDRA. Le sol servirait alors dâinterface entre la gĂ©osphĂšre et la biosphĂšre. Le modĂšle actuellement utilisĂ© pour Ă©valuer la mobilitĂ© de nombreux Ă©lĂ©ments dans le sol repose sur une reprĂ©sentation simple de leur distribution entre la quantitĂ© adsorbĂ©e sur le sol et la quantitĂ© restante en solution (modĂšle Kd), considĂ©rĂ©e comme instantanĂ©e, rĂ©versible et linĂ©aire avec la concentration de contamination. Ce modĂšle prĂ©sente des lacunes vis-Ă -vis du sĂ©lĂ©nium puisque ce dernier peut ĂȘtre prĂ©sent sous diffĂ©rents Ă©tats redox qui contrĂŽlent sa mobilitĂ© et dont les cinĂ©tiques de transformation entre ces Ă©tats sont peu connues (Se(-II), Se(0),Se(IV) et Se(VI)).Dans le but dâamĂ©liorer les prĂ©dictions faites sur la mobilitĂ© du sĂ©lĂ©nium dans un sol, le sĂ©lĂ©niate (Se(VI)), qui est la forme la plus mobile, a Ă©tĂ© utilisĂ© pour Ă©tudier ses interactions vis-Ă -vis de deux sols diffĂ©rents (sol B et sol R).Un modĂšle cinĂ©tique, alternatif au modĂšle Kd, a Ă©tĂ© dĂ©veloppĂ© pour dĂ©crire lâĂ©volution des stocks de Se(VI) en solution, en considĂ©rant une fraction de sĂ©lĂ©nium associĂ©e au sol de façon rĂ©versible (potentiellement mobile) et une fraction stabilisĂ©e sur le sol (fixĂ©e pseudo-irrĂ©versiblement). Ce modĂšle intĂšgre des cinĂ©tiques de stabilisation biotique et abiotique sur le sol, et une cinĂ©tique de rĂ©duction en solution. Afin dâacquĂ©rir les paramĂštres des modĂšles, des expĂ©riences en batchs et en rĂ©acteurs Ă flux ouvert avec lâutilisation de sacs Ă dialyse ont Ă©tĂ© rĂ©alisĂ©es. Lâacquisition des paramĂštres a permis de confronter les modĂšles cinĂ©tiques et Kd dans diffĂ©rents scenarii rĂ©alistes de contamination (chronique ou sĂ©quentielle) dâun sol de surface par du 79Se(VI).De plus, les mĂ©canismes de sorption du Se(VI) au sein des deux sols ont Ă©tĂ© Ă©valuĂ©s en batch avec lâajout de compĂ©titeurs spĂ©cifiques vis-Ă -vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de calcium). Ceci a Ă©tĂ© complĂ©tĂ© avec lâĂ©tude de la sorption du Se(VI) sur des phases pures commerciales (silice, hydroxyde dâaluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites dâun sol (substances humiques), pour diffĂ©rentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de lâimpact de lâajout de phases pures rĂ©actives, dans les sols, sur la sorption du Se(VI).Il a Ă©tĂ© montrĂ© que le Se(VI) Ă©tait sorbĂ© sous la forme de complexes de sphĂšres externes (CSE) au sein du sol R pour des concentrations infĂ©rieures Ă 10-6 mol/L, tandis que dans le sol B, la majoritĂ© Ă©tait sorbĂ©e sous la forme de complexes de sphĂšre internes (CSI). La formation de CSE Ă©tant rĂ©versible et instantanĂ©e, lâutilisation du modĂšle Kd Ă©tait donc suffisante pour dĂ©crire la sorption du Se(VI) au sein du sol R, dans les expĂ©riences en rĂ©acteurs Ă flux ouvert. A contrario, pour le sol B, il a Ă©tĂ© montrĂ© que le modĂšle Kd, contrairement au modĂšle cinĂ©tique, prĂ©sentait des lacunes pour dĂ©crire la sorption pseudo-irrĂ©versible du Se(VI), engendrĂ©e par la formation de CSI. Il a Ă©tĂ© montrĂ© que les mĂ©canismes biotiques Ă©taient majoritaires au sein du sol B, en raison de lâapport de nutriments pour les microorganismes, par lâutilisation de sacs Ă dialyse en cellulose rĂ©gĂ©nĂ©rĂ©e. Cependant les mĂ©canismes abiotiques ont aussi eu lieux au sein du sol B.14/256. Les Ă©tudes sur les phases pures ont montrĂ© que seuls lâhydroxyde dâaluminium (pH 5,2 et 8) et la goethite (pH 5,2) pouvaient sorber le Se(VI) respectivement de maniĂšre pseudo-irrĂ©versible et rĂ©versible (pour [Se(VI)] < 10-6mol/L). Enfin, il a Ă©tĂ© montrĂ© que lâajout de certaines phases pures (goethite et hydroxyde dâaluminium) au sein des deux sols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport Ă celle attendue (additivitĂ© rĂ©actionnelle)
Devenir du séléniate dans les sols (mise en évidence expérimentale et modélisation des phénomÚnes d'hystérÚse de sorption/désorption)
Dans le contexte des futurs stockages des matiĂšres nuclĂ©aires en couches gĂ©ologiques profondes, le transfert desĂ©lĂ©nium 79 des eaux de nappes vers la biosphĂšre, par le biais de l irrigation, est un des scenarii envisagĂ©s parl ANDRA. Le sol servirait alors d interface entre la gĂ©osphĂšre et la biosphĂšre.Le modĂšle actuellement utilisĂ© pour Ă©valuer la mobilitĂ© de nombreux Ă©lĂ©ments dans le sol repose sur une reprĂ©sentationsimple de leur distribution entre la quantitĂ© adsorbĂ©e sur le sol et la quantitĂ© restante en solution (modĂšleKd), considĂ©rĂ©e comme instantanĂ©e, rĂ©versible et linĂ©aire avec la concentration de contamination. Ce modĂšleprĂ©sente des lacunes vis-Ă -vis du sĂ©lĂ©nium puisque ce dernier peut ĂȘtre prĂ©sent sous diffĂ©rents Ă©tats redoxqui contrĂŽlent sa mobilitĂ© et dont les cinĂ©tiques de transformation entre ces Ă©tats sont peu connues (Se(-II), Se(0),Se(IV) et Se(VI)).Dans le but d amĂ©liorer les prĂ©dictions faites sur la mobilitĂ© du sĂ©lĂ©nium dans un sol, le sĂ©lĂ©niate (Se(VI)), qui estla forme la plus mobile, a Ă©tĂ© utilisĂ© pour Ă©tudier ses interactions vis-Ă -vis de deux sols diffĂ©rents (sol B et sol R).Un modĂšle cinĂ©tique, alternatif au modĂšle Kd, a Ă©tĂ© dĂ©veloppĂ© pour dĂ©crire l Ă©volution des stocks de Se(VI) ensolution, en considĂ©rant une fraction de sĂ©lĂ©nium associĂ©e au sol de façon rĂ©versible (potentiellement mobile) etune fraction stabilisĂ©e sur le sol (fixĂ©e pseudo-irrĂ©versiblement). Ce modĂšle intĂšgre des cinĂ©tiques de stabilisationbiotique et abiotique sur le sol, et une cinĂ©tique de rĂ©duction en solution.Afin d acquĂ©rir les paramĂštres des modĂšles, des expĂ©riences en batchs et en rĂ©acteurs Ă flux ouvert avecl utilisation de sacs Ă dialyse ont Ă©tĂ© rĂ©alisĂ©es. L acquisition des paramĂštres a permis de confronter les modĂšlescinĂ©tiques et Kd dans diffĂ©rents scenarii rĂ©alistes de contamination (chronique ou sĂ©quentielle) d un sol de surfacepar du 79Se(VI).De plus, les mĂ©canismes de sorption du Se(VI) au sein des deux sols ont Ă©tĂ© Ă©valuĂ©s en batch avec l ajout de compĂ©titeursspĂ©cifiques vis-Ă -vis de certains sites pouvant sorber ce dernier (acides humiques et carbonates de calcium).Ceci a Ă©tĂ© complĂ©tĂ© avec l Ă©tude de la sorption du Se(VI) sur des phases pures commerciales (silice, hydroxyded aluminium, goethite, bentonite, carbonate de calcium et acides humiques) ou extraites d un sol (substanceshumiques), pour diffĂ©rentes concentrations en Se(VI) (10-8, 10-6 et/ou 10-3 mol/L), de l impact de l ajout dephases pures rĂ©actives, dans les sols, sur la sorption du Se(VI).Il a Ă©tĂ© montrĂ© que le Se(VI) Ă©tait sorbĂ© sous la forme de complexes de sphĂšres externes (CSE) au sein du sol Rpour des concentrations infĂ©rieures Ă 10-6 mol/L, tandis que dans le sol B, la majoritĂ© Ă©tait sorbĂ©e sous la formesde complexes de sphĂšre internes (CSI). La formation de CSE Ă©tant rĂ©versible et instantanĂ©e, l utilisation du modĂšleKd Ă©tait donc suffisante pour dĂ©crire la sorption du Se(VI) au sein du sol R, dans les expĂ©riences en rĂ©acteursĂ flux ouvert.A contrario, pour le sol B, il a Ă©tĂ© montrĂ© que le modĂšle Kd, contrairement au modĂšle cinĂ©tique, prĂ©sentait deslacunes pour dĂ©crire la sorption pseudo-irrĂ©versible du Se(VI), engendrĂ©e par la formation de CSI.Il a Ă©tĂ© montrĂ© que les mĂ©canismes biotiques Ă©taient majoritaires au sein du sol B, en raison de l apport de nutrimentspour les microorganismes, par l utilisation de sacs Ă dialyse en cellulose rĂ©gĂ©nĂ©rĂ©e. Cependant les mĂ©canismesabiotiques ont aussi eu lieux au sein du sol B.14/256Les Ă©tudes sur les phases pures ont montrĂ© que seuls l hydroxyde d aluminium (pH 5,2 et 8) et la goethite (pH 5,2)pouvaient sorber le Se(VI) respectivement de maniĂšre pseudo-irrĂ©versible et rĂ©versible (pour [Se(VI)] < 10-6mol/L).Enfin, il a Ă©tĂ© montrĂ© que l ajout de certaines phases pures (goethite et hydroxyde d aluminium) au sein des deuxsols, pouvait entrainer une augmentation ou une diminution de la sorption du Se(VI) par rapport Ă celle attendue(additivitĂ© rĂ©actionnelle). Les interactions solide/solide directes et/ou indirectes, (la plus connue Ă©tant le coating)peuvent ĂȘtre Ă l origine de la difficultĂ© d Ă©valuation, de maniĂšre gĂ©nĂ©rique, de la sorption du Se(VI) au sein dusol, connaissant seulement sa composition Ă©lĂ©mentaire.In the context of future storage of nuclear material in deep geological layers, the transfer of selenium-79 fromgroundwater to biosphere through irrigation is one of the scenarios considered by the ANDRA (National Agency forRadioactive Waste Management). So, the soil would act as an interface between the geosphere and biosphere.Actually the model adopted to evaluate the element mobility in soil is based on a simple representation of itsdistribution between the quantity adsorbed on the soil and the amount remaining in the solution (KD model). Suchdistribution is considered as instantaneous, reversible and linear with the concentration of contamination. Thismodel has some inadequacies with respect to selenium because this latter can be present in different redox statesthat control its mobility and whose transformation kinetics among states are poorly known (Se(-II), Se(0), Se(IV)and Se(VI)). In order to improve predictions on the mobility of selenium in soil, selenate (Se(VI)) - which is themost mobile form - has been used to study its interactions with respect to two different soils (soil B and soil R). Akinetic model, alternative to the Kd model, has been developed to describe the evolution of stocks of Se(VI) insolution. This model considers that a fraction of selenium is associated with soil in a reversibly way (potentiallymobile) and a portion of it is stabilized in soil (pseudo-irreversibly fixed). This model integrates on one hand, inthe soil, kinetics of biotic and abiotic stabilization and on the other hand, in solution, a reduction kinetic.With the goal of acquiring the parameters of the models, various experiments using dialysis bags have been effectuated,both in batch and with open-flow reactors. The parameter acquisition has allowed kinetic and Kd modelsto be compared in different realistic scenarios of contamination (chronic or sequential) of a surface soil with79Se(VI). In addition, the sorption mechanisms of Se(VI) have been evaluated in the two soils in batch adding specificcompetitors (humic acid and calcium carbonates) that can sorb on solid sites such as selenate. This study hasbeen completed with the analysis of the sorption of Se(VI) on pure phases available on the market (silica, aluminumhydroxide, goethite, bentonite, calcium carbonate and humic acids) or extracted from a soil (humic substances).This investigation has been carried out at different concentrations of Se(VI) (10-8, 10-6 et/ou 10-3 mol/L). Inaddition, some pure reactive phases have been added to the soil in order to study the solid-solid interaction havinga role on the sorption of Se(VI).This study has underlined that in the R-soil Se(VI) was sorbed in the form of outer sphere complexes (OSC) at concentrationslower than 10-6 mol/L, whereas in B-soil, the majority were sorbed as inner sphere complexes (ISC). Asthe formation of OSC is reversible and instantaneous, in experiments with open-flow reactors, the use of Kd modelwas sufficient to describe the sorption of Se(VI) in R-soil. On the contrary, for soil B, the study has shown that theKd model, unlike the kinetic model, was inadequate to describe the pseudo-irreversible sorption of Se(VI), causedby the formation of ISC. Due to the supply of nutrients for microorganisms, it has been shown that biotic mechanismspredominated in soil B, due to the utilization of cellulose dialysis bags. However, abiotic mechanisms tookplaces in soil B, too.The studies on pure phases have shown that only aluminum hydroxide (pH 5.2 and 8) and goethite (pH 5.2) couldsorb Se(VI), respectively in a pseudo-irreversible and reversible way (for [Se(VI)] < 10-6 mol/L).Moreover, it has been shown that, in both soils, the addition of some pure phases (goethite and aluminum hydroxide),could cause an increase or a decrease of the sorption of Se(VI) with respect to the one expected (additivityreaction).This study has shown that, knowing only the element composition of the soil, it is not sufficient to evaluate thesorption of selenate without any experimentation.TOULON-Bibliotheque electronique (830629901) / SudocSudocFranceF
The addition of silver affects the deformation mechanism of a twinninginduced plasticity steel: Potential for thinner degradable stents
While Fe-based alloys have already been reported to possess all mechanical properties required for vascular stenting, their relatively low degradation rate in vivo still constitutes their main bottleneck. The inflammatory reaction generated by a stent is inversely proportional to its mass. Therefore, the tendency in stenting is to lower the section so to reduce the inflammatory reaction. Twinning-induced plasticity steels (TWIP) possess excellent mechanical properties for envisaging the next generation of thinner degradable cardiovascular stents. To accelerate the degradation, the addition of noble elements was proposed, aimed at promoting corrosion by galvanic coupling. In this context, silver was reported to generally increase the degradation rate. However, its impact on the deformation mechanism of TWIP steels has not been reported yet. Results show that the use of Ag significantly reduces the ductility without altering the strength of the material. Furthermore, the presence of Ag was found to promote a different deformation texture, thus stimulating the formation of mechanical martensite. Since a stent works in the deformed state, understanding the microstructure and texture resulting from plastic deformation can effectively help to forecast the degradation mechanisms taking place during implantation and the expected degradation time. Moreover, knowing the deformed microstructure allows to understand the formability of very small tubes, as precursors of the next generation of thin section degradable stents
Interdependence of structural and electrical properties in tantalum/tantalum oxide multilayers
Dc reactive sputtering was used to deposit tantalum metal/oxide periodic nanometric multilayers using the innovative technique namely, the reactive ga
FAS-L, IL-10, and double-negative CD4- CD8- TCR alpha/beta+ T cells are reliable markers of autoimmune lymphoproliferative syndrome (ALPS) associated with FAS loss of function.
Autoimmune lymphoproliferative syndrome (ALPS) is characterized by splenomegaly, lymphadenopathy, hypergammaglobulinemia, accumulation of double-negative TCRalphabeta(+) CD4(-)CD8(-) T cells (DNT cells), and autoimmunity. Previously, DNT cell detection and a functional defect of T cells in a FAS-induced apoptosis test in vitro had been used for ALPS diagnosis. However, a functional defect can also be detected in mutation-positive relatives (MPRs) who remain free of any ALPS-related disease. In contrast, lymphocytes from patients carrying a somatic mutation of FAS exhibit normal sensitivity to FAS-induced apoptosis in vitro. We assessed the soluble FAS-L concentration in the plasma of ALPS patients carrying FAS mutations. Overall, we showed that determination of the FAS-L represents, together with the IL-10 concentration and the DNT cell percentage, a reliable tool for the diagnosis of ALPS.Evaluation StudiesJournal ArticleResearch Support, Non-U.S. Gov'tSCOPUS: ar.jinfo:eu-repo/semantics/publishe