Reaction Path Modeling Research Articles

광물성 약재(광물약)의 표준화에 관한 연구

광물성 약재(광물약)는 오랜 기간 동안 주로 중국, 한국 등 동양의 전통의학에서 화학성분이나 물리적인 성질이 질병치료나 건강 증진에 이용되어 왔던 단일 광물, 암석 및 생물화석 등을 의미한다. 광물성 약재는 산지의 지질특성, 기후 및 지표 환경에 의해 광물학적 특성이 달라지며, 광물의 조직, 수반광물, 정제 방법에 따라 약재로서의 효용성이 달라진다. 특히, 광물성 약재에 함유되어 있는 광물조성, 주성분 및 미량성분의 차이는 광물약의 약효와 유해성에 영향을 준다. 그러므로 광물약의 분석방법과 전처리 및 제조과정에 대한 표준화가 매우 중요하다. 광물성 약재에 함유된 유해 금속 원소는 수치(법제)나 탕약 제조 등 약제의 전처리 과정과 위와 장에서의 소화과정에서 성분이 변화되어 용출량이 결정되기 때문에 체내와 대응되는 조건에서의 적절한 시험방법을 정립하여, 그 결과에 의해 위액용출도, 인체흡수도, 안정성과 위해성이 평가되어야 한다. 또한, 광물성 약재의 안정성과 위해성을 평가할 수 있는 연구결과로 유효성분과 독성 물질의 체내 존재량을 예측할 수 있어야 한다. 연구에서 제안된 광물성 약재의 표준화 방법은 광물약의 개발과 활용에 유용한 기초자료로 이용될 뿐만 아니라, 광물성 약재의 품질 표준을 규격화 하는 기준을 제시해줄 것으로 기대된다. Oriental mineral medicines are single or mixture of more than one mineral species or rock/fossil which are used to treat disease. Mineral medicines remove harmful or useless substances to decrease toxicity and secondary effects, and cause the manufacture of medical compounds with increased efficacy. The extraction test is an accepted in vitro system to predict the bioaccessibility of major and minor elements from mineral medicine. It incorporates gastrointerstinal tract parameters representative of a human body that including stomach and small intestinal pH which are the same as digestion condition. The bioaccessibility of a mineral medicine is the fraction that is soluble in the gastrointestinal environment and is available for absorption. Reaction path modeling in the human body can predict digestion with gastric fluid as well as absorption in the small intestine, existence in body fluids and reaction progress of the exhaust process according to pH conditions in body. Also reaction path modeling can predict bioavailability, which is equal to existence rate in the body and the form and amount of a medicine in the body after intake. The study results from predicating the existence form mineral medicines in the body, and proving the effective ingredient using bioaccessibitily and human risk assessment, suggest these that should be necessary data for new medicine development.

The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skaftá river, Iceland

This study describes the chemical composition of dissolved, degased and suspended fluxes of the 2002 Skaftá glacial flood, which emerged from one of the Skaftá subglacial lake due to geothermal activity beneath the Icelandic Vatnajökull glacier. The dissolved and suspended fluxes during the flood are compared with those normally observed in the Skaftá river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters. Concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the Skaftá river. In addition, dissolved concentrations of nutrients such as SiO2, Fe, and V, increased more than an order of magnitude during the flood. These will affect biological processes on a local scale. The δ34S composition in the flood water suggests that the dissolved SO4 was derived from the oxidation of H2S and the geothermal fluid. The total suspended particulate load measured in the Skaftá river during the 8-day 2002 flood was approximately half of the non-flood total annual Skaftá suspended load. As particles carry the bulk of limiting nutrients to the oceans, this demonstrates the importance of glacial floods for primary production of coastal waters. The composition of the flood water and the Skaftá subglacial lake, together with reaction path modelling suggest that substantial degasing of CO2 and H2S occurred at the glacial outlet during the flood. This degasing may have released as much as 262,000 and 7,980tonnes of CO2 and H2S, respectively, to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event.

The Lost City hydrothermal system: Constraints imposed by vent fluid chemistry and reaction path models on subseafloor heat and mass transfer processes

Since the first reported discovery of the Lost City hydrothermal system in 2001, it was recognized that seawater alteration of ultramafic rocks plays a key role in the composition of the coexisting vent fluids. The unusually high pH and high concentrations of H2 and CH4 provide compelling evidence for this. Here we report the chemistry of hydrothermal fluids sampled from two vent structures (Beehive: ∼90–116°C, and M6: ∼75°C) at Lost City in 2008 during cruise KNOX18RR using ROV Jason 2 and R/V Revelle assets. The vent fluid chemistry at both sites reveals considerable overlap in concentrations of dissolved gases (H2, CH4), trace elements (Cs, Rb, Li, B and Sr), and major elements (SO4, Ca, K, Na, Cl), including a surprising decrease in dissolved Cl, suggesting a common source fluid is feeding both sites. The absence of Mg and relatively high concentrations of Ca and sulfate suggest solubility control by serpentine–diopside–anhydrite, while trace alkali concentrations, especially Rb and Cs, are high, assuming a depleted mantle protolith. In both cases, but especially for Beehive vent fluid, the silica concentrations are well in excess of those expected for peridotite alteration and the coexistence of serpentine–brucite at all reasonable temperatures. However, both the measured pH and silica values are in better agreement with serpentine–diopside–tremolite-equilibria. Geochemical modeling demonstrates that reaction of plagioclase with serpentinized peridotite can shift the chemical system away from brucite and into the tremolite stability field. This is consistent with the complex intermingling of peridotite and gabbroic bodies commonly observed within the Atlantis Massif. We speculate the existence of such plagioclase bearing peridotite may also account for the highly enriched trace alkali (Cs, Rb) concentrations in the Lost City vent fluids. Additionally, reactive transport modeling taking explicit account of temperature dependent rates of mineral dissolution and precipitation clarifies the feedback between permeability, heat loss, and changes in the dissolved Si of the vent fluids. Assuming both the Beehive and M6 vent fluids were sourced at similar subseafloor conditions (tremolite buffered at 200°C), model results indicate loss of approximately 30% Si upon cooling to ∼150°C during upflow. However, Si concentrations remained largely conservative with continued cooling to lower temperatures owing to unfavorable reaction kinetics. While consistent with the Beehive endmember composition, these results fail to explain the relative Si depletion in the lower temperature M6 fluids. Thus, it may be that more robust kinetic models for silicates are needed to accurately account for the mechanism and rate of silica removal in the unusually high pH of the Lost City vent fluids.

The pH of Enceladus’ ocean

Saturn’s moon, Enceladus, is a geologically active waterworld. The prevailing paradigm is that there is a subsurface ocean that erupts to the surface, which leads to the formation of a plume of vapor and ice above the south polar region. The chemistry of the ocean is just beginning to be understood, but is of profound geochemical and astrobiological interest. Here, we determine the pH of the ocean using a thermodynamic model of carbonate speciation. Observational data from the Cassini spacecraft are used to make a chemical model of ocean water on Enceladus. The model suggests that Enceladus’ ocean is a Na–Cl–CO3 solution with an alkaline pH of ∼11–12. The dominance of aqueous NaCl is a feature that Enceladus’ ocean shares with terrestrial seawater, but the ubiquity of dissolved Na2CO3 suggests that soda lakes are more analogous to the Enceladus ocean. The high pH implies that the hydroxide ion should be relatively abundant, while divalent metals should be present at low concentrations owing to buffering by carbonates and phyllosilicates on the ocean floor. Carboxyl groups in dissolved organic species would be negatively charged, while amino groups would exist predominately in the neutral form. Knowledge of the pH improves our understanding of geochemical processes in Enceladus’ ocean. The high pH is interpreted to be a key consequence of serpentinization of chondritic rock, as predicted by prior geochemical reaction path models; although degassing of CO2 from the ocean may also play a role depending on the efficiency of mixing processes in the ocean. Serpentinization leads to the generation of H2, a geochemical fuel that can support both abiotic and biological synthesis of organic molecules such as those that have been detected in Enceladus’ plume. Serpentinization and H2 generation should have occurred on Enceladus, like on the parent bodies of aqueously altered meteorites; but it is unknown whether these critical processes are still taking place, or if Enceladus’ rocky core has been completely altered by past hydrothermal activity. The presence of native H2 in the plume would provide strong evidence for contemporary aqueous alteration that replenishes this source of energy for possible life. The high pH also suggests that the delivery of strong oxidants from the surface to the ocean has not been significant (otherwise, sulfuric acid would be produced), which would be consistent with geophysical models of episodic resurfacing activity on Enceladus. This paper represents an expansion of chemical oceanography to an “ocean planet” beyond Earth.

Degassing regime of Hekla volcano 2012–2013

Hekla is a frequently active volcano with an infamously short pre-eruptive warning period. Our project contributes to the ongoing work on improving Hekla’s monitoring and early warning systems. In 2012 we began monitoring gas release at Hekla. The dataset comprises semi-permanent near-real time measurements with a MultiGAS system, quantification of diffuse gas flux, and direct samples analysed for composition and isotopes (δ13C, δD and δ18O). In addition, we used reaction path modelling to derive information on the origin and reaction pathways of the gas emissions.Hekla’s quiescent gas composition was CO2-dominated (0.8mol fraction) and the δ13C signature was consistent with published values for Icelandic magmas. The gas is poor in H2O and S compared to hydrothermal manifestations and syn-eruptive emissions from other active volcanic systems in Iceland. The total CO2 flux from Hekla central volcano (diffuse soil emissions) is at least 44Td−1, thereof 14Td−1 are sourced from a small area at the volcano’s summit. There was no detectable gas flux at other craters, even though some of them had higher ground temperatures and had erupted more recently.Our measurements are consistent with a magma reservoir at depth coupled with a shallow dike beneath the summit. In the current quiescent state, the composition of the exsolved gas is substantially modified along its pathway to the surface through cooling and interaction with wall-rock and groundwater. The modification involves both significant H2O condensation and scrubbing of S-bearing species, leading to a CO2-dominated gas emitted at the summit. We conclude that a compositional shift towards more S- and H2O-rich gas compositions if measured in the future by the permanent MultiGAS station should be viewed as sign of imminent volcanic unrest on Hekla.

Sedimentary reservoir oxidation during geologic CO2 sequestration

Injection of carbon dioxide into subsurface geologic reservoirs during geologic carbon sequestration (GCS) introduces an oxidizing supercritical CO2 phase into a subsurface geologic environment that is typically reducing. The resulting redox disequilibrium provides the chemical potential for the reduction of CO2 to lower free energy organic species. However, redox reactions involving carbon typically require the presence of a catalyst. Iron oxide minerals, including magnetite, are known to catalyze oxidation and reduction reactions of C-bearing species. If the redox conditions in the reservoir are modified by redox transformations involving CO2, such changes could also affect mineral stability, leading to dissolution and precipitation reactions and alteration of the long-term fate of CO2 in GCS reservoirs. We present experimental evidence that reservoirs with reducing redox conditions are favorable environments for the relatively rapid abiotic reduction of CO2 to organic molecules. In these experiments, an aqueous suspension of magnetite nanoparticles was reacted with supercritical CO2 under pressure and temperature conditions relevant to GCS in sedimentary reservoirs (95–210°C and ∼100bars of CO2). Hydrogen production was observed in several experiments, likely caused by Fe(II) oxidation either at the surface of magnetite or in the aqueous phase. Heating of the Fe(II)-rich system resulted in elevated PH2 and conditions favorable for the reduction of CO2 to acetic acid. Implications of these results for the long-term fate of CO2 in field-scale systems were explored using reaction path modeling of CO2 injection into reservoirs containing Fe(II)-bearing primary silicate minerals, with kinetic parameters for CO2 reduction obtained experimentally. The results of these calculations suggest that the reaction of CO2 with reservoir constituents will occur in two primary stages (1) equilibration of CO2 with organic acids resulting in mineral–fluid disequilibrium, and (2) gradual dissolution of primary minerals promoting significant CO2 reduction through the release of Fe(II). The reduction of CO2 is identified as a new trapping mechanism that could significantly enhance the long-term stability of GCS reservoirs. Identification of reservoir characteristics that promote CO2 redox transformations could be used as an additional factor in screening geologic reservoirs for GCS.

Hydrogeochemical study of an ophiolitic aquifer: a case study of Lago (Southern Italy, Calabria)

A hydrogeochemical survey was carried out in the area of Lago (Calabria region, Southern Italy) and outcropping geological units were classified from the hydrogeological point of view, to explain the evolution of local groundwaters. In addition, reaction path modeling was performed to simulate the evolution of groundwaters upon interaction with local metabasalts, phyllites, and serpentinites, by means of the EQ3/6 software package, version 8.0. Simulations were carried at constant temperature of 14.1 °C, which reproduces the average temperature of local groundwaters. Three different simulations have been performed for the average metabasalt fixing the fugacity of CO2 at either 10−2.4 bar (mean value), 10−2.0 bar (mean value + 1σ), or 10−2.9 bar (mean value − 1σ). The simulation for the average serpentinite and phyllite was carried out at the mean value of the fugacity of CO2 (10−2.4 bar). All evidences acquired in this study, namely the hydrogeological framework, the chemical analysis of local groundwaters and the results of reaction path modeling, consistently point out that groundwater circulation under ordinary hydraulic gradient, primarily occurs in the ophiolitic sub-complex and that dissolution of metabasalts and serpentinites controls the chemical characteristics of the groundwaters from the study area.

Coupled alkali feldspar dissolution and secondary mineral precipitation in batch systems: 5. Results of K-feldspar hydrolysis experiments

This paper explores how dissolution and precipitation reactions are coupled in batch reactor experimental systems at elevated temperatures. This is the fifth paper in our series of “Coupled Alkali Feldspar Dissolution and Secondary Mineral Precipitation in Batch Systems.” In the previous four papers we presented batch experiments of alkali-feldspar hydrolysis and explored the coupling of dissolution and precipitation reactions (Fu et al. in Chem Geol 91:955–964, 2009; Zhu and Lu in Geochim Cosmochim Acta 73:3171–3200, 2009; Zhu et al.in Geochim Cosmochim Acta 74:3963–3983, 2010; Lu et al. in Appl Geochem 30:75–90, 2013). Here, we present the results of additional K-rich feldspar hydrolysis experiments at 150 °C. Our solution chemistry measurements have constrained feldspar dissolution rates, and our high resolution transmission electron microscopy work has identified boehmite precipitation. Reaction path modeling of K-feldspar dissolution and boehmite precipitation simulated the coupled reactions, but only with forced changes of boehmite rate law in the middle of experimental duration. The results which are reported in this article lend further support to our hypothesis that slow secondary mineral precipitation explains part of the well-known apparent discrepancy between lab measured and field estimated feldspar dissolution rates (Zhu et al. in Water–rock interaction, 2004).

Clay mineral precipitation and low silica in glacier meltwaters explored through reaction-path modelling

AbstractThe subglacial chemical weathering environment is largely controlled by low temperatures and the presence of freshly comminuted minerals with a high surface area. These characteristics are believed to promote dissolution processes that give rise to low silica and high Ca2+fluxes emanating from glacierized basins. We test an alternative hypothesis, that mineral precipitation reactions in the subglacial environment play an equally important role in controlling the water chemistry in glacierized basins. We analyze borehole and proglacial water chemistry from a subarctic polythermal glacier, complemented by mineral XRD analysis of suspended sediment, till and bedrock samples. In conjunction with a thermodynamic analysis of the water and mineral chemistry, we use reaction-path modelling to study the chemical enrichment of water through the glacier system. We find that the high pH of the subglacial environment is conducive to secondary mineral precipitation, and that it is not possible to balance the water chemistry using dissolution reactions alone. We show that low silica can be explained by standard weathering reactions without having to invoke mineral-leaching reactions. Our results suggest that subglacial weathering intensity may be significantly underestimated if the production of secondary minerals is not considered.

Electron transfer within a reaction path model calibrated by constrained DFT calculations: application to mixed-valence organic compounds

The quantum dynamics of electron transfer in mixed-valence organic compounds is investigated using a reaction path model calibrated by constrained density functional theory (cDFT). Constrained DFT is used to define diabatic states relevant for describing the electron transfer, to obtain equilibrium structures for each of these states and to estimate the electronic coupling between them. The harmonic analysis at the diabatic minima yields normal modes forming the dissipative bath coupled to the electronic states. In order to decrease the system-bath coupling, an effective one dimensional vibronic Hamiltonian is constructed by partitioning the modes into a linear reaction path which connects both equilibrium positions and a set of secondary vibrational modes, coupled to this reaction coordinate. Using this vibronic model Hamiltonian, dissipative quantum dynamics is carried out using Redfield theory, based on a spectral density which is determined from the cDFT results. In a first benchmark case, the model is applied to a series of mixed-valence organic compounds formed by two 1,4-dimethoxy-3-methylphenylene fragments linked by an increasing number of phenylene bridges. This allows us to examine the coherent electron transfer in extreme situations leading to a ground adiabatic state with or without a barrier and therefore to the trapping of the charge or to an easy delocalization.

Weathering processes affecting granitoid profiles of Capo Vaticano (Calabria, southern Italy) based on petrographic, mineralogic and reaction path modelling approaches

This work focuses on developing multidisciplinary research on weathering profiles of granitoid rocks related to the tectonic and landscape evolution of the Capo Vaticano area, Calabria, southern Italy. During the Pleistocene, the Mediterranean climate plays, on the already decomposed plutonic rocks, important processes of alteration, on both the highest and inland areas and the coastal areas of the Calabrian region, such as the studied area. Field observations coupled to chemical, minero‐petrographical features and geochemical modelling are used to characterize the weathering processes affecting the granitoid complex. The granitoid cut slopes show a generally simple weathering profile characterized by a progressive increase in weathering towards the top of the slopes. The completely weathered rocks (class V) and residual soil (class VI) contain a high percentage of altered minerals, microfractures, and voids. The main mineralogical changes are the partial transformation of biotite and the partial destruction of feldspars (mainly plagioclase) that are associated with the neoformation of secondary clay minerals and ferruginous products during the most advanced stage of weathering. These transformations produce a substitution of the original rock fabric. Geochemical modelling showing the precipitation of kaolinite, illite, vermiculite, ferrihydrite and calcite. These secondary solid phases are similar to those found in this natural system. Thus, the final results of the weathering process is a soil‐like material mainly characterized by mostly a sand to gravel grain‐size fractions related to microfabric changes and mineralogical and chemical variations. Copyright © 2014 John Wiley & Sons, Ltd.

Garnets within geode-like serpentinite veins: Implications for element transport, hydrogen production and life-supporting environment formation

Geochemical micro-environments within serpentinizing systems can abiotically synthesize hydrocarbons and provide the ingredients required to support life. Observations of organic matter in microgeode-like hydrogarnets found in Mid-Atlantic Ridge serpentinites suggest these garnets possibly represent unique nests for the colonization of microbial ecosystems within the oceanic lithosphere. However, little is known about the mineralogical and geochemical processes that allow such unique environments to form. Here we present work on outcrop-scale vein networks from an ultramafic massif in Norway that contain massive amounts of spherulitic garnets (andradite), which help to constrain such processes. Vein andradite spherulites are associated with polyhedral serpentine, brucite, Ni–Fe alloy (awaruite), and magnetite indicative of low temperature (<200°C) alteration under low fO2 and low aSiO2,aq geochemical conditions. Together with the outcrop- and micro-scale analysis geochemical reaction path modeling shows that there was limited mass transport and fluid flow over a large scale. Once opened the veins remained isolated (closed system), forming non-equilibrium microenvironments that allowed, upon a threshold supersaturation, the rapid crystallization (seconds to weeks) of spherulitic andradite. The presence of polyhedral serpentine spheres indicates that veins were initially filled with a gel-like protoserpentine phase. In addition, massive Fe oxidation associated with andradite formation could have generated as much as 600mmol H2,aq per 100cm3 vein. Although no carboneous matter was detected, the vein networks fulfill the reported geochemical criteria required to generate abiogenic hydrocarbons and support microbial communities. Thus, systems similar to those investigated here are of prime interest when searching for life-supporting environments within the deep subsurface.

Detection of iron substitution in natroalunite-natrojarosite solid solutions and potential implications for Mars

Natroalunite containing substantial amounts of Fe occurs as a prominent secondary phase during acid-sulfate alteration of pyroclastic basalts in volcanic fumaroles in Nicaragua and elsewhere, and has been observed in laboratory simulations of acid-sulfate alteration as well. Reaction path models constrained by field and experimental observations predict that Fe-rich natroalunite should also form as a major secondary phase during alteration of martian basalt under similar circumstances. Here, we evaluate the potential to use spectroscopic methods to identify minerals from the alunite group with chemical compositions intermediate between natroalunite and natrojarosite on the surface of Mars, and to remotely infer their Fe contents. X-ray diffraction and spectroscopic measurements (Raman, visible/ near infrared, mid-infrared, Mössbauer) were obtained for a suite of synthetic solid solutions with a range of Fe contents ranging from natroalunite to natrojarosite. In the visible/near infrared, minerals with intermediate compositions display several spectral features not evident in end-member spectra that could be used to remotely identify these minerals and infer their composition. In addition, Raman spectra, mid-infrared spectra, and X-ray diffraction peaks all show systematic variation with changing Fe content, indicating that these methods could potentially be used to infer mineral compositions as well. The results suggest that alunite group minerals with intermediate Fe compositions may be able to account for some visible/near-infrared and Mössbauer spectral features from Mars that had previously been unidentified or attributed to other phases. Overall, our findings indicate that consideration of solid solutions may lead to new identifications of alunite group minerals on the surface of Mars, and raise the possibility that minerals with compositions intermediate between natroalunite and natrojarosite may be widely distributed on the planet.

Quantum optimal control pathways of ozone isomerization dynamics subject to competing dissociation: A two-state one-dimensional model

We construct a two-state one-dimensional reaction-path model for ozone open → cyclic isomerization dynamics. The model is based on the intrinsic reaction coordinate connecting the cyclic and open isomers with the O2 + O asymptote on the ground-state (1)A(') potential energy surface obtained with the high-level ab initio method. Using this two-state model time-dependent wave packet optimal control simulations are carried out. Two possible pathways are identified along with their respective band-limited optimal control fields; for pathway 1 the wave packet initially associated with the open isomer is first pumped into a shallow well on the excited electronic state potential curve and then driven back to the ground electronic state to form the cyclic isomer, whereas for pathway 2 the corresponding wave packet is excited directly to the primary well of the excited state potential curve. The simulations reveal that the optimal field for pathway 1 produces a final yield of nearly 100% with substantially smaller intensity than that obtained in a previous study [Y. Kurosaki, M. Artamonov, T.-S. Ho, and H. Rabitz, J. Chem. Phys. 131, 044306 (2009)] using a single-state one-dimensional model. Pathway 2, due to its strong coupling to the dissociation channel, is less effective than pathway 1. The simulations also show that nonlinear field effects due to molecular polarizability and hyperpolarizability are small for pathway 1 but could become significant for pathway 2 because much higher field intensity is involved in the latter. The results suggest that a practical control may be feasible with the aid of a few lowly excited electronic states for ozone isomerization.

Geochemical modeling of CO2–water–rock interactions for two different hydrochemical types of CO2-rich springs in Kangwon District, Korea

Naturally outflowing CO2-rich springs are a natural analogue of the seepage of sequestered CO2 in geological storage sites. In Kangwon district of South Korea, two hydrochemically different types of CO2-rich springs (i.e., Ca–HCO3-type and Na–HCO3-type) occur together in a granitic terrain. Hydrochemical and water-isotope data (i.e., δ18O–δD and tritium) show that Na–HCO3-type springs have experienced significant silicate weathering processes over a long residence time at depths, while Ca–HCO3-type springs were formed by the mixing of Na–HCO3-type springs with shallow groundwater during ascent. In this study, diverse geochemical models including mixing, ion exchange and reaction path were investigated to verify the geochemical processes accounting for the occurrence of two contrasting types of CO2-rich springs. The mixing and ion exchange models reveal that Ca–HCO3-type springs are well explained by reverse cation exchange occurring during the mixing of Na–HCO3-type springs with shallow groundwater. The Na–HCO3-type springs are well explained by the reaction path modeling including the dissolution of silicate minerals (plagioclase, K-feldspar and biotite) and the precipitation of secondary minerals (calcite, kaolinite, muscovite and Mg-beidellite), implying that dissolved carbon is sequestered by calcite precipitation (i.e., mineral trapping). However, the concentrations of K in our modeling results are far below those of K observed in Na–HCO3-type springs, because of the precipitation of muscovite considered in the model, suggesting the partial disequilibrium state of the aquifer during the hydrolysis of K-feldspar under high PCO2 conditions. This result implies that to better predict long-term CO2–water–rock interactions in a geological storage site with abundant K-feldspar, the secondary K-bearing minerals should be carefully predicted, because a target aquifer can be far from chemical equilibrium during the storage period. This study shows that geochemical modeling can be effectively used to predict the hydrochemical changes of groundwater during long-term CO2–water–rock interactions and subsequent leakage toward surface in K-feldspar rich aquifer, although it should be included in a fully coupled computational approach between fluid flow, heat transfer and reactive mass transport processes in the future research.

Characterization of granitoid profiles in the Sila Massif (Calabria, southern Italy) and reconstruction of weathering processes by mineralogy, chemistry, and reaction path modeling

This paper concerns the development of a multidisciplinary research on weathering profiles of granitoid rocks in the Sila Massif (Calabria, southern Italy), based on field investigations, chemical and minero-petrographic data, and geochemical modeling. It aims at evaluating modes and degree of weathering and focuses on the main transformation processes of the parent rock, integrating information obtained by direct observations/analyses on samples with results of simulations of pertinent water–rock interaction processes, carried out through the reaction-path-modeling approach. Physical responses to geological hammer hitting and morphological weathering features were used to characterize increasing weathering grade (I–VI weathering classes) of a representative weathering profile. Also, the main microfabric and minero-petrographic features were observed in thin sections; XRPD and SEM-EDS were used to identify primary minerals and neoformed products. Progressive dissolution of the granitoid rock was simulated using the software package EQ3/6, 8.0 and a modified version of the thermodynamic database data0.ymp.R5. A kinetic mode under closed-system conditions was applied with respect to a defined set of secondary solid phases, which are allowed to precipitate. The partial transformation of biotite and the partial destruction of feldspars, associated with the neoformation of secondary minerals and a substitution of the original rock fabric are the main mineralogical changes observed. Neoformed clay minerals and ferric products replaced feldspars and biotite during the most advanced weathering stage. Microfractures and morphological variations occur on the original rock. The final result of weathering process is a soil-like rock characterized by sand-gravel grain-size fraction. Results of geochemical modeling suggest that the chemical weathering processes occurring in the study area are relatively close to an iso-chemical transformation of the original granitoid rock, based on the small predicted changes in the concentrations of solutes from the initial to the final state of the simulation. The CO2-controlled dissolution of albite-rich plagioclase is the most important reaction, followed by the dissolution of K-feldspar, biotite, chlorite, and muscovite, in order of decreasing importance. The precipitating secondary minerals are ferrihydrite, saponite, vermiculite, illite, and kaolinite in order of decreasing pH values. The order of appearance and the quantities of secondary (product) minerals depend on the setup of geochemical modeling. Based on the standard thermodynamic properties of different illite endmembers, calculated in this work, it was possible to predict the varying compositions of the illite solid solution, which resulted to be similar to those observed in natural systems.

The chemistry and element fluxes of the July 2011 Múlakvísl and Kaldakvísl glacial floods, Iceland

This study describes the chemical composition and fluxes of two ~2000m3/s glacial floods which emerged from the Icelandic Mýrdalsjökull and Vatnajökull glaciers into the Múlakvísl and Kaldakvísl rivers in July 2011. Water samples collected during both floods had neutral to alkaline pH and conductivity from 100 to 900μS/cm. The total dissolved inorganic carbon (DIC), present mostly as HCO3−, was ~9mmol/kg during the flood peak in the Múlakvísl but stabilized at around 1mmol/kg; a similar behaviour was observed in the Kaldakvísl. Up to 1.5μmol/kg of H2S was detected. Concentrations of most of the dissolved constituents in the flood waters were comparable to those commonly observed in these rivers. In contrast, the particulate suspended material concentration increased dramatically during the floods and dominated chemical transport during these events. Waters were supersaturated with respect to a number of clays, zeolites, carbonates, and Fe hydroxides. The most soluble elements were Na, Ca, K, Sr, Mn, and Mg, whereas the least soluble were Ti, Al, and REE. This is consistent with the compositions of typical surface waters in basaltic terrains and the compositions of global rivers in general. The toxic metal concentrations were below drinking water limits, suggesting that there was no detrimental effect of flood waters chemistry on the environment. Increased concentration of DOC, formate, and acetate in the flood waters suggests substantial subglacial microbiological activity in the melt water prior to the floods. Reaction path modelling of the flood water chemical evolution suggests that it experienced subglacial water–rock interaction for at least a year in the presence of limited amounts of acid gases (e.g. SO2, HCl and HF). This suggests that the heat source for glacier melting was geothermal rather than volcanic.

Comparison of the Mineral Trapping Capacity in three Reservoirs with Variable Mineral Compositions under CO2 Saturated Conditions

Abstract The mineral trapping capacity is considered the most secure long-term CO 2 storage mechanism as it permanently demobilizes injected carbon. Here we compare three different reservoir rock mineral compositions in terms of their mineral trapping capacity using a mass balance approach. The evolution of carbon fractions in the form of residual CO2, CO 2 in the formation water and carbon stored in minerals is predicted over time using reaction path modelling. The two studied siliciclastic reservoirs (Precipice Sandstone, Surat Basin, Australia; Pretty Hill Formation, Otway Basin Australia) have no or only a very small mineral trapping capacity, whereas the volcanoclastic reservoir (Takinoue Formation, central Hokkaido, Japan) has a very large mineral trapping capacity. This difference results from the abundance of reactive Ca-, Mg- and Fe-bearing silicate minerals. It is demonstrated that the mineral trapping capacity of volcanoclastic rocks can exceed residual and solubility trapping. The limitation of the chosen approach is a rather simplistic treatment of mineral dissolution and precipitation kinetics.

Weathering of cobalt arsenides: Natural assemblages and calculated stability relations among secondary Ca-Mg-Co arsenates and carbonates

The supergene alteration of cobalt arsenides produces various characteristic mineral assemblages including erythrite, pharmacolite, and other Ca±Mg±Co-bearing arsenates, which upon precipitation remove Co and As from natural waters. Their paragenetic relationships and stability conditions have not been investigated in detail. We present a detailed study on these assemblages, their successions and coexisting fluid compositions from the mining area of Wittichen, southwest Germany, where primary skutterudite and safflorite in granite-hosted barite-calcite veins are undergoing oxidation. Water analyses from the old mines, a semi-quantitative stability diagram and quantitative reaction path modeling are used to constrain their conditions of formation. Cobalt- and arsenate-bearing solutions invariably precipitate erythrite first and hence buffer Co concentrations to very low values. Both during skutterudite or safflorite dissolution and erythrite precipitation, the fluid’s Co/As ratio decreases rapidly. Therefore, spherocobaltite (Co carbonate) is unstable in the presence of arsenate ions under most conditions. The formation of various mineral assemblages precipitating after or simultaneously with erythrite strongly depends on Ca 2+ and Mg 2+ activities and pH. Small changes in one of these parameters lead to different mineral assemblages. These small changes are partly governed by fluid-host rock or fluid-vein mineral reactions and partly by the precipitation of the secondary arsenate minerals themselves. This complex interdependence produces the rich variety of mineral assemblages observed, which effectively serves as a very sensitive monitor of fluid compositions. Furthermore, the assemblages themselves are able to buffer the Ca-Mg-Co-As concentrations in the fluid to some extent and effectively immobilize both As and Co in close proximity to the ore deposit.

Evolution of formation water chemistry and geochemical modelling of the CO2CRC Otway Site residual gas saturation test

Abstract The CO 2 CRC Otway Project Stage 2B field test was a residual CO 2 saturation and dissolution experiment carried out on the Paaratte Formation in the Otway Basin of Australia. During the 87 day test a downhole U-tube sampling assembly was used to collect formation water samples at various time intervals. The waters were analysed for chemical composition, dissolved gas content and stable isotopic composition of H and O. Changes in the chemical and isotopic composition of the formation water were observed from the initial baseline samples collected through to the conclusion of the test. Systematic reoccurrences of relatively large linear changes in the alkalinity, Ca 2+ , Fe 2+ , Mg 2+ and SiO2(aq) were observed during different test sequences. Similar behaviour occurred for the δ 18 O and δ 2 H values suggesting a complex system controlled by at least two processes. The chemical evolution was consistent with CO 2 -water-rock interactions, dominated by carbonate dissolution with some silicate dissolution. The mineral dissolution driven changes in water composition are overlain by what was clearly mixing of the injected and in situ formation water. The isotopic composition of the water was used to confirm the role of mixing and the calculated residual gas saturation values were broadly consistent with those derived by other methods. The extent of reaction in the relatively short time frame of the test was used to evaluate the capabilities of kinetics based reaction path models. The models were generated using published reaction rate data with commonly used assumptions regarding upscaling of reactive surface area. These assumptions consist of reducing the calculated geometric surface area that accounts for grain shape and roughness by factors of 100 to 1000 depending on the mineral habit. The numerical models provided a very good fit to the field data indicating that the rate data and the associated assumptions are relatively robust.