Pierre Glynn | United States Geological Survey (original) (raw)

Papers by Pierre Glynn

Research paper thumbnail of Modeling Np and Pu transport with a surface complexation model and spatially variant sorption capacities: implications for reactive transport modeling and performance assessments of nuclear waste disposal sites

Computers & Geosciences, 2003

One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciat... more One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr

Research paper thumbnail of Hydraulic and Geochemical Framework of the Idaho National Engineering and Environmental Laboratory Vadose Zone

Vadose Zone Journal, 2004

Research paper thumbnail of Reply to Dr. Stoesselfs Comment on

Geochimica Et Cosmochimica Acta, 1992

In reply to the Critical Comment of R. K. Stoessell (this issue), limiting activity coefficients ... more In reply to the Critical Comment of R. K. Stoessell (this issue), limiting activity coefficients of bromide in halite ( γNaBr) have been calculated by least-squares fitting of SIMONS et al.'s (1952) bromide distribution coefficient data for the Na(Cl,Br)-NaOH-H 2O system at 35°C. Regular and subregular solidsolution model fits give γNaBr = 7.4 and γNaBr = 8.8, respectively. The Br contents of halite at equilibrium with seawater at initial halite saturation, calculated from the regular and subregular fits, are 17 ppm and 14 ppm, respectively. A survey of literature data for trace bromide in halite shows a wide spread in distribution coefficients, with lower values ( DBr≈ 0.01) reported by BLOCH and SCHNERB (1953), PUCHELT et al. (1972), and LUTZ (1975), and higher values ( DBr- ≈ 0.03) reported by BRAITSCH and HERRMANN (1963), KüHN (1968), HERRMANN (1972), HERRMANN (1980), MCCAFFREY et al. (1987), VALIASHKO et al. (1976), VALIASHKO and LAVROVA (1976), and Fontes (pers. commun., 1990). The measurement of stoichiometric saturation states for halite (or sylvite) with trace bromide mole-fractions is not practical, given the insensitivity of the measured solubilities on the bromide mole-fractions. Distribution coefficient measurements, with proof of thermodynamic equilibrium, need to be obtained instead, to conclusively determine the thermodynamic-mixing properties of both Na(Cl,Br) and K(Cl,Br) solidsolution series at very low mole-fractions of bromide. The applicability of the stoichiometric saturation concept to the interpretation of precipitation processes is questionable, primarily because the concept requires solid-solutions to behave as one-component solids with fixed composition. Lippmann diagrams are useful in depicting stoichiometric saturation, endmember saturation, and thermodynamic equilibrium states in binary-solid-solution aqueous-solution systems. Lippmann diagrams can contribute a better understanding of these systems, regardless of the concentration of the endmember components.

Research paper thumbnail of Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO 3 ) 2 - Ca (HCO 3 ) 2 - CO 2 -H 2 O solutions

Geochimica Et Cosmochimica Acta, 1992

Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO 2-saturated nonstoi... more Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO 2-saturated nonstoichiometric solutions of Sr(HC0 3 )2 and Ca(HC0 3 h at 25°C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca( HC0 3 )2solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr( HC0 3 h solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HC0 3 )2 solutions and 0-4 layers thick in Ca(HC0 3 )2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation ofa more stable Sr-rich solid. The compositions ofsecondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HC0 3 h and Ca(HC03h solutions, respectively. In Sr(HC0 3 )2 solutions, the XPS signal from the outer -60 Aon aragonite indicates a composition of 16 mol% SrC0 3 after only 2 min of contact, and 14-18 mol% SrCO) after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO J after 2 min of contact with Ca(HC0 3 h solution, and is 34-39 mol% CaC0 3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer -25 A(as much as 26 mol% SrC0 3 on aragonite and 44 mol% Caco 3 on strontianite). The results indicate rapid formation ofasolid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition ofthe bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component « Sr( HC0 3 )2) than in solutions spiked with the more soluble component (Ca(HCO J )2) , an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a nonstoichiometric surface reactive zone significantly decreases dissolution rates.

Research paper thumbnail of Geochemistry and the understanding of ground-water systems

Hydrogeology Journal, 2005

Geochemistry has contributed significantly to the understanding of ground-water systems over the ... more Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years. Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating. Other hydrochemical concepts, tools, and techniques have helped elucidate mechanisms of flow and transport in ground-water systems, and have helped unlock an archive of paleoenvironmental information. Hydrochemical and isotopic information can be used to interpret the origin and mode of ground-water recharge, refine estimates of time scales of recharge and ground-water flow, decipher reactive processes, provide paleohydrological information, and calibrate ground-water flow models. Progress needs to be made in obtaining representative samples. Improvements are needed in the interpretation of the information obtained, and in the construction and interpretation of numerical models utilizing hydrochemical data. The best approach will ensure an optimized iterative process between field data collection and analysis, interpretation, and the application of forward, inverse, and statistical modeling tools. Advances are anticipated from microbiological investigations, the characterization of natural organics, isotopic fingerprinting, applications of dissolved gas measurements, and the fields of reaction kinetics and coupled processes. A thermodynamic perspective is offered that could facilitate the comparison and understanding of the multiple physical, chemical, and biological processes affecting ground-water systems. La géochimie a contribué de façon importante à la compréhension des systèmes d’eaux souterraines pendant les 50 dernières années. Les avancées ont portées sur le développement du concept des faciès hydrochimiques, sur l’application de la théorie des équilibres, l’étude des processus d’oxydoréduction, et sur la datation au radiocarbone. D’autres concepts, outils et techniques, ont aidé à l’ élucidation des élucider les mécanismes d’écoulement et de transport dans les systèmes d’eaux souterraines, et à la compréhension des archives informations paléo-environnementales. Les informations hydrochimiques et isotopiques peuvent être utilisées pour interpréter l’origine et le mode de recharge des eaux souterraines, affiner l’estimation des temps de recharge et d’ écoulements, déchiffrer les processus de réaction, apporter une meilleure information paléohydrogéologique et calibrer les modèles d’écoulement des eaux souterraines. Beaucoup de progrès ont besoin d’être réalisés pour obtenir des échantillons représentatifs. Des améliorations sont nécessaires dans l’interprétation des informations obtenues, et dans la construction et l’interprétation de modèles numériques utilisant des données hydrochimiques. La meilleure approches arsurément un processus itératif optimisé entre la collection de données de terrain et l’analyse, l’interprétation, et l’application d’outils de modélisation statistique, inverse et direct. Des avancées sont anticipées par les dans le demeine des études microbiologiques, dans la caractérisation des matières organiques naturelles, le marquage isotopique, les mesures de gaz dissous, les réactions cinétiques la compréhension des couplages. Une perspectives thermodynamique pourraient faciliter la comparaison et la compréhension des multiples processus physiques, chimiques et biologiques qui affectent les systèmes hydrogéologiques. La geoquímica ha contribuido significativamente al entendimiento de los sistemas de aguas subterráneas durante los últimos 50 años. Entre los avances históricos puede incluirse el desarrollo del concento de facies hidroquímicas, la aplicación de la teoría de equilibrio, investigación de los procesos oxidación-reducción, y datación con radiocarbono. Otros conceptos, herramientas y técnicas hidroquímicas han ayudado a esclarecer los mecanismos de flujo y transporte en sistemas de agua subterránea, y han ayudado a descifrar un archivo de información paleoambiental. Información hidroquímica e isotópica puede utilizarse para interpretar el origen y modo de recarga de agua subterránea, descifrar procesos reactivos, aportar información paleohidrológica, y calibrar modelos de flujo de agua subterránea. Necesita avanzarse en la obtención de muestras representativas. Se necesitan mejoras en la interpretación de la información obtenida y en la construcción e interpretación de modelos numéricos que utilizan datos hidroquímicos. El mejor enfoque asegurará un proceso iterativo optimizado entre toma y análisis de datos de campo, interpretación, y la aplicación de herramientas de modelizado estadísticas, directas, e inversas. Se anticipan avances a partir de investigaciones microbiológicas, la caracterización de orgánicos naturales, caracterización isotópica, aplicaciones de mediciones de gas disuelto, y los campos de cinética de reacción y procesos acoplados. Se ofrece una perspectiva termodinámica que podría facilitar la comparación y entendimiento de los múltiples procesos físicos, químicos, y biológicos que afectan sistemas de aguas subterráneas.

Research paper thumbnail of Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems

Geochimica Et Cosmochimica Acta, 1990

Equations are presented deseribing equilibrium in binary solid-solution aqueous-solution (SSAS) s... more Equations are presented deseribing equilibrium in binary solid-solution aqueous-solution (SSAS) systems after a dissolution. precipitation. or recrystallization process. as a function of the composition and relative proportion of the initial phases. Equilibrium phase diagrams incorporating the concept of stoichiometric saturation are used to interpret possible reaction paths and to demonstrate relations between stoichiometric saturation. primary saturation. and thermodynamic equilibrium states.

Research paper thumbnail of Geochemistry and the understanding of ground-water systems

Hydrogeology Journal, 2005

Geochemistry has contributed significantly to the understanding of ground-water systems over the ... more Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years. Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating. Other hydrochemical concepts, tools, and techniques have helped elucidate mechanisms of flow and transport in ground-water systems, and have helped unlock an archive of paleoenvironmental information. Hydrochemical and isotopic information can be used to interpret the origin and mode of ground-water recharge, refine estimates of time scales of recharge and ground-water flow, decipher reactive processes, provide paleohydrological information, and calibrate ground-water flow models. Progress needs to be made in obtaining representative samples. Improvements are needed in the interpretation of the information obtained, and in the construction and interpretation of numerical models utilizing hydrochemical data. The best approach will ensure an optimized iterative process between field data collection and analysis, interpretation, and the application of forward, inverse, and statistical modeling tools. Advances are anticipated from microbiological investigations, the characterization of natural organics, isotopic fingerprinting, applications of dissolved gas measurements, and the fields of reaction kinetics and coupled processes. A thermodynamic perspective is offered that could facilitate the comparison and understanding of the multiple physical, chemical, and biological processes affecting ground-water systems. La géochimie a contribué de façon importante à la compréhension des systèmes d'eaux souterraines pendant les 50 dernières années. Les avancées ont portées sur le développement du concept des faciès hydrochimiques, sur l'application de la théorie des équilibres, l'étude des processus d'oxydoréduction, et sur la datation au radiocarbone. D'autres concepts, outils et techniques, ont aidé à l' élucidation des élucider les mécanismes d'écoulement et de transport dans les systèmes d'eaux souterraines, et à la compréhension des archives informations paléo-environnementales. Les informations hydrochimiques et isotopiques peuvent être utilisées pour interpréter l'origine et le mode de recharge des eaux souterraines, affiner l'estimation des temps de recharge et d' écoulements, déchiffrer les processus de réaction, apporter une meilleure information paléohydrogéologique et calibrer les modèles d'écoulement des eaux souterraines. Beaucoup de progrès ont besoin d'être réalisés pour obtenir des échantillons représentatifs. Des améliorations sont nécessaires dans l'interprétation des informations obtenues, et dans la construction et l'interprétation de modèles numériques utilisant des données hydrochimiques. La meilleure approches arsurément un processus itératif optimisé entre la collection de données de terrain et l'analyse, l'interprétation, et l'application d'outils de modélisation statistique, inverse et direct. Des avancées sont anticipées par les dans le demeine des études microbiologiques, dans la caractérisation des matières organiques naturelles, le marquage isotopique, les mesures de gaz dissous, les réactions cinétiques la compréhension des couplages. Une perspectives thermodynamique pourraient faciliter la comparaison et la compréhension des multiples processus physiques, chimiques et biologiques qui affectent les systèmes hydrogéologiques. La geoquímica ha contribuido significativamente al entendimiento de los sistemas de aguas subterráneas durante los últimos 50 años. Entre los avances históricos puede incluirse el desarrollo del concento de facies hidroquímicas, la aplicación de la teoría de equilibrio, investigación de los procesos oxidación-reducción, y datación con radiocarbono. Otros conceptos, herramientas y técnicas hidroquímicas han ayudado a esclarecer los mecanismos de flujo y transporte en sistemas de agua subterránea, y han ayudado a descifrar un archivo de información paleoambiental. Información hidroquímica e isotópica puede utilizarse para interpretar el origen y modo de recarga de agua subterránea, descifrar procesos reactivos, aportar información paleohidrológica, y calibrar modelos de flujo de agua subterránea. Necesita avanzarse en la obtención de muestras representativas. Se necesitan mejoras en la interpretación de la información obtenida y en la construcción e interpretación de modelos numéricos que utilizan datos hidroquímicos. El mejor enfoque asegurará un proceso iterativo optimizado entre toma y análisis de datos de campo, interpretación, y la aplicación de herramientas de modelizado estadísticas, directas, e inversas. Se anticipan avancesa partir de investigaciones microbiológicas, la caracterización de orgánicos naturales, caracterización isotópica, aplicaciones de mediciones de gas disuelto, y los campos de cinética de reacción y procesos acoplados. Se ofrece una perspectiva termodinámica que podría facilitar la comparación y entendimiento de los múltiples procesos físicos, químicos, y biológicos que afectan sistemas de aguas subterráneas.

Research paper thumbnail of Kinetic dissolution of carbonates and Mn oxides in acidic water: measurement of in situ field rates and reactive transport modeling

Applied Geochemistry, 2003

The kinetics of carbonate and Mn oxide dissolution under acidic conditions were examined through ... more The kinetics of carbonate and Mn oxide dissolution under acidic conditions were examined through the in situ exposure of pure phase samples to acidic ground water in Pinal Creek Basin, Arizona. The average long-term calculated in situ dissolution rates for calcite and dolomite were 1.65Â10 À7 and 3.64Â10 À10 mmol/(cm 2 s), respectively, which were about 3 orders of magnitude slower than rates derived in laboratory experiments by other investigators. Application of both in situ and lab-derived calcite and dolomite dissolution rates to equilibrium reactive transport simulations of a column experiment did not improve the fit to measured outflow chemistry: at the spatial and temporal scales of the column experiment, the use of an equilibrium model adequately simulated carbonate dissolution in the column. Pyrolusite (MnO 2 ) exposed to acidic ground water for 595 days increased slightly in weight despite thermodynamic conditions that favored dissolution. This result might be related to a recent finding by another investigator that the reductive dissolution of pyrolusite is accompanied by the precipitation of a mixed Mn-Fe oxide species. In PHREEQC reactive transport simulations, the incorporation of Mn kinetics improved the fit between observed and simulated behavior at the column and field scales, although the column-fitted rate for Mn-oxide dissolution was about 4 orders of magnitude greater than the field-fitted rate. Remaining differences between observed and simulated contaminant transport trends at the Pinal Creek site were likely related to factors other than the Mn oxide dissolution rate, such as the concentration of Fe oxide surface sites available for adsorption, the effects of competition among dissolved species for available surface sites, or reactions not included in the model.

Research paper thumbnail of Reactive transport of metal contaminants in alluvium—model comparison and column simulation

Applied Geochemistry, 2000

A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was do... more A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was done to determine the suitability of each for simulating the movement of acidic contamination in alluvium. For simulations that accounted for aqueous complexation, precipitation and dissolution, the breakthrough and rinseout curves generated by each model were similar. The dierences in simulated equilibrium concentrations between models were minor and were related to (1) dierent units in model output, (2) dierent activity coecients, and ionic-strength calculations. When adsorption processes were added to the models, the rinseout pH simulated by PHREEQC using the diuse double-layer adsorption model rose to a pH of 6 after pore volume 15, about 1 pore volume later than the pH simulated by HGC using the constant-capacitance model.

Research paper thumbnail of Corrigendum to “Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona

Journal of Hydrology, 1999

Corrigendum to "Analysis and simulation of reactive transport of metal contaminants in ground wat... more Corrigendum to "Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona" ଝ [

Research paper thumbnail of Geochemistry and Reactive Transport of Metal Contaminants in Ground Water, Pinal Creek Basin, Arizona

Activities related to more than a century of large-scale copper mining in the Pinal Creek Basin i... more Activities related to more than a century of large-scale copper mining in the Pinal Creek Basin in central Arizona have contaminated the regional alluvial aquifer and perennial streamflow with acidity and metals. Water-chemistry and solid-phase analyses and computer-aided geochemical modeling were used to understand the evolution of the ground-water plume between 1984 and 1998. The ground-water plume consists of three hydrochemical zones: (1) an acidic zone, which contains large concentrations of metals and has a pH that ranges from 3.6 to about 5; (2) a transition zone where carbonate-mineral dissolution causes pH to increase to above 5, which results in the precipitation of iron hydroxide and the adsorption of trace metals such as nickel and zinc; and (3) a neutralized zone, which contains large concentrations of manganese, calcium, and sulfate, and has a pH of about 6 to 7. Inverse geochemical modeling using NET-PATH revealed that, in addition to calcite dissolution, silicate dissolution was required to account for the mass transfers of calcium and magnesium across the transition zone. Analysis of the measured changes in plume geochemistry was aided by PHREEQC reactive-transport modeling, which helped determine that oxidation-reduction reactions were significant in the acidic zone of the plume through the late 1980's. The local equilibrium assumption required by reactive-transport modeling probably was invalid for oxidationreduction reactions that involved manganese and, to a lesser extent, neutralization reactions that involved calcite. Sensitivity analyses indicated that the rate of advance of the pH front was highly sensitive to the initial calcite concentration, and that ground water along a flow path near the base of the alluvium was in partial or indirect contact with the atmosphere, possibly through mixing with shallower water.

Research paper thumbnail of Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona

Journal of Hydrology, 1998

Large-scale mining activities have generated a plume of acidic ground water more than 15 km long ... more Large-scale mining activities have generated a plume of acidic ground water more than 15 km long in the regional aquifer of the Pinal Creek Basin. A one-dimensional reactive-transport model was developed using PHREEQC to aid in the analysis of transport and chemical processes in the plume and to determine the uses and limitations of this type of modeling approach. In 1984, the acidic part of the plume had a pH as low as 3.4 and contained milligram-per-liter concentrations of iron, copper, aluminum and other metals. From 1984 to 1994, concentrations of contaminants in the alluvial aquifer in Pinal Creek Basin, Arizona, decreased as a result of mixing, recharge, remedial pumping and chemical reactions. For reactions involving gypsum and rhodochrosite, the equilibrium modeling assumption of a local geochemical equilibrium was generally valid. From 1984 to 1990, water along the simulated flow path was at equilibrium or slightly supersaturated with gypsum, and gypsum equilibria controlled dissolved concentrations of calcium and sulfate. Beginning in 1991, water in the acidic part of the plume became increasingly undersaturated with respect to gypsum, indicating that the gypsum available for dissolution in the aquifer may have been completely consumed by about 1991. Rhodochrosite precipitation was thought responsible for the measured attenuation in dissolved manganese in the neutralized zone.

Research paper thumbnail of Modeling Np and Pu transport with a surface complexation model and spatially variant sorption capacities: implications for reactive transport modeling and performance assessments of nuclear waste disposal sites

Computers & Geosciences, 2003

One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciat... more One-dimensional (1D) geochemical transport modeling is used to demonstrate the effects of speciation and sorption reactions on the ground-water transport of Np and Pu, two redox-sensitive elements. Earlier 1D simulations (Reardon, 1981) considered the kinetically limited dissolution of calcite and its effect on ion-exchange reactions (involving 90Sr, Ca, Na, Mg and K), and documented the spatial variation of a 90Sr

Research paper thumbnail of Hydraulic and Geochemical Framework of the Idaho National Engineering and Environmental Laboratory Vadose Zone

Vadose Zone Journal, 2004

Research paper thumbnail of Reply to Dr. Stoesselfs Comment on

Geochimica Et Cosmochimica Acta, 1992

In reply to the Critical Comment of R. K. Stoessell (this issue), limiting activity coefficients ... more In reply to the Critical Comment of R. K. Stoessell (this issue), limiting activity coefficients of bromide in halite ( γNaBr) have been calculated by least-squares fitting of SIMONS et al.'s (1952) bromide distribution coefficient data for the Na(Cl,Br)-NaOH-H 2O system at 35°C. Regular and subregular solidsolution model fits give γNaBr = 7.4 and γNaBr = 8.8, respectively. The Br contents of halite at equilibrium with seawater at initial halite saturation, calculated from the regular and subregular fits, are 17 ppm and 14 ppm, respectively. A survey of literature data for trace bromide in halite shows a wide spread in distribution coefficients, with lower values ( DBr≈ 0.01) reported by BLOCH and SCHNERB (1953), PUCHELT et al. (1972), and LUTZ (1975), and higher values ( DBr- ≈ 0.03) reported by BRAITSCH and HERRMANN (1963), KüHN (1968), HERRMANN (1972), HERRMANN (1980), MCCAFFREY et al. (1987), VALIASHKO et al. (1976), VALIASHKO and LAVROVA (1976), and Fontes (pers. commun., 1990). The measurement of stoichiometric saturation states for halite (or sylvite) with trace bromide mole-fractions is not practical, given the insensitivity of the measured solubilities on the bromide mole-fractions. Distribution coefficient measurements, with proof of thermodynamic equilibrium, need to be obtained instead, to conclusively determine the thermodynamic-mixing properties of both Na(Cl,Br) and K(Cl,Br) solidsolution series at very low mole-fractions of bromide. The applicability of the stoichiometric saturation concept to the interpretation of precipitation processes is questionable, primarily because the concept requires solid-solutions to behave as one-component solids with fixed composition. Lippmann diagrams are useful in depicting stoichiometric saturation, endmember saturation, and thermodynamic equilibrium states in binary-solid-solution aqueous-solution systems. Lippmann diagrams can contribute a better understanding of these systems, regardless of the concentration of the endmember components.

Research paper thumbnail of Dissolution of aragonite-strontianite solid solutions in nonstoichiometric Sr (HCO 3 ) 2 - Ca (HCO 3 ) 2 - CO 2 -H 2 O solutions

Geochimica Et Cosmochimica Acta, 1992

Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO 2-saturated nonstoi... more Synthetic strontianite-aragonite solid-solution minerals were dissolved in CO 2-saturated nonstoichiometric solutions of Sr(HC0 3 )2 and Ca(HC0 3 h at 25°C. The results show that none of the dissolution reactions reach thermodynamic equilibrium. Congruent dissolution in Ca( HC0 3 )2solutions either attains or closely approaches stoichiometric saturation with respect to the dissolving solid. In Sr( HC0 3 h solutions the reactions usually become incongruent, precipitating a Sr-rich phase before reaching stoichiometric saturation. Dissolution of mechanical mixtures of solids approaches stoichiometric saturation with respect to the least stable solid in the mixture. Surface uptake from subsaturated bulk solutions was observed in the initial minutes of dissolution. This surficial phase is 0-10 atomic layers thick in Sr(HC0 3 )2 solutions and 0-4 layers thick in Ca(HC0 3 )2 solutions, and subsequently dissolves and/or recrystallizes, usually within 6 min of reaction. The initial transient surface precipitation (recrystallization) process is followed by congruent dissolution of the original solid which proceeds to stoichiometric saturation, or until the precipitation ofa more stable Sr-rich solid. The compositions ofsecondary precipitates do not correspond to thermodynamic equilibrium or stoichiometric saturation states. X-ray photoelectron spectroscopy (XPS) measurements indicate the formation of solid solutions on surfaces of aragonite and strontianite single crystals immersed in Sr(HC0 3 h and Ca(HC03h solutions, respectively. In Sr(HC0 3 )2 solutions, the XPS signal from the outer -60 Aon aragonite indicates a composition of 16 mol% SrC0 3 after only 2 min of contact, and 14-18 mol% SrCO) after 3 weeks of contact. The strontianite surface averages approximately 22 mol% CaCO J after 2 min of contact with Ca(HC0 3 h solution, and is 34-39 mol% CaC0 3 after 3 weeks of contact. XPS analysis suggests the surface composition is zoned with somewhat greater enrichment in the outer -25 A(as much as 26 mol% SrC0 3 on aragonite and 44 mol% Caco 3 on strontianite). The results indicate rapid formation ofasolid-solution surface phase from subsaturated aqueous solutions. The surface phase continually adjusts in composition in response to changes in composition ofthe bulk fluid as net dissolution proceeds. Dissolution rates of the endmembers are greatly reduced in nonstoichiometric solutions relative to dissolution rates observed in stoichiometric solutions. All solids dissolve more slowly in solutions spiked with the least soluble component « Sr( HC0 3 )2) than in solutions spiked with the more soluble component (Ca(HCO J )2) , an effect that becomes increasingly significant as stoichiometric saturation is approached. It is proposed that the formation of a nonstoichiometric surface reactive zone significantly decreases dissolution rates.

Research paper thumbnail of Geochemistry and the understanding of ground-water systems

Hydrogeology Journal, 2005

Geochemistry has contributed significantly to the understanding of ground-water systems over the ... more Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years. Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating. Other hydrochemical concepts, tools, and techniques have helped elucidate mechanisms of flow and transport in ground-water systems, and have helped unlock an archive of paleoenvironmental information. Hydrochemical and isotopic information can be used to interpret the origin and mode of ground-water recharge, refine estimates of time scales of recharge and ground-water flow, decipher reactive processes, provide paleohydrological information, and calibrate ground-water flow models. Progress needs to be made in obtaining representative samples. Improvements are needed in the interpretation of the information obtained, and in the construction and interpretation of numerical models utilizing hydrochemical data. The best approach will ensure an optimized iterative process between field data collection and analysis, interpretation, and the application of forward, inverse, and statistical modeling tools. Advances are anticipated from microbiological investigations, the characterization of natural organics, isotopic fingerprinting, applications of dissolved gas measurements, and the fields of reaction kinetics and coupled processes. A thermodynamic perspective is offered that could facilitate the comparison and understanding of the multiple physical, chemical, and biological processes affecting ground-water systems. La géochimie a contribué de façon importante à la compréhension des systèmes d’eaux souterraines pendant les 50 dernières années. Les avancées ont portées sur le développement du concept des faciès hydrochimiques, sur l’application de la théorie des équilibres, l’étude des processus d’oxydoréduction, et sur la datation au radiocarbone. D’autres concepts, outils et techniques, ont aidé à l’ élucidation des élucider les mécanismes d’écoulement et de transport dans les systèmes d’eaux souterraines, et à la compréhension des archives informations paléo-environnementales. Les informations hydrochimiques et isotopiques peuvent être utilisées pour interpréter l’origine et le mode de recharge des eaux souterraines, affiner l’estimation des temps de recharge et d’ écoulements, déchiffrer les processus de réaction, apporter une meilleure information paléohydrogéologique et calibrer les modèles d’écoulement des eaux souterraines. Beaucoup de progrès ont besoin d’être réalisés pour obtenir des échantillons représentatifs. Des améliorations sont nécessaires dans l’interprétation des informations obtenues, et dans la construction et l’interprétation de modèles numériques utilisant des données hydrochimiques. La meilleure approches arsurément un processus itératif optimisé entre la collection de données de terrain et l’analyse, l’interprétation, et l’application d’outils de modélisation statistique, inverse et direct. Des avancées sont anticipées par les dans le demeine des études microbiologiques, dans la caractérisation des matières organiques naturelles, le marquage isotopique, les mesures de gaz dissous, les réactions cinétiques la compréhension des couplages. Une perspectives thermodynamique pourraient faciliter la comparaison et la compréhension des multiples processus physiques, chimiques et biologiques qui affectent les systèmes hydrogéologiques. La geoquímica ha contribuido significativamente al entendimiento de los sistemas de aguas subterráneas durante los últimos 50 años. Entre los avances históricos puede incluirse el desarrollo del concento de facies hidroquímicas, la aplicación de la teoría de equilibrio, investigación de los procesos oxidación-reducción, y datación con radiocarbono. Otros conceptos, herramientas y técnicas hidroquímicas han ayudado a esclarecer los mecanismos de flujo y transporte en sistemas de agua subterránea, y han ayudado a descifrar un archivo de información paleoambiental. Información hidroquímica e isotópica puede utilizarse para interpretar el origen y modo de recarga de agua subterránea, descifrar procesos reactivos, aportar información paleohidrológica, y calibrar modelos de flujo de agua subterránea. Necesita avanzarse en la obtención de muestras representativas. Se necesitan mejoras en la interpretación de la información obtenida y en la construcción e interpretación de modelos numéricos que utilizan datos hidroquímicos. El mejor enfoque asegurará un proceso iterativo optimizado entre toma y análisis de datos de campo, interpretación, y la aplicación de herramientas de modelizado estadísticas, directas, e inversas. Se anticipan avances a partir de investigaciones microbiológicas, la caracterización de orgánicos naturales, caracterización isotópica, aplicaciones de mediciones de gas disuelto, y los campos de cinética de reacción y procesos acoplados. Se ofrece una perspectiva termodinámica que podría facilitar la comparación y entendimiento de los múltiples procesos físicos, químicos, y biológicos que afectan sistemas de aguas subterráneas.

Research paper thumbnail of Reaction paths and equilibrium end-points in solid-solution aqueous-solution systems

Geochimica Et Cosmochimica Acta, 1990

Equations are presented deseribing equilibrium in binary solid-solution aqueous-solution (SSAS) s... more Equations are presented deseribing equilibrium in binary solid-solution aqueous-solution (SSAS) systems after a dissolution. precipitation. or recrystallization process. as a function of the composition and relative proportion of the initial phases. Equilibrium phase diagrams incorporating the concept of stoichiometric saturation are used to interpret possible reaction paths and to demonstrate relations between stoichiometric saturation. primary saturation. and thermodynamic equilibrium states.

Research paper thumbnail of Geochemistry and the understanding of ground-water systems

Hydrogeology Journal, 2005

Geochemistry has contributed significantly to the understanding of ground-water systems over the ... more Geochemistry has contributed significantly to the understanding of ground-water systems over the last 50 years. Historic advances include development of the hydrochemical facies concept, application of equilibrium theory, investigation of redox processes, and radiocarbon dating. Other hydrochemical concepts, tools, and techniques have helped elucidate mechanisms of flow and transport in ground-water systems, and have helped unlock an archive of paleoenvironmental information. Hydrochemical and isotopic information can be used to interpret the origin and mode of ground-water recharge, refine estimates of time scales of recharge and ground-water flow, decipher reactive processes, provide paleohydrological information, and calibrate ground-water flow models. Progress needs to be made in obtaining representative samples. Improvements are needed in the interpretation of the information obtained, and in the construction and interpretation of numerical models utilizing hydrochemical data. The best approach will ensure an optimized iterative process between field data collection and analysis, interpretation, and the application of forward, inverse, and statistical modeling tools. Advances are anticipated from microbiological investigations, the characterization of natural organics, isotopic fingerprinting, applications of dissolved gas measurements, and the fields of reaction kinetics and coupled processes. A thermodynamic perspective is offered that could facilitate the comparison and understanding of the multiple physical, chemical, and biological processes affecting ground-water systems. La géochimie a contribué de façon importante à la compréhension des systèmes d'eaux souterraines pendant les 50 dernières années. Les avancées ont portées sur le développement du concept des faciès hydrochimiques, sur l'application de la théorie des équilibres, l'étude des processus d'oxydoréduction, et sur la datation au radiocarbone. D'autres concepts, outils et techniques, ont aidé à l' élucidation des élucider les mécanismes d'écoulement et de transport dans les systèmes d'eaux souterraines, et à la compréhension des archives informations paléo-environnementales. Les informations hydrochimiques et isotopiques peuvent être utilisées pour interpréter l'origine et le mode de recharge des eaux souterraines, affiner l'estimation des temps de recharge et d' écoulements, déchiffrer les processus de réaction, apporter une meilleure information paléohydrogéologique et calibrer les modèles d'écoulement des eaux souterraines. Beaucoup de progrès ont besoin d'être réalisés pour obtenir des échantillons représentatifs. Des améliorations sont nécessaires dans l'interprétation des informations obtenues, et dans la construction et l'interprétation de modèles numériques utilisant des données hydrochimiques. La meilleure approches arsurément un processus itératif optimisé entre la collection de données de terrain et l'analyse, l'interprétation, et l'application d'outils de modélisation statistique, inverse et direct. Des avancées sont anticipées par les dans le demeine des études microbiologiques, dans la caractérisation des matières organiques naturelles, le marquage isotopique, les mesures de gaz dissous, les réactions cinétiques la compréhension des couplages. Une perspectives thermodynamique pourraient faciliter la comparaison et la compréhension des multiples processus physiques, chimiques et biologiques qui affectent les systèmes hydrogéologiques. La geoquímica ha contribuido significativamente al entendimiento de los sistemas de aguas subterráneas durante los últimos 50 años. Entre los avances históricos puede incluirse el desarrollo del concento de facies hidroquímicas, la aplicación de la teoría de equilibrio, investigación de los procesos oxidación-reducción, y datación con radiocarbono. Otros conceptos, herramientas y técnicas hidroquímicas han ayudado a esclarecer los mecanismos de flujo y transporte en sistemas de agua subterránea, y han ayudado a descifrar un archivo de información paleoambiental. Información hidroquímica e isotópica puede utilizarse para interpretar el origen y modo de recarga de agua subterránea, descifrar procesos reactivos, aportar información paleohidrológica, y calibrar modelos de flujo de agua subterránea. Necesita avanzarse en la obtención de muestras representativas. Se necesitan mejoras en la interpretación de la información obtenida y en la construcción e interpretación de modelos numéricos que utilizan datos hidroquímicos. El mejor enfoque asegurará un proceso iterativo optimizado entre toma y análisis de datos de campo, interpretación, y la aplicación de herramientas de modelizado estadísticas, directas, e inversas. Se anticipan avancesa partir de investigaciones microbiológicas, la caracterización de orgánicos naturales, caracterización isotópica, aplicaciones de mediciones de gas disuelto, y los campos de cinética de reacción y procesos acoplados. Se ofrece una perspectiva termodinámica que podría facilitar la comparación y entendimiento de los múltiples procesos físicos, químicos, y biológicos que afectan sistemas de aguas subterráneas.

Research paper thumbnail of Kinetic dissolution of carbonates and Mn oxides in acidic water: measurement of in situ field rates and reactive transport modeling

Applied Geochemistry, 2003

The kinetics of carbonate and Mn oxide dissolution under acidic conditions were examined through ... more The kinetics of carbonate and Mn oxide dissolution under acidic conditions were examined through the in situ exposure of pure phase samples to acidic ground water in Pinal Creek Basin, Arizona. The average long-term calculated in situ dissolution rates for calcite and dolomite were 1.65Â10 À7 and 3.64Â10 À10 mmol/(cm 2 s), respectively, which were about 3 orders of magnitude slower than rates derived in laboratory experiments by other investigators. Application of both in situ and lab-derived calcite and dolomite dissolution rates to equilibrium reactive transport simulations of a column experiment did not improve the fit to measured outflow chemistry: at the spatial and temporal scales of the column experiment, the use of an equilibrium model adequately simulated carbonate dissolution in the column. Pyrolusite (MnO 2 ) exposed to acidic ground water for 595 days increased slightly in weight despite thermodynamic conditions that favored dissolution. This result might be related to a recent finding by another investigator that the reductive dissolution of pyrolusite is accompanied by the precipitation of a mixed Mn-Fe oxide species. In PHREEQC reactive transport simulations, the incorporation of Mn kinetics improved the fit between observed and simulated behavior at the column and field scales, although the column-fitted rate for Mn-oxide dissolution was about 4 orders of magnitude greater than the field-fitted rate. Remaining differences between observed and simulated contaminant transport trends at the Pinal Creek site were likely related to factors other than the Mn oxide dissolution rate, such as the concentration of Fe oxide surface sites available for adsorption, the effects of competition among dissolved species for available surface sites, or reactions not included in the model.

Research paper thumbnail of Reactive transport of metal contaminants in alluvium—model comparison and column simulation

Applied Geochemistry, 2000

A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was do... more A comparative assessment of two reactive-transport models, PHREEQC and HYDROGEOCHEM (HGC), was done to determine the suitability of each for simulating the movement of acidic contamination in alluvium. For simulations that accounted for aqueous complexation, precipitation and dissolution, the breakthrough and rinseout curves generated by each model were similar. The dierences in simulated equilibrium concentrations between models were minor and were related to (1) dierent units in model output, (2) dierent activity coecients, and ionic-strength calculations. When adsorption processes were added to the models, the rinseout pH simulated by PHREEQC using the diuse double-layer adsorption model rose to a pH of 6 after pore volume 15, about 1 pore volume later than the pH simulated by HGC using the constant-capacitance model.

Research paper thumbnail of Corrigendum to “Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona

Journal of Hydrology, 1999

Corrigendum to "Analysis and simulation of reactive transport of metal contaminants in ground wat... more Corrigendum to "Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona" ଝ [

Research paper thumbnail of Geochemistry and Reactive Transport of Metal Contaminants in Ground Water, Pinal Creek Basin, Arizona

Activities related to more than a century of large-scale copper mining in the Pinal Creek Basin i... more Activities related to more than a century of large-scale copper mining in the Pinal Creek Basin in central Arizona have contaminated the regional alluvial aquifer and perennial streamflow with acidity and metals. Water-chemistry and solid-phase analyses and computer-aided geochemical modeling were used to understand the evolution of the ground-water plume between 1984 and 1998. The ground-water plume consists of three hydrochemical zones: (1) an acidic zone, which contains large concentrations of metals and has a pH that ranges from 3.6 to about 5; (2) a transition zone where carbonate-mineral dissolution causes pH to increase to above 5, which results in the precipitation of iron hydroxide and the adsorption of trace metals such as nickel and zinc; and (3) a neutralized zone, which contains large concentrations of manganese, calcium, and sulfate, and has a pH of about 6 to 7. Inverse geochemical modeling using NET-PATH revealed that, in addition to calcite dissolution, silicate dissolution was required to account for the mass transfers of calcium and magnesium across the transition zone. Analysis of the measured changes in plume geochemistry was aided by PHREEQC reactive-transport modeling, which helped determine that oxidation-reduction reactions were significant in the acidic zone of the plume through the late 1980's. The local equilibrium assumption required by reactive-transport modeling probably was invalid for oxidationreduction reactions that involved manganese and, to a lesser extent, neutralization reactions that involved calcite. Sensitivity analyses indicated that the rate of advance of the pH front was highly sensitive to the initial calcite concentration, and that ground water along a flow path near the base of the alluvium was in partial or indirect contact with the atmosphere, possibly through mixing with shallower water.

Research paper thumbnail of Analysis and simulation of reactive transport of metal contaminants in ground water in Pinal Creek Basin, Arizona

Journal of Hydrology, 1998

Large-scale mining activities have generated a plume of acidic ground water more than 15 km long ... more Large-scale mining activities have generated a plume of acidic ground water more than 15 km long in the regional aquifer of the Pinal Creek Basin. A one-dimensional reactive-transport model was developed using PHREEQC to aid in the analysis of transport and chemical processes in the plume and to determine the uses and limitations of this type of modeling approach. In 1984, the acidic part of the plume had a pH as low as 3.4 and contained milligram-per-liter concentrations of iron, copper, aluminum and other metals. From 1984 to 1994, concentrations of contaminants in the alluvial aquifer in Pinal Creek Basin, Arizona, decreased as a result of mixing, recharge, remedial pumping and chemical reactions. For reactions involving gypsum and rhodochrosite, the equilibrium modeling assumption of a local geochemical equilibrium was generally valid. From 1984 to 1990, water along the simulated flow path was at equilibrium or slightly supersaturated with gypsum, and gypsum equilibria controlled dissolved concentrations of calcium and sulfate. Beginning in 1991, water in the acidic part of the plume became increasingly undersaturated with respect to gypsum, indicating that the gypsum available for dissolution in the aquifer may have been completely consumed by about 1991. Rhodochrosite precipitation was thought responsible for the measured attenuation in dissolved manganese in the neutralized zone.