Geology topics

I.-M. Chou

Publications and source records attributed to I.-M. Chou.

At least 19 recordsLinked to original sources

USGS2022

Spectral reflectance properties (0.4-2.5 μm) of secondary Fe-oxide, Fe-hydroxide, and Fe-sulphate-hydrate minerals associated with sulphide-bearing mine wastes

Diffuse reflectance spectra of 15 mineral species commonly associated with sulphide-bearing mine wastes show diagnostic absorption bands related to electronic processes involving ferric and/or ferrous iron, and to vibrational processes involving water and hydroxyl. Many of these absorption bands are relatively broad and overlapping; however, spectral analysis methods, including continuum removal and derivative analysis, permit most of the minerals to be distinguished. Key spectral differences between the minerals are illustrated in a series of plots showing major absorption band centres and other spectral feature positions. Because secondary iron minerals are sensitive indicators of pH, Eh, relative humidity, and other environmental conditions, spectral mapping of mineral distributions promises to have important application to mine waste remediation studies.

Geochemistry: Exploration, Environment, Analysis↗

USGS2013

Determination of diffusion coefficients of carbon dioxide in water between 268 and 473 K in a high-pressure capillary optical cell with in situ Raman spectroscopic measurements

Accurate values of diffusion coefficients for carbon dioxide in water and brine at reservoir conditions are essential to our understanding of transport behavior of carbon dioxide in subsurface pore space. However, the experimental data are limited to conditions at low temperatures and pressures. In this study, diffusive transfer of carbon dioxide in water at pressures up to 45 MPa and temperatures from 268 to 473 K was observed within an optical capillary cell via time-dependent Raman spectroscopy. Diffusion coefficients were estimated by the least-squares method for the measured variations in carbon dioxide concentration in the cell at various sample positions and time. At the constant pressure of 20 MPa, the measured diffusion coefficients of carbon dioxide in water increase with increasing temperature from 268 to 473 K. The relationship between diffusion coefficient of carbon dioxide in water [D(CO 2 ) in m 2 /s] and temperature (T in K) was derived with Speedy–Angell power-law approach as: D(CO 2 )=D 0 [T/Ts-1] m where D 0 = 13.942 × 10 −9 m 2 /s, Ts = 227.0 K, and m = 1.7094. At constant temperature, diffusion coefficients of carbon dioxide in water decrease with pressure increase. However, this pressure effect is rather small (within a few percent).

Geochimica et Cosmochimica Acta↗

USGS2011

Stability of Mg-sulfates at-10C and the rates of dehydration/rehydration processes under conditions relevant to Mars

We report the results of low temperature (−10°C) experiments on the stability fields and phase transition pathways of five hydrous Mg-sulfates. A low temperature form of MgSO 4 ·7H 2 O (LT-7w) was found to have a wide stability field that extends to low relative humidity (∼13% RH at −10°C). Using information on the timing of phase transitions, we extracted information on the reaction rates of five important dehydration and rehydration processes. We found that the temperature dependencies of rate constants for dehydration processes differ from those of rehydration, which reflect differences in reaction mechanisms. By extrapolating these rate constants versus T correlations into the T range relevant to Mars, we can evaluate the possibility of occurrence of specific processes and the presence of common Mg-sulfate species present on Mars in different periods and locations. We anticipate in a moderate obliquity period, starkeyite and LH-MgSO 4 ·H 2 O should be two common Mg-sulfates at the surface, another polymorph MH-MgSO 4 ·H 2 O can exist at the locations where hydrothermal processes may have occurred. In polar regions or within the subsurface of other regions, meridianiite (coexisting with water ice, near 100% RH) and LT-7w (over a large RH range) are the stable phases. During a high obliquity period, meridianiite and LT-7w should exhibit widespread occurrence. The correlations of reaction rates versus temperature found in this study imply that dehydration and rehydration of hydrous Mg-sulfates would always be slower than the sublimation and crystallization of water ice, which would be supported by mission observations from Odyssey and by Mars Exploration Rovers.

Journal of Geophysical Research E: Planets↗

USGS2011

Experimental determination of the phase boundary between kornelite and pentahydrated ferric sulfate at 0.1MPa

Recent findings of various ferric sulfates on Mars emphasize the importance of understanding the fundamental properties of ferric sulfates at temperatures relevant to that of Martian surface. In this study, the phase boundary between kornelite (Fe2(SO4)3.7H2O) and pentahydrated ferric sulfate (Fe2(SO4)3.5H2O) was experimentally determined using the humidity-buffer technique together with gravimetric measurements and Raman spectroscopy at 0.1MPa in the 36-56??C temperature range. Through the thermodynamic analysis of our experimental data, the enthalpy change (-290.8??0.3kJ/mol) and the Gibbs free energy change (-238.82??0.02kJ/mol) for each water molecule of crystallization in the rehydration of pentahydrated ferric sulfate to kornelite were obtained. ?? 2011 Elsevier B.V.

Chemical Geology↗

USGS2010

Pressure calibrants in the hydrothermal diamond-anvil cell

Based on the equation of state of water (EOSW), experimental pressure in the hydrothermal diamond-anvil cell (HDAC) using pure water or dilute aqueous solutions as a pressure medium can be accurately determined at each measured temperature. Consequently, meaningful interpretations can be obtained for observations in the HDAC, which has been widely accepted as a versatile, modern apparatus for hydrothermal experiments. However, this is not true when other pressure media were used because there is no reliable way to determine experimental pressure other than the use of in situ pressure sensors. Most of the available pressure sensors are difficult to apply because they either require expensive facilities to perform the measurements or are unable to provide the accuracy needed for the interpretation of hydrothermal experiments. The only exception is to use the interferometric method to detect the ??-?? quartz transition, although such applications are limited to temperatures above 573??C. In this study, three pressure calibrants were calibrated for applications at lower temperatures, and they were based on visual observation of the ferroelastic phase transitions in BaTiO3 (tetragonal/cubic), Pb3(PO4)2 (monoclinic/trigonal), and PbTiO3 (tetragonal/cubic). For the phase transitions in BaTiO3 and Pb3(PO4)2, the temperature at which twinning disappears during heating was taken as the transition temperature (Ttr); the phase transition pressures (Ptr) can be calculated, respectively, from Ptr (MPa; ??3%) = 0.17 - 21.25 [(Ttr) - 115.3], and Ptr (MPa; ??2%) = 1.00 - 10.62 [(Ttr) - 180.2], where Ttr is in ??C. For the phase transition in PbTiO3, the temperature at which the movement of phase front begins (or ends) on heating (or cooling) was taken as the transition temperature (Ttr,h or Ttr,c), and the phase transition pressures on heating (Ptr,h) and cooling (Ptr,c) can be calculated from Ptr,h (MPa; ??4%) = 7021.7 - 14.235 (Ttr,h), and Ptr,c (MPa; ??4%) = 6831.3 - 14.001 (Ttr,c). Phase transitions for these three pressure calibrants are easy to detect visually, and their P-T phase boundaries have negative slopes and intersect isochors of most of the geologic fluids at high angles and, therefore, are easy to apply. Copyright ?? 2007 by V. H. Winston & Son, Inc. All rights reserved.

International Geology Review↗

USGS2009

Producing fired bricks using coal slag from a gasification plant in indiana

Integrated gasification combined cycle (IGCC) is a promising power generation technology which increases the efficiency of coal-to-power conversion and enhances carbon dioxide concentration in exhaust emissions for better greenhouse gas capture. Two major byproducts from IGCC plants are bottom slag and sulfur. The sulfur can be processed into commercially viable products, but high value applications need to be developed for the slag material in order to improve economics of the process. The purpose of this study was to evaluate the technical feasibility of incorporating coal slag generated by the Wabash River IGCC plant in Indiana as a raw material for the production of fired bricks. Full-size bricks containing up to 20 wt% of the coal slag were successfully produced at a bench-scale facility. These bricks have color and texture similar to those of regular fired bricks and their water absorption properties met the ASTM specifications for a severe weathering grade. Other engineering properties tests, including compressive strength tests, are in progress.

Conference Paper↗

USGS2008

In situ Raman spectroscopic investigation of the structure of subduction-zone fluids

In situ Raman spectra of synthetic subduction-zone fluids (KAlSi3O8-H2O system) were measured to 900?? and 2.3 GPa using a hydrothermal diamond-anvil cell. The structures of aqueous fluid and hydrous melt become closer when conditions approach the second critical endpoint. Almost no three-dimensional network was observed in the supercritical fluid above 2 GPa although a large amount of silicate component is dissolved, suggesting that the physical and chemical properties of these phases change drastically at around the second critical endpoint. Our experimental results indicate that the fluids released from a subducting slab change from aqueous fluid to supercritical fluid with increasing depth under the volcanic arcs. Copyright 2008 by the American Geophysical Union.

Journal of Geophysical Research B: Solid Earth↗

USGS2008

Determination of methane concentrations in water in equilibrium with sI methane hydrate in the absence of a vapor phase by in situ Raman spectroscopy

Most submarine gas hydrates are located within the two-phase equilibrium region of hydrate and interstitial water with pressures (P) ranging from 8 to 60 MPa and temperatures (T) from 275 to 293 K. However, current measurements of solubilities of methane in equilibrium with hydrate in the absence of a vapor phase are limited below 20 MPa and 283.15 K, and the differences among these data are up to 30%. When these data were extrapolated to other P-T conditions, it leads to large and poorly known uncertainties. In this study, in situ Raman spectroscopy was used to measure methane concentrations in pure water in equilibrium with sI (structure one) methane hydrate, in the absence of a vapor phase, at temperatures from 276.6 to 294.6 (??0.3) K and pressures at 10, 20, 30 and 40 (??0.4%) MPa. The relationship among concentration of methane in water in equilibrium with hydrate, in mole fraction [X(CH4)], the temperature in K, and pressure in MPa was derived as: X(CH4) = exp [11.0464 + 0.023267 P - (4886.0 + 8.0158 P)/T]. Both the standard enthalpy and entropy of hydrate dissolution at the studied T-P conditions increase slightly with increasing pressure, ranging from 41.29 to 43.29 kJ/mol and from 0.1272 to 0.1330 kJ/K ?? mol, respectively. When compared with traditional sampling and analytical methods, the advantages of our method include: (1) the use of in situ Raman signals for methane concentration measurements eliminates possible uncertainty caused by sampling and ex situ analysis, (2) it is simple and efficient, and (3) high-pressure data can be obtained safely. ?? 2007 Elsevier Ltd. All rights reserved.

Geochimica et Cosmochimica Acta↗

USGS2007

Synchrotron x-ray spectroscopy of EuHN O3 aqueous solutions at high temperatures and pressures and Nb-bearing silicate melt phases coexisting with hydrothermal fluids using a modified hydrothermal diamond anvil cell and rail assembly

A modified hydrothermal diamond anvil cell (HDAC) rail assembly has been constructed for making synchrotron x-ray absorption spectroscopy, x-ray fluorescence, and x-ray mapping measurements on fluids or solid phases in contact with hydrothermal fluids up to ???900??C and 700 MPa. The diamond anvils of the HDAC are modified by laser milling grooves or holes, for the reduction of attenuation of incident and fluorescent x rays and sample cavities. The modified HDAC rail assembly has flexibility in design for measurement of light elements at low concentrations or heavy elements at trace levels in the sample and the capability to probe minute individual phases of a multiphase fluid-based system using focused x-ray microbeam. The supporting rail allows for uniform translation of the HDAC, rotation and tilt stages, and a focusing mirror, which is used to illuminate the sample for visual observation using a microscope, relative to the direction of the incident x-ray beam. A structure study of Eu(III) aqua ion behavior in high-temperature aqueous solutions and a study of Nb partitioning and coordination in a silicate melt in contact with a hydrothermal fluid are described as applications utilizing the modified HDAC rail assembly. ?? 2007 American Institute of Physics.

Review of Scientific Instruments↗

USGS2007

On the formation and structure of rare-earth element complexes in aqueous solutions under hydrothermal conditions with new data on gadolinium aqua and chloro complexes

Synchrotron X-ray spectroscopy experiments were made on the Gd(III) aqua and chloro complexes in low pH aqueous solutions at temperatures ranging from 25 to 500????C and at pressures up to 480??MPa using a hydrothermal diamond anvil cell. Analysis of fluorescence Gd L3-edge X-ray absorption fine structure (XAFS) spectra measured from a 0.006m Gd/0.16m HNO3 aqueous solution at temperatures up to 500????C and at pressures up to 260??MPa shows that the Gd-O distance of the Gd3+ aqua ion decreases steadily at a rate of ??? 0.007??A??/100????C whereas the number of coordinated H2O molecules decreases from 9.0 ?? 0.5 to 7.0 ?? 0.4. The loss of water molecules in the Gd3+ aqua ion inner hydration shell over this temperature range (a 22% reduction) is smaller than exhibited by the Yb3+ aqua ion (42% reduction) indicating that the former is significantly more stable than the later. We conjecture that the anomalous enrichment of Gd reported from measurement of REE concentrations in ocean waters may be attributed to the enhanced stability of the Gd3+ aqua ion relative to other REEs. Gd L3-edge XAFS measurements of 0.006m and 0.1m GdCl3 aqueous solutions at temperatures up to 500????C and pressures up to 480??MPa reveal that the onset of significant Gd3+-Cl- association occurs around 300????C. Partially-hydrated stepwise inner-sphere complexes most likely of the type Gd(H2O)??-nCln+3-n occur in the chloride solutions at higher temperatures, where ?? ??? 8 at 300????C decreasing slightly to an intermediate value between 7 and 8 upon approaching 500????C. This is the first direct evidence for the occurrence of partially-hydrated REE Gd (this study) and Yb [Mayanovic, R.A., Jayanetti, S., Anderson, A.J., Bassett, W.A., Chou, I-M., 2002a. The structure of Yb3+ aquo ion and chloro complexes in aqueous solutions at up to 500 ??C and 270 MPa. J. Phys. Chem. A 106, 6591-6599.] chloro complexes in hydrothermal solutions. The number of chlorides (n) of the partially-hydrated Gd(III) chloro complexes increases steadily with temperature from 0.4 ?? 0.2 to 1.7 ?? 0.3 in the 0.006m chloride solution and from 0.9 ?? 0.7 to 1.8 ?? 0.7 in the 0.1m GdCl3 aqueous solution in the 300-500????C range. Conversely, the number of H2O ligands of Gd(H2O)??-nCln+3-n complexes decreases steadily from 8.9 ?? 0.4 to 5.8 ?? 0.7 in the 0.006m GdCl3 aqueous solution and from 9.0 ?? 0.5 to 5.3 ?? 1.0 in the 0.1m GdCl3 aqueous solution at temperatures from 25 to 500????C. Analysis of our results shows that the chloride ions partially displace the inner-shell water molecules during Gd(III) complex formation under hydrothermal conditions. The Gd-OH2 bond of the partially-hydrated Gd(III) chloro complexes exhibits slightly smaller rates of length contraction (??? 0.005??A??/100????C) for both solutions. The structural aspects of chloride speciation of Gd(III) as measured from this study and of Yb(III) as measured from our previous experiments are consistent with the solubility of these and other REE in deep-sea hydrothermal fluids. ?? 2006 Elsevier B.V. All rights reserved.

Chemical Geology↗

USGS2007

PVTx properties of the CO 2 -H 2 O and CO 2 -H 2 O-NaCl systems below 647 K: assessment of experimental data and thermodynamic models

Evaluation of CO 2 sequestration in formation brine or in seawater needs highly accurate experimental data or models of pressure–volume–temperature-composition ( PVTx ) properties for the CO 2 –H 2 O and CO 2 –H 2 O–NaCl systems. This paper presents a comprehensive review of the experimental PVTx properties and the thermodynamic models of these two systems. The following conclusions are drawn from the review: (1) About two-thirds of experimental data are consistent with each other, where the uncertainty in liquid volumes is within 0.5%, and that in gas volumes within 2%. However, this accuracy is not sufficient for assessing CO 2 sequestration. Among the data sets for liquids, only a few are available for accurate modeling of CO 2 sequestration. These data have an error of about 0.1% on average, roughly covering from 273 to 642 K and from 1 to 35 MPa; (2) There is a shortage of volumetric data of saturated vapor phase. (3) There are only a few data sets for the ternary liquids, and they are inconsistent with each other, where only a couple of data sets can be used to test a predictive density model for CO 2 sequestration; (4) Although there are a few models with accuracy close to that of experiments, none of them is accurate enough for CO 2 sequestration modeling, which normally needs an accuracy of density better than 0.1%. Some calculations are made available on www.geochem-model.org .

Chemical Geology↗

USGS2006

In situ study of mass transfer in aqueous solutions under high pressures via Raman spectroscopy: A new method for the determination of diffusion coefficients of methane in water near hydrate formation conditions

A new method was developed for in situ study of the diffusive transfer of methane in aqueous solution under high pressures near hydrate formation conditions within an optical capillary cell. Time-dependent Raman spectra of the solution at several different spots along the one-dimensional diffusion path were collected and thus the varying composition profile of the solution was monitored. Diffusion coefficients were estimated by the least squares method based on the variations in methane concentration data in space and time in the cell. The measured diffusion coefficients of methane in water at the liquid (L)-vapor (V) stable region and L-V metastable region are close to previously reported values determined at lower pressure and similar temperature. This in situ monitoring method was demonstrated to be suitable for the study of mass transfer in aqueous solution under high pressure and at various temperature conditions and will be applied to the study of nucleation and dissolution kinetics of methane hydrate in a hydrate-water system where the interaction of methane and water would be more complicated than that presented here for the L-V metastable condition. ?? 2006 Society for Applied Spectroscopy.

Applied Spectroscopy↗

USGS2006

An improved model for the calculation of CO2 solubility in aqueous solutions containing Na+, K+, Ca2+, Mg2+, Cl-, and SO42-

An improved model is presented for the calculation of the solubility of carbon dioxide in aqueous solutions containing Na+, K+, Ca2+, Mg2+, Cl-, and SO42- in a wide temperature-pressure-ionic strength range (from 273 to 533 K, from 0 to 2000 bar, and from 0 to 4.5 molality of salts) with experimental accuracy. The improvements over the previous model [Duan, Z. and Sun, R., 2003. An improved model calculating CO2 solubility in pure water and aqueous NaCl solutions from 273 to 533K and from 0 to 2000 bar. Chemical Geology, 193: 257-271] include: (1) By developing a non-iterative equation to replace the original equation of state in the calculation of CO 2 fugacity coefficients, the new model is at least twenty times computationally faster and can be easily adapted to numerical reaction-flow simulator for such applications as CO2 sequestration and (2) By fitting to the new solubility data, the new model improved the accuracy below 288 K from 6% to about 3% of uncertainty but still retains the high accuracy of the original model above 288 K. We comprehensively evaluate all experimental CO2 solubility data. Compared with these data, this model not only reproduces all the reliable data used for the parameterization but also predicts the data that were not used in the parameterization. In order to facilitate the application to CO2 sequestration, we also predicted CO2 solubility in seawater at two-phase coexistence (vapor-liquid or liquid-liquid) and at three-phase coexistence (CO2 hydrate-liquid water-vapor CO2 [or liquid CO2]). The improved model is programmed and can be downloaded from the website http://www.geochem-model.org/programs.htm. ?? 2005 Elsevier B.V. All rights reserved.

Marine Chemistry↗

USGS2005

Determination of goslarite-bianchite equilibria by the humidity-buffer technique at 0.1 MPa

Goslarite-bianchite equilibria were determined along four humidity-buffer curves at 0.1 MPa and between 27 and 36 ??C. Results, based on tight reversals along each humidity buffer, can be represented by ln K (??0.005)=19.643-7015.38/T, where K is the equilibrium constant and T is temperature in K. Our data are in excellent agreement with several previous vapor-pressure measurements and are consistent with the solubility data reported in the literature. Thermodynamic analysis of these data yields 9.634 (??0.056) kJ mol-1 for the standard Gibbs free energy of reaction, which is in good agreement with the value of 9.658 kJ mol-1 calculated from the thermodynamic data compiled and evaluated by Wagman et al. [Wagman, D.D., Evans, W.H., Parker, V.B., Schumm, R.H., Halow. I., Bailey, S.M., Churney, K.L., Nuttal, R.L., 1982. The NBS tables of chemical thermodynamic properties. Selected values for inorganic and C1 and C2 organic substances in SI units. J. Phys. Chem. Ref. Data 11, Suppl. 2].

Chemical Geology↗

USGS2005

Producing ammonium sulfate from flue gas desulfurization by-products

Emission control technologies using flue gas desulfurization (FGD) have been widely adopted by utilities burning high-sulfur fuels. However, these technologies require additional equipment, greater operating expenses, and increased costs for landfill disposal of the solid by-products produced. The financial burdens would be reduced if successful high-volume commercial applications of the FGD solid by-products were developed. In this study, the technical feasibility of producing ammonium sulfate from FGD residues by allowing it to react with ammonium carbonate in an aqueous solution was preliminarily assessed. Reaction temperatures of 60, 70, and 80??C and residence times of 4 and 6 hours were tested to determine the optimal conversion condition and final product evaluations. High yields (up to 83%) of ammonium sulfate with up to 99% purity were achieved under relatively mild conditions. The optimal conversion condition was observed at 60??C and a 4-hour residence time. The results of this study indicate the technical feasibility of producing ammonium sulfate fertilizer from an FGD by-product. Copyright ?? Taylor & Francis Inc.

Energy Sources↗

USGS2005

Acquisition and evaluation of thermodynamic data for bieberite-moorhouseite equilibria at 0.1 MPa

Published estimates for the equilibrium relative humidity (RH) at 25 deg;C for the reaction: bieberite (CoSO4??7H2O) = moorhouseite (CoSO4??6H2O) + H2O, range from 69.8 to 74.5%. To evaluate these data, the humidity-buffer technique was used to determine equilibrium constants for this reaction between 14 and 43 ??C at 0.1 MPa. Reversals along five humidity-buffer curves yield In K = 18.03-6509.43/T, where K is the equilibrium constant, and T is temperature in K. The derived standard Gibbs free energy of reaction is 9.43 kJ/mol, which agrees well with several previously reported values based on vapor-pressure measurements. It also agrees well with values calculated from the data derived mostly from calorimetric measurements. Previous studies indicated that the temperature of the invariant point for the assemblage bieberite-moorhouseite-aqueous solution-vapor is near 44.7 ??C, and our extrapolated data predict 91.1% RH at this temperature; the predicted position for the invariant point is in excellent agreement with those reported previously.

American Mineralogist↗

USGS2003

Relaxation of the structure of simple metal ion complexes in aqueous solutions at up to supercritical conditions

Recently x-ray absorption fine structure (XAFS) studies of various ions in aqueous solutions showed a variation of cation-ligand bond lengths, often coupled with other structure changes, with increasing temperatures. Thus, the variations of the structure of several metal ion complexes with temperature based on observations from the X-ray absorption fine structure (XAFS) studies in the hope that it will stimulate the development of either first- principles theory or molecular dynamics simulations that might adequately describes these results are discussed.

Journal of Chemical Physics↗

USGS2003

Determination of epsomite-hexahydrite equilibria by the humidity-buffer technique at 0.1 MPa with implications for phase equilibria in the system MgSO4-H2O

Epsomite (MgSO 4 ·7H 2 O) and hexahydrite (MgSO 4 ·6H 2 O) are common minerals found in marine evaporite deposits, in saline lakes as precipitates, in weathering zones of coal and metallic deposits, in some soils and their efflorescences, and possibly on the surface of Europa as evaporite deposits. Thermodynamic properties of these two minerals reported in the literature are in poor agreement. In this study, epsomite-hexahydrite equilibria were determined along four humidity-buffer curves at 0.1 MPa and between 25 and 45°C. Results obtained for the reaction epsomite = hexahydrite + H 2 O, as demonstrated by very tight reversals along each humidity buffer, can be represented by ln K (± 0.012) = 20.001 - 7182.07/ T , where K is the equilibrium constant, and T is temperature in Kelvin. The derived standard Gibbs free energy of reaction is 10.13 ± 0.07 kJ/mol, which is essentially the same value as that calculated from vapor pressure measurements reported in the literature. However, this value is at least 0.8 kJ/mol lower than those calculated from the data derived mostly from calorimetric measurements.

Astrobiology↗