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Importance of mineralogical data for groundwater quality affectedby CO2 leakage

Description: Recently, geological storage of CO{sub 2} has been extensively investigated. The impact of leakage from CO{sub 2} storage reservoirs on groundwater quality is one of the concerns. Dissolution of CO{sub 2} in groundwater results in a decrease in pH. Such acidic condition can affect the dissolution and sorption mechanisms of many minerals (Jaffe and Wang, 2004). Some heavy-metal-bearing minerals dissolve under acidic conditions. For example, galena (PbS) can dissolve and increase significantly Pb concentrations and diminish groundwater quality. If calcite is present in the rock, it can buffer the pH and decrease galena dissolution. Therefore, mineralogical composition and distribution in caprock, overlying aquifers, and along the leakage paths are important data that should be obtained from site characterization. Insight into which minerals and compounds are most important for groundwater quality can be obtained from reactive geochemical transport simulations. Here we present results of simulations using the code TOUGHREACT, whose physical and chemical process capabilities have been discussed by Xu et al. (2006). The simulator can be applied to one-, two-, or three-dimensional porous and fractured media with physical and chemical heterogeneity, and can accommodate any number of chemical species present in liquid, gas and solid phases.
Date: February 13, 2006
Creator: Xu, Tianfu
Partner: UNT Libraries Government Documents Department

Zinc surface complexes on birnessite: A density functional theory study

Description: Biogeochemical cycling of zinc is strongly influenced by sorption on birnessite minerals (layer-type MnO2), which are found in diverse terrestrial and aquatic environments. Zinc has been observed to form both tetrahedral (Zn{sup IV}) and octahedral (Zn{sup VI}) triple-corner-sharing surface complexes (TCS) at Mn(IV) vacancy sites in hexagonal birnessite. The octahedral complex is expected to be similar to that of Zn in the Mn oxide mineral, chalcophanite (ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O), but the reason for the occurrence of the four-coordinate Zn surface species remains unclear. We address this issue computationally using spin-polarized Density Functional Theory (DFT) to examine the Zn{sub IV}-TCS and Zn{sup VI}-TCS species. Structural parameters obtained by DFT geometry optimization were in excellent agreement with available experimental data on Zn-birnessites. Total energy, magnetic moments, and electron-overlap populations obtained by DFT for isolated Zn{sup IV}-TCS revealed that this species is stable in birnessite without a need for Mn(III) substitution in the octahedral sheet and that it is more effective in reducing undersaturation of surface O at a Mn vacancy than is Zn{sub VI}-TCS. Comparison between geometry-optimized ZnMn{sub 3}O{sub 7} {center_dot} 3H{sub 2}O (chalcophanite) and the hypothetical monohydrate mineral, ZnMn{sub 3}O{sub 7} {center_dot} H{sub 2}O, which contains only tetrahedral Zn, showed that the hydration state of Zn significantly affects birnessite structural stability. Finally, our study also revealed that, relative to their positions in an ideal vacancy-free MnO{sub 2}, Mn nearest to Zn in a TCS surface complex move toward the vacancy by 0.08-0.11 {angstrom}, while surface O bordering the vacancy move away from it by 0.16-0.21 {angstrom}, in agreement with recent X-ray absorption spectroscopic analyses.
Date: January 5, 2009
Creator: Kwon, Kideok D.; Refson, Keith & Sposito, Garrison
Partner: UNT Libraries Government Documents Department

Stability of uranium incorporated into Fe(hydr)oxides under fluctuating redox conditions

Description: Reaction pathways resulting in uranium bearing solids that are stable (i.e., having limited solubility) under both aerobic and anaerobic conditions will limit dissolved concentrations and migration of this toxin. Here we examine the sorption mechanism and propensity for release of uranium reacted with Fe (hydr)oxides under cyclic oxidizing and reducing conditions. Upon reaction of ferrihydrite with Fe(II) under conditions where aqueous Ca-UO{sub 2}-CO{sub 3} species predominate (3 mM Ca and 3.8 mM CO{sub 3}-total), dissolved uranium concentrations decrease from 0.16 mM to below detection limit (BDL) after 5 to 15 d, depending on the Fe(II) concentration. In systems undergoing 3 successive redox cycles (15 d of reduction followed by 5 d of oxidation) and a pulsed decrease to 0.15 mM CO{sub 3}-total, dissolved uranium concentrations varied depending on the Fe(II) concentration during the initial and subsequent reduction phases - U concentrations resulting during the oxic 'rebound' varied inversely with the Fe(II) concentration during the reduction cycle. Uranium removed from solution remains in the oxidized form and is found both adsorbed on and incorporated into the structure of newly formed goethite and magnetite. Our 15 results reveal that the fate of uranium is dependent on anaerobic/aerobic conditions, aqueous uranium speciation, and the fate of iron.
Date: April 1, 2009
Creator: Stewart, B.D.; Nico, P.S. & Fendorf, S.
Partner: UNT Libraries Government Documents Department

Insight from simulations of single-well injection-withdrawal tracer tests on simple and complex fractures

Description: The single-well injection withdrawal (SWIW) test, a tracer test utilizing only one well, is proposed as a useful contribution to site characterization of fractured rock, as well as providing parameters relevant to tracer diffusion and sorption. The usual conceptual model of flow and solute transport through fractured rock with low matrix permeability involves solute advection and dispersion through a fracture network coupled with diffusion and sorption into the surrounding rock matrix. Unlike two-well tracer tests, results of SWIW tests are ideally independent of advective heterogeneity, channeling and flow dimension, and, instead, focus on diffusive and sorptive characteristics of tracer (solute) transport. Thus, they can be used specifically to study such characteristics and evaluate the diffusive parameters associated with tracer transport through fractured media. We conduct simulations of SWIW tests on simple and complex fracture models, the latter being defined as having two subfractures with altered rock blocks in between and gouge material in their apertures. Using parameters from the Aspo site in Sweden, we calculate and study SWIW tracer breakthrough curves (BTCs) from a test involving four days of injection and then withdrawal. By examining the peak concentration C{sub pk} of the SWIW BTCs for a variety of parameters, we confirm that C{sub pk} is largely insensitive to the fracture advective flow properties, in particular to permeability heterogeneity over the fracture plane or to subdividing the flow into two subfractures in the third dimension orthogonal to the fracture plane. The peak arrival time t{sub pk} is not a function of fracture or rock properties, but is controlled by the time schedule of the SWIW test. The study shows that the SWIW test is useful for the study of tracer diffusion-sorption processes, including the effect of the so-called flow-wetted surface (FWS) of the fracture. Calculations with schematic models with different FWS ...
Date: August 6, 2009
Creator: Tsang, C.-F. & Doughty, C.
Partner: UNT Libraries Government Documents Department

An asixymmetric diffusion experiment for the determination of diffusion and sorption coefficients of rock samples

Description: Diffusion anisotropy is a critical property in predicting migration of substances in sedimentary formations with very low permeability. The diffusion anisotropy of sedimentary rocks has been evaluated mainly from laboratory diffusion experiments, in which the directional diffusivities are separately estimated by through-diffusion experiments using different rock samples, or concurrently by in-diffusion experiments in which only the tracer profile in a rock block is measured. To estimate the diffusion anisotropy from a single rock sample, this study proposes an axisymmetric diffusion test, in which tracer diffuses between a cylindrical rock sample and a surrounding solution reservoir. The tracer diffusion between the sample and reservoir can be monitored from the reservoir tracer concentrations, and the tracer profile could also be obtained after dismantling the sample. Semi-analytical solutions are derived for tracer concentrations in both the reservoir and sample, accounting for an anisotropic diffusion tensor of rank two as well as the dilution effects from sampling and replacement of reservoir solution. The transient and steady-state analyses were examined experimentally and numerically for different experimental configurations, but without the need for tracer profiling. These experimental configurations are tested for in- and out-diffusion experiments using Koetoi and Wakkanai mudstones and Shirahama sandstone, and are scrutinized by a numerical approach to identify favorable conditions for parameter estimation. The analysis reveals the difficulty in estimating diffusion anisotropy; test configurations are proposed for enhanced identifiability of diffusion anisotropy. Moreover, it is demonstrated that the axisymmetric diffusion test is efficient in obtaining the sorption parameter from both steady-state and transient data, and in determining the effective diffusion coefficient if isotropic diffusion is assumed. Moreover, measuring reservoir concentrations in an axisymmetric diffusion experiment coupled with tracer profiling may be a promising approach to estimate of diffusion anisotropy of sedimentary rocks.
Date: February 1, 2011
Creator: Takeda, M.; Hiratsuka, T.; Ito, K. & Finsterle, S.
Partner: UNT Libraries Government Documents Department

Treatment of Produced Waters Using a Surfactant Modified Zeolite/Vapor Phase Bioreactor System

Description: This report summarizes work of this project from October 2003 through March 2004. The major focus of the research was to further investigate BTEX removal from produced water, to quantify metal ion removal from produced water, and to evaluate a lab-scale vapor phase bioreactor (VPB) for BTEX destruction in off-gases produced during SMZ regeneration. Batch equilibrium sorption studies were conducted to evaluate the effect of semi-volatile organic compounds commonly found in produced water on the sorption of benzene, toluene, ethylbenzene, and xylene (BTEX) onto surfactant-modified zeolite (SMZ) and to examine selected metal ion sorption onto SMZ. The sorption of polar semi-volatile organic compounds and metals commonly found in produced water onto SMZ was also investigated. Batch experiments were performed in a synthetic saline solution that mimicked water from a produced water collection facility in Wyoming. Results indicated that increasing concentrations of semi-volatile organic compounds increased BTEX sorption. The sorption of phenol compounds could be described by linear isotherms, but the linear partitioning coefficients decreased with increasing pH, especially above the pKa's of the compounds. Linear correlations relating partitioning coefficients of phenol compounds with their respective solubilities and octanol-water partitioning coefficients were developed for data collected at pH 7.2. The sorption of chromate, selenate, and barium in synthetic produced water were also described by Langmuir isotherms. Experiments conducted with a lab-scale vapor phase bioreactor (VPB) packed with foam indicated that this system could achieve high BTEX removal efficiencies once the nutrient delivery system was optimized. The xylene isomers and benzene were found to require the greatest biofilter bed depth for removal. This result suggested that these VOCs would ultimately control the size of the biofilter required for the produced water application. The biofilter recovered rapidly from shutdowns showing that the system was resilient to discontinuous feed conditions therefore provided flexibility on ...
Date: March 11, 2004
Creator: Katz, Lynn E.; Kinney, Kerry A.; Bowman, R. S. & Sullivan, E. J.
Partner: UNT Libraries Government Documents Department

Effects of Resin Particle Size and Solution Temperature on SuperLig(R) 644 Resin Performance with AN-105 Simulate

Description: The performance of the SuperLig(R) 644 resin loading and elution was evaluated at 25, 35, and 45 degree C using a single-column containing 2.25 g of oven-dry, hydrogen form of SuperLig(R) 664 resin. A simulated Envelope A solution was used to mimic the composition of low-activity waste solution from Tank 241-AN-105 supernate in the Hanford Site waste tank. The simulant was spiked with small quantities of trace metals (cadmium, chromium, iron, and lead) to evaluate the effects of these metals on cesium sorption. The results from column tests performed at 25, 35, and 45 degree C showed that more than 100 BVs of simulated Envelope A solution could be processed at each temperature before 50 percent breakthrough of the cesium occurred.
Date: July 15, 2003
Creator: Nash, C.A.
Partner: UNT Libraries Government Documents Department

Modeling of cation binding in hydrated 2:1 clay minerals. Progress report, September 15, 1996--September 14, 1997

Description: 'The primary focus of the research is the development of molecular theories of ion binding to clay minerals, with a view toward understanding the mechanism of radionuclide transport through soils. The overall aim of the research and the computational methods employed are essentially unchanged from those originally proposed. The research is split conceptually into three phases, based on the radionuclides considered. The first, cesium phase has an estimated completion time of 1.5 years from the project initiation. This phase is ongoing at this time. The second, strontium and third, uranium phases will be addressed in the second half of the project period. Phase 1 Accomplishments Code Development: A computer simulation code for the treatment of hydrated smectite and vermiculite clays with varying water content has been developed. This version of the code enables calculations under conditions of constant interlayer spacing or constant applied pressure, and for the complete series of interlayer alkali-metal ions. Final development of the code for (i), calculations of exchange free energies, and (ii), calculations at constant water chemical potential should be completed within the next month. This will allow the most important scientific issues of phase 1 to be fully addressed. Hydrated Clay Structure: The molecular structures of Cs{sup +}- and Na{sup +}-montmorillonite (a common swelling clay) have been investigated. The observed layer spacings versus water content of both clays agree well with experimental swelling curves. 1,2 This has provided validation of the simulation models. Comparison of cesium and sodium structures indicate that cesium preferentially forms inner-sphere complexes with the clay surface. The relationship of this structural observation to Na{sup +} Cs{sup +} exchange thermodynamics is presently under investigation. Dry Cs{sup +}-Montmorillonite Structure: It is thought that dry, cesium-substituted montmorillonites exist as mixed-layer structures with both symmetrical (hexagonal cavities overlapping) and non-symmetrical (hexagonal cavities shifted) stacking ...
Date: January 1, 1997
Creator: Smith, D.E.
Partner: UNT Libraries Government Documents Department

Numerical simulation of in situ bioremediation

Description: Models that couple subsurface flow and transport with microbial processes are an important tool for assessing the effectiveness of bioremediation in field applications. A numerical algorithm is described that differs from previous in situ bioremediation models in that it includes: both vadose and groundwater zones, unsteady air and water flow, limited nutrients and airborne nutrients, toxicity, cometabolic kinetics, kinetic sorption, subgridscale averaging, pore clogging and protozoan grazing.
Date: December 31, 1998
Creator: Travis, B. J.
Partner: UNT Libraries Government Documents Department

Mercury Removal from Waste Oils

Description: Mercury was effectively removed from the oil via sorption using SAMMS.The method was demonstrated on a large scale using ORNL waste oil contaminated with mercury. This technology is ready for further demonstration and implementation when the SAMMS material is available in large quantities.
Date: June 20, 1999
Creator: Cummins, R.L.; Klasson, T. & Taylor, P.A.
Partner: UNT Libraries Government Documents Department

Mercury Removal from Waste Organics

Description: Mercury was effectively removed from the oil via sorption using SAMMS.The method was demonstrated on a large scale using ORNL waste oil contaminated with mercury. This technology is ready for further demonstration and implementation when the SAMMS material is available in large quantities.
Date: February 28, 1999
Creator: Cummins, R.L.; Klasson, T. & Taylor, P.A.
Partner: UNT Libraries Government Documents Department

Actinide biocolloid formation in brine by halophilic bacteria

Description: The authors examined the ability of a halophilic bacterium (WIPP 1A) isolated from the Waste Isolation Pilot Plant (WIPP) site to accumulate uranium in order to determine the potential for biocolloid facilitated actinide transport. The bacterial cell surface functional groups involved in the complexation of the actinide were determined by titration. Uranium, added as uranyl nitrate, was removed from solution at pH 5 by cells but at pH 7 and 9 very little uranium was removed due to its limited solubility. Although present as soluble species, uranyl citrate at pH 5, 7, and 9, and uranyl carbonate at pH 9 were not removed by the bacterium because they were not bioavailable due to their neutral or negative charge. Addition of uranyl EDTA to brine at pH 5, 7, and 9 resulted in the immediate precipitation of U. Transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) analysis revealed that uranium was not only associated with the cell surface but also accumulated intracellularly as uranium-enriched granules. Extended X-ray absorption fine structure (EXAFS) analysis of the bacterial cells indicated the bulk sample contained more than one uranium phase. Nevertheless these results show the potential for the formation of actinide bearing bacterial biocolloids that are strictly regulated by the speciation and bioavailability of the actinide.
Date: December 31, 1998
Creator: Gillow, J.B.; Francis, A.J.; Dodge, C.J.; Harris, R.; Beveridge, T.J.; Brady, P.V. et al.
Partner: UNT Libraries Government Documents Department

Irreversible Sorption of Contaminants During Ferrihydrite Transformation

Description: A better understanding of the fraction of contaminants irreversibly sorbed by minerals is necessary to effectively quantify bioavailability. Ferrihydrite, a poorly crystalline iron oxide, is a natural sink for sorbed contaminants. Contaminants may be sorbed/occluded as ferrihydrite precipitates in natural waters or as it ages and transforms to more crystalline iron oxides such as goethite or hematite. Laboratory studies indicate that Cd, Co, Cr, Cu, Ni, Np, Pb, Sr, U, and Zn are irreversibly sorbed to some extent during the aging and transformation of synthetic ferrihydrite. Barium, Ra and Sr are known to sorb on ferrihydrite in the pH range of 6 to 10 and sorb more strongly at pH values above its zero point of charge (pH> 8). We will review recent literature on metal retardation, including our laboratory and modeling investigation of Ba (as an analogue for Ra) and Sr adsorption/resorption, during ferrihydrite transformation to more crystalline iron oxides. Four ferrihydrite suspensions were aged at pH 12 and 50 °C with or without Ba in 0.01 M KN03 for 68 h or in 0.17 M KN03 for 3424 h. Two ferrihydrite suspensions were aged with and without Sr at pH 8 in 0.1 M KN03 at 70°C. Barium or Sr sorption, or resorption, was measured by periodically centrifuging suspension subsamples, filtering, and analyzing the filtrate for Ba or Sr. Solid subsamples were extracted with 0.2 M ammonium oxalate (pH 3 in the dark) and with 6 M HCl to determine the Fe and Ba or Sr attributed to ferrihydrite (or adsorbed on the goethite/hematite stiace) and the total Fe and Ba or Sr content, respectively. Barium or Sr occluded in goethite/hematite was determined by the difference between the total Ba or Sr and the oxalate extractable Ba or Sr. The percent transformation of ferrihydrite to goethite/hematite was estimated ...
Date: May 19, 1999
Creator: Anderson, H. L.; Arthur, S. E.; Brady, P. V.; Cygan, R. T.; Nagy, K. L. & Westrich, H. R.
Partner: UNT Libraries Government Documents Department

Chemometric Classification of Unknown Vapors by Conversion of Sensor Array Pattern Vectors to Vapor Descriptors: Extension from Mass-Transducing Sensors To Volume-Transducing Sensors

Description: A new chemometric method was recently described for classifying unknowns by transforming the vector containing the responses from a multivariate detector to a vector containing descriptors of the detected analyte (Grate et al. 1999). This approach was derived for sensor arrays where each sensor's signal is proportional to the amount of vapor sorbed by a polymer on the sensor surface. In this case, the response is proportional to the partition coefficient, K, and the concentration of the vapor in the gas phase, Cv, where K is the ratio of the concentration of vapor in the sorbent polymer phase, Cs, to Cv.
Date: June 28, 2001
Creator: Grate, Jay W
Partner: UNT Libraries Government Documents Department

Diffusion, Uptake and Release of Hydrogen in p-type Gallium Nitride: Theory and Experiment

Description: The diffusion, uptake, and release of H in p-type GaN are modeled employing state energies from density-function theory and compared with measurements of deuterium uptake and release using nuclear-reaction analysis. Good semiquantitative agreement is found when account is taken of a surface permeation barrier.
Date: June 27, 2000
Partner: UNT Libraries Government Documents Department

A simple extension of two-phase characteristic curves to include the dry region

Description: Two-phase characteristic curves are necessary for the simulation of water and vapor flow in porous media. Existing functions such as van Genuchten, Brooks and Corey, and Luckner et al. have significant limitations in the dry region as the liquid saturation goes to zero. This region, which is important in a number of applications including liquid and vapor flow and vapor-solid sorption, has been the subject of a number of previous investigations. Most previous studies extended standard capillary pressure curves into the adsorption region to zero water content and required a refitting of the revised curves to the data. In contrast, the present method provides for a simple extension of existing capillary pressure curves without the need to refit the experimental data. Therefore, previous curve fits can be used, and the transition between the existing fit and the relationship in the adsorption region is easily calculated. The data-model comparison shows good agreement. This extension is a simple and convenient way to extend existing curves to the dry region.
Date: January 25, 2000
Partner: UNT Libraries Government Documents Department

Data summary report for M.W. Kellogg Z-sorb sorbent tests. CRADA 92-008 Final report

Description: A series of tests were undertaken from August 6, 1992 through July 6, 1993 at METC`s High Pressure Bench-Scale Hot Gas Desulfurization Unit to support a Cooperative Research and Development Agreement (CRADA) between METC`s Sorbent Development Cluster and M.W. Kellogg. The M.W. Kellogg Company is currently developing a commercial offering of a hot gas clean-up system to be used in Integrated Gasification Combined Cycle (IGCC) systems. The intent of the CRADA agreement was to identify a suitable zinc-based desulfurization sorbent for the Sierra Pacific Power Company Clean Coal Technology Project, to identify optimum operating conditions for the sorbent, and to estimate potential sorbent loss per year. This report presents results pertaining to Phillips Petroleum`s Z-Sorb III sorbent.
Date: May 1994
Creator: Everett, C. E. & Monaco, S .J.
Partner: UNT Libraries Government Documents Department

The efficacy of oxidative coupling for promoting in-situ immobilization of hydroxylated aromatics in contaminated soil and sediment systems. 1998 annual progress report

Description: 'Hydroxylated aromatic compounds (HAC''s) and their precursors are common contaminants of surface and subsurface systems at DOE facilities. The environmental fate and transport of such compounds, particularly in subsurface systems, is generally dominated by their sorption and desorption by soils and sediments. Certain secondary chemical reactions, most specifically abiotic and/or enzymatic oxidative coupling, may be significant in controlling the sorption and subsequent desorption of such hydroxylated aromatics by soils and sediments. The principal objectives of this study are to investigate: (1) the role of abiotic/enzymatic coupling reactions on the immobilization of HAC''s; (2) the effects of environmental factors on such immobilization; and (3) preliminary engineering approaches utilizing enhanced abiotic/enzymatic coupling reactions to immobilize hydroxylated aromatics in-situ. Information gathered from the study will be useful in quantifying the behavior of this class of organic compounds in various subsurface contamination scenarios relevant to DOE facilities, and in specifying strategies for the selection and design of remediation technologies. Over the first two years of this three-year project, the authors have developed a significantly improved understanding of the mechanisms of hydroxylated aromatic compound sorption and immobilization by natural soils and sediments. Immobilization in this context is attributed to oxidative coupling of the hydroxylated aromatics subsequent to their sorption to a soil or sediment, and is quantified in terms of the amount of a sorbed target compound retained by a sorbent after a series of sequential water and solvent extractions. The presence of oxygen, metal oxides, and organic matter, all of which can potentially catalyze/facilitate the abiotic oxidative coupling of HAC''s, were investigated during these first two years. Three different HAC''s: phenol, trichlorophenol and o-cresol were included in the experimental program. Inorganic soil matrices were represented by a glacial wash sand (Wurtsmith sand) having very low organic content. Because the chemical nature of soil organic ...
Date: June 1, 1998
Creator: Weber, W.J. & Bhandari, A.
Partner: UNT Libraries Government Documents Department

Permanganate treatment of DNAPLs in reactive barriers and source zone flooding schemes. 1997 annual progress report

Description: 'The goals of this study are (1) to elucidate the basic mechanisms by which potassium permanganate oxidizes common chlorinated solvents, various constituents in aqueous solution, and porous-medium solids, and (2) to assess the potential for chemical oxidation by potassium permanganate to serve as a remedial scheme involving either source zone flooding or reactive barriers. The research plan involves a combined experimental/modeling study that builds on the extensive previous work in the area of reactive barrier systems, and modeling of reactive contaminant transport. The experimental studies are being undertaken at The Ohio State University by Dr. Schwartz and his co-workers. The modeling work is being conducted in Albuquerque, NM by Dr. Zhang of Intera, Inc. The workplan for this study is designed around the following four objectives (1) to describe through batch experiments the kinetics and mechanisms by which potassium permanganate oxidizes dissolved tetrachloroethene (PCE), trichloroethene (TCE), and dichloroethene (DCE), (2) to examine using column studies the nature and kinetics of reactions between potassium permanganate, residual DNAPLs (PCE, TCE, and DCE) and porous medium solids, (3) to represent the process understanding in flow and transport models that demonstrate the potential applicability of the approach, and (4) to apply the resulting computer code in the development of appropriate field tests for assessing the approach.'
Date: January 1, 1997
Creator: Schwartz, F.W.
Partner: UNT Libraries Government Documents Department

Experimental determination of contaminant metal mobility as a function of temperature time and solution. 1998 annual progress report

Description: 'The objective of this work is to determine the fundamental data needed to predict the behavior of {sup 90}Sr at temperature and time scales appropriate to thermal remediation. The authors approach combines macroscopic sorption/precipitation and desorption/dissolution kinetic experiments which track changes in solution composition with direct molecular characterization of Sr in the solid phase using x-ray absorption spectroscopy. These experiments will be used to identify mechanistic geochemical reactions and their thermochemical properties that will be incorporated into geochemical computer codes. As of May 1998, the authors have completed most of the static sorption experiments as a function of temperature (25, 60, and 80 C), solution pH (4 to 10), initial Sr concentrations (10{sup -7} to 10{sup -3} M), and partial pressure of CO 2 (100% N 2 or atmospheric CO 2 ). They chose to study goethite, kaolinite, gibbsite, and amorphous silica because iron and aluminum (oxy)hydroxides, aluminosilicate clays, and quartz are key components in soils, sediments, and aquifers. The authors have completed x-ray absorption analysis of Sr sorption to kaolinite and goethite at 25{sup -}C, initial Sr of 10{sup -}3 M, and pH 9.'
Date: June 1, 1998
Creator: Carroll, S.; Bruton, C.; O'Day, P. & Sahai, N.
Partner: UNT Libraries Government Documents Department

Permanganate treatment of DnAPLs in reactive barriers and source zone flooding schemes. 1998 annual progress report

Description: 'The goals of this study are: (1) to elucidate the basic mechanisms by which potassium permanganate oxidizes common chlorinated solvents, various constituents in aqueous solution, and porous-medium solids, and (2) to assess the potential for chemical oxidation by potassium permanganate to serve as a remedial scheme involving either source zone flooding or reactive barriers. The combined theoretical and experimental study is designed to contribute fundamental knowledge about reaction pathways, reaction rates, specific intermediates formed, and controls on reaction processes. The specific objectives of this study are: (1) to describe through batch experiments the kinetics and mechanisms by which potassium permanganate oxidizes dissolved tetrachloroethene (PCE), trichloroethene (TCE), and dichloroethene (DCE), (2) to examine using column studies the nature and kinetics of reactions between potassium permanganate, residual DNAPLs (PCE, TCE, and DCE) and porous medium solids, (3) to represent the process understanding in flow and transport models that demonstrate the potential applicability of the approach, and (4) to apply the resulting computer code in the development of appropriate field tests for assessing the approach. Approaching the end of Year 2 of this 3-Year project, the authors can report significant progress in meeting the objectives of the study. Through a series of batch experiments, it has been shown that permanganate oxidation is effective in degrading various chlorinated ethylenes in aqueous solution. The disappearance of chlorinated ethylenes can be simply characterized by a pseudo-first-order model. Degradation half-lives for TCE, cis-1,2-DCE, trans-1,2-DCE and 1,1-DCE reacting with 1mM MnO{sub 4}{sup -} range from about 24 s to 18 min. Degradation of PCE is much slower with a half-life of about 257 min. Overall, the degradation rate is inversely proportional to the number of chlorines present as substituents on ethylenes. These rates of degradation are impressive given the fact that the experiments were run with MnO{sub 4}{sup ...
Date: June 1, 1998
Creator: Schwartz, F.W. & Zhang, Hubao
Partner: UNT Libraries Government Documents Department

Outer Sphere Adsorption of Pb(II)EDTA on Goethite

Description: FTIR and EXAFS spectroscopic measurements were performed on Pb(II)EDTA adsorbed on goethite as functions of pH (4-6), Pb(II)EDTA concentration (0.11 {micro}M - 72 {micro}M), and ionic strength (16 {micro}M - 0.5M). FTIR measurements show no evidence for carboxylate-Fe(III) bonding or protonation of EDTA at Pb:EDTA = 1:1. Both FTIR and EXAFS measurements suggest that EDTA acts as a hexadentate ligand, with all four of its carboxylate and both amine groups bonded to Pb(II). No evidence was observed for inner-sphere Pb(II)-goethite bonding at Pb:EDTA = 1:1. Hence, the adsorbed complexes should have composition Pb(II)EDTA{sup 2{minus}}. Since substantial uptake of PbEDTA(II){sup 2{minus}} occurred in the samples, we infer that Pb(II)EDTA{sup 2{minus}} adsorbed as outer-sphere complexes and/or as complexes that lose part of their solvation shells and hydrogen bond directly to goethite surface sites. We propose the term ''hydration-sphere'' for the latter type of complexes because they should occupy space in the primary hydration spheres of goethite surface functional groups, and to distinguish this mode of sorption from common structural definitions of inner- and outer-sphere complexes. The similarity of Pb(II) uptake isotherms to those of other divalent metal ions complexed by EDTA suggests that they too adsorb by these mechanisms. The lack of evidence for inner-sphere EDTA-Fe(III) bonding suggests that previously proposed metal-ligand - promoted dissolution mechanisms should be modified, specifically to account for the presence of outer-sphere precursor species.
Date: July 16, 1999
Creator: Bargar, John R
Partner: UNT Libraries Government Documents Department

Molecular-level process governing the interaction of contaminants with iron and manganese oxides. 1998 annual progress report

Description: 'The authors are carrying out a program of research that focuses on the fundamental mechanisms of redox chemistry of contaminants on mineral surfaces. As much of this chemistry in sediments involves the Fe(III)/Fe(II) and Mn(IV)/Mn(II) couples, they are focusing on mineral phases containing these species. The authors are using a variety of experimental probes, along with molecular modeling theory, to determine clean mineral surface structure and morphology, details of the chemisorption and decomposition of water, and the interface structure and redox chemistry of important contaminants such as CrO{sub 4}{sup -2} on these surfaces. Insight gained in this project will aid in the formulation of more accurate and realistic contaminant-surface complexation and contaminant transport models, and may suggest improved remediation strategies for certain kinds of contaminated soil and groundwater.'
Date: June 1, 1998
Creator: Chambers, S. A. & Brown, G. E.
Partner: UNT Libraries Government Documents Department