Skip to main content
Advanced Search

Folders: ROOT > ScienceBase Catalog > USGS National Research Program > USGS National Research Program Projects > Partitioning of Solutes Between Solid and Aqueous Phases ( Show all descendants )

85 results (177ms)   

Location

Folder
ROOT
_ScienceBase Catalog
__USGS National Research Program
___USGS National Research Program Projects
____Partitioning of Solutes Between Solid and Aqueous Phases
View Results as: JSON ATOM CSV
In many subsurface situations where human health and environmental quality are at risk (e.g., contaminant hydrogeology petroleum extraction, carbon sequestration, etc.),scientists and engineers are being asked by federal agency decision-makers to predict the fate of chemical species under conditions where both reactions and transport are processes of first-order importance.In 2002, a working group (WG) was formed by representatives of the U.S. Geological Survey, Environmental Protection Agency, Department of Energy Nuclear Regulatory Commission, Department of Agriculture, and Army Engineer Research and Development Center to assess the role of reactive transport modeling (RTM) in addressing these situations. Specifically...
X-ray diffraction [crystal-truncation-rod (CTR)] studies of the surface structure of moisture-equilibrated hematite reveal sites for complexation not present on the bulk oxygen-terminated surface, and impose constraints on the types of inner-sphere sorption topologies. We have used this improved model of the hematite surface to analyze grazing-incidence EXAFS results for arsenate sorption on the c (0001) and r (10–12) surfaces measured in two electric vector polarizations. This work shows that the reconfiguration of the surface under moist conditions is responsible for an increased adsorption density of arsenate complexes on the (0001) surface relative to predicted ideal termination, and an abundance of “edge-sharing”...
The reactive transport of U(VI) in a well-characterized shallow alluvial aquifer at a former U(VI) mill located near Naturita, CO, was predicted for comparative purposes using a surface complexation model (SCM) and a constant K d approach to simulate U(VI) adsorption. The ground water at the site had U(VI) concentrations that ranged from 0.01 to 20 µM, alkalinities that ranged from 2.5 to 18 meq/L, and a nearly constant pH of 7.1. The SCM used to simulate U(VI) adsorption was previously determined independently using laboratory batch adsorption experiments. Simulations obtained using the SCM approach were compared with simulations that used a constant K d approach to simulate adsorption using previously determined...
Recent studies of uranium(VI) geochemistry have focused on the potentially important role of the aqueous species, CaUO2(CO3)32− and Ca2UO2(CO3)30(aq), on inhibition of microbial reduction and uranium(VI) aqueous speciation in contaminated groundwater. However, to our knowledge, there have been no direct studies of the effects of these species on U(VI) adsorption by mineral phases. The sorption of U(VI) on quartz and ferrihydrite was investigated in NaNO3 solutions equilibrated with either ambient air (430 ppm CO2) or 2% CO2 in the presence of 0, 1.8, or 8.9 mM Ca2+. Under conditions where the Ca2UO2(CO3)30(aq) species predominates U(VI) aqueous speciation, the presence of Ca in solution lowered U(VI) adsorption...
Categories: Publication; Types: Citation
We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic (As) in a shallow, sand and gravel aquifer with distinct geochemical zones resulting from land disposal of dilute sewage effluent. The principal geochemical zones were: (1) the uncontaminated zone above the sewage plume [350 µM dissolved oxygen (DO), pH 5.9]; (2) the suboxic zone (5 µM DO, pH 6.2, elevated concentrations of sewage-derived phosphate and nitrate); and (3) the anoxic zone [dissolved iron(II) 100–300 µM, pH 6.5–6.9, elevated concentrations of sewage-derived phosphate]. Sediments are comprised of greater than 90% quartz but the surfaces of quartz and other mineral grains are...
Assessing the quantity of U(VI) that participates in sorption/desorption processes in a contaminated aquifer is an important task when investigating U migration behavior. U-contaminated aquifer sediments were obtained from 16 different locations at a former U mill tailings site at Naturita, CO (U.S.A.) and were extracted with an artificial groundwater, a high pH sodium bicarbonate solution, hydroxylamine hydrochloride solution, and concentrated nitric acid. With an isotopic exchange method, both a KD value for the specific experimental conditions as well as the total exchangeable mass of U(VI) was determined. Except for one sample, KD values determined by isotopic exchange with U-contaminated sediments that were...
Categories: Publication; Types: Citation
The discharge of a plume of sewagecontaminated ground water emanating from the Massachusetts Military Reservation to Ashumet Pond on Cape Cod, Massachusetts, has caused concern about excessive loading of nutrients, particularly phosphorus, to the pond. The U.S. Air Force is considering remedial actions to mitigate potentially adverse effects on the ecological characteristics of the pond from continued phosphorus loading. Concentrations as great as 3 milligrams per liter of dissolved phosphorus (as P) are in ground water near the pond‘s shoreline; concentrations greater than 5 milligrams per liter of phosphorus are in ground water farther upgradient. Temporary drive-point wells were used to collect water samples...
Categories: Publication; Types: Citation
The adsorption of uranyl on standard Georgia kaolinites (KGa-1 and KGa-1B) was studied as a function of pH (3–10), total U (1 and 10 μmol/l), and mass loading of clay (4 and 40 g/l). The uptake of uranyl in air-equilibrated systems increased with pH and reached a maximum in the near-neutral pH range. At higher pH values, the sorption decreased due to the presence of aqueous uranyl carbonate complexes. One kaolinite sample was examined after the uranyl uptake experiments by transmission electron microscopy (TEM), using energy dispersive X-ray spectroscopy (EDS) to determine the U content. It was found that uranium was preferentially adsorbed by Ti-rich impurity phases (predominantly anatase), which are present in...
The effects of Hurricanes Katrina and Rita and the subsequent unwatering of New Orleans, Louisiana, on the sediment chemistry of Lake Pontchartrain were evaluated by chemical analysis of samples of street mud and suspended and bottom sediments. The highest concentrations of urban-related elements and compounds (e.g., Pb, Zn, polycyclic aromatic hydrocarbons, and chlordane) in bottom sediments exceeded median concentrations in U.S. urban lakes and sediment-quality guidelines. The extent of the elevated concentrations was limited, however, to within a few hundred meters of the mouth of the 17th Street Canal, similar to results of historical assessments. Chemical and radionuclide analysis of pre- and post-Hurricane...
Categories: Publication; Types: Citation
Experimental data for uranium adsorption on a complex weathered rock were simulated by twelve modelling teams from eight countries using surface complexation (SC) models. This intercomparison was part of an international project to evaluate the present capabilities and limitations of SC models in representing sorption by geologic materials. The models were assessed in terms of their predictive ability, data requirements, number of optimised parameters, ability to simulate diverse chemical conditions and transferability to other substrates. A particular aim was to compare the generalised composite (GC) and component additivity (CA) approaches for modelling sorption by complex substrates. Both types of SC models showed...
Categories: Publication; Types: Citation
We investigated arsenate (As(V)) reactivity and surface speciation on amorphous aluminosilicate mineral (synthetic allophane) surfaces using batch adsorption experiments, powder X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). The adsorption isotherm experiments indicated that As(V) uptake increased with increasing [As(V)]o from 50 to 1000 ?M (i.e., Langmuir type adsorption isotherm) and that the total As adsorption slightly decreased with increasing NaCl concentrations from 0.01 to 0.1 M. Arsenate adsorption was initially (0?10 h) rapid followed by a slow continuum uptake, and the adsorption processes reached the steady state after 720 h. X-ray absorption spectroscopic analyses suggest that As(V)...
Categories: Publication; Types: Citation
Effects of dissolved carbonate on arsenate [As(V)] reactivity and surface speciation at the hematite?water interface were studied as a function of pH and two different partial pressures of carbon dioxide gas [PCO2 = 10-3.5 atm and ?0; CO2-free argon (Ar)] using adsorption kinetics, pseudo-equilibrium adsorption/titration experiments, extended X-ray absorption fine structure spectroscopic (EXAFS) analyses, and surface complexation modeling. Different adsorbed carbonate concentrations, due to the two different atmospheric systems, resulted in an enhanced and/or suppressed extent of As(V) adsorption. As(V) adsorption kinetics [4 g L-1, [As(V)]0 = 1.5 mM and I = 0.01 M NaCl] showed carbonate-enhanced As(V) uptake in...
Categories: Publication; Types: Citation
The microbial catalysis of Mn(II) oxidation is believed to be a dominant source of abundant sorption- and redox-active Mn oxides in marine, freshwater, and subsurface aquatic environments. In spite of their importance, environmental oxides of known biogenic origin have generally not been characterized in detail from a structural perspective. Hyporheic zone Mn oxide grain coatings at Pinal Creek, Arizona, a metals-contaminated stream, have been identified as being dominantly microbial in origin and are well studied from bulk chemistry and contaminant hydrology perspectives. This site thus presents an excellent opportunity to study the structures of terrestrial microbial Mn oxides in detail. XRD and EXAFS measurements...
Categories: Publication; Types: Citation
To study transport and reactions of arsenic under field conditions, a small-scale tracer test was performed in an anoxic, iron-reducing zone of a sandy aquifer at the USGS research site on Cape Cod, Massachusetts, USA. For four weeks, a stream of groundwater with added As(V) (6.7 μM) and bromide (1.6 mM), was injected in order to observe the reduction of As(V) to As(III). Breakthrough of bromide (Br−), As(V), and As(III) as well as additional parameters characterizing the geochemical conditions was observed at various locations downstream of the injection well over a period of 104 days. After a short lag period, nitrate and dissolved oxygen from the injectate oxidized ferrous iron and As(V) became bound to the freshly...
The reactive transport of U(VI) in a shallow alluvial aquifer beneath a former U(VI) mill located near Naturita, CO, was simulated using a surface complexation model (SCM) to describe U(VI) adsorption. The groundwater had variable U(VI) concentrations (0.01–20 μM), variable alkalinity (2.5–18 meq/L), and a nearly constant pH equal to 7.1. U(VI) KD values decreased with increasing U(VI) and alkalinity, and these parameters were more important than sediment variability in controlling KD values. Reactive transport simulations were fit to the observed U(VI) and alkalinity by varying the concentration of U(VI) and alkalinity in recharge at the source area. Simulated KD values varied temporally and spatially because of...
At the Naturita site in Colorado, USA, groundwaters were sampled and analyzed for chemical composition and by culture and culture-independent microbiological techniques. In addition, sediments were extracted with a dilute sodium carbonate solution to determine quantities of labile uranium within the sediments. Samples from the upgradient portion of the contaminated aquifer, where very little dissolved Fe(II) is found in the groundwater, have uranium content that is controlled by U(VI) adsorption and few metal-reducing bacteria are observed. In the extreme downgradient portion of the aquifer, where dissolved Fe(II) is observed, uranium content of the sediments includes significant quantities of reduced U(IV) and...