<p>The crystal structures of three cancrinites, four sodalites, six helvites and tugtupite have been refined using x-ray diffraction data. The nature of the crystal structure and crystal chemistry of the cancrinites and sodalites have been elucidated, with emphasis on 1) the significance of the superstructures, 2) the space group problem, 3) the order-disorder, 4) the structural variation, and 5) the stoichiometry. Also, a geometrical structural model for sodalite ha been developed and it has the following uses: a) Allows the accurate prediction of the structures of all members of the sodalite group of minerals. b) The prediction of the chemical limits of structural stability of all materials based on the sodalite structural type. c) Permits the published thermal expansion data for sodalites to be rationalized in terms of rotation of the Al/Si-0₄ tetrahedra.</p> / Doctor of Philosophy (PhD)

<p>After a recapitulation of complexation theory, a theory is developed for the determination of copper complexation for mono- and bidentate complexes and for 2:1 complexes (CuL₂) by ion exchange. This theory can be applied in principle to other ion exchange methods that make use of weak ion exchange media with an adsorption behavior of metal ions similar to Langmuir adsorption. From this theory it has been deduced that titration with Cu²⁺ of a single ligand, in presence of a weak ion exchange medium, can be graphically represented by a straight line; slope and intercept with the Y-axis provide information on the conditional stability constant and the ligand concentration. In certain conditions similar data may be obtained for a second ligand, from a single titration of the sample with Cu²⁺ at fixed pH.</p> <p>An aged dispersion of MnO₂ is used as an ion exchange medium to determine complexing capacities of natural waters and conditional stability constants for complexes with copper ions. The method is sufficiently sensitive to apply to original water samples: no pre-concentration is necessary. Limits of detection are a minimum of 0.15 μM ligands and log conditional stability constants (log K') between 6 and 10 at pH 8, analyses may be performed at any pH between 6 and 9.</p> <p>For fulvic acid (FA) and for ligands in dystrophic rivers log K' = ~7.8 at pH 7.6, the ligand concentration is 5-30 μM; for ligands in lakes log K' ranges from 7.6 to 8.5 at pH 7.6, the ligand concentration is 0.2-3 μM. Generally only one ligand is dominantly present. From pH 5 to 9 the state of copper in natural waters is regulated by organic complexing ligands.</p> <p>Literature survey shows that conditional stability constants for complexes of humic acids (HAs) and FAs with Cu²⁺ have a constant relationship with the pH: log K' = pH -0.5, when 5 < pH < 8.5; for the same pH limits, the affinity of HAs and FAs for protons is about 3x larger than for Cu²⁺ ions. K' values for natural ligands analysed with the Mn°2 method also vary with the pH on a 1:1 basis of log K' vs. pH. Apparently a proton is exchanged for each Cu²⁺ ion bound.</p> <p>Three algal species, Anabaena cylindrica, Navicula pelliculosa and Scenedesmus quadricauda excreted 6.73, 2.86, and 0.66 μM of complexing ligands, respectively, with values for log K' of 7.7, 8.1, and 8.6, respectively, for complexes with copper. A free copper ion concentration of 10ˉ¹⁰˙³ M is calculated for each exudate, while in lakes a concentration of 10ˉ⁹˙⁸ to 10ˉ¹⁰˙² M is found. Algal exudates are similar in complexing ability to some amino acids and to ligands in lakes, and ameliorate toxicity of copper ions to the primary production of Chlorella vulgaris. From model calculation it is apparent that in presence of dissolved organic ligands toxicity or availability of Cu²⁺ to phytoplankton does not depend on pH, for 5.5 < pH < 8 and low Pco₂.</p> / Doctor of Philosophy (PhD)

<p>Dimethyl sulfide (OMS) is the major volatile sulfide (VS) species of biogenic origin released to the atmosphere. Large amounts of OMS can originate from the decomposition of the metabolic precursor Dimethylsulfoniopropionate (DMSP) in marine algae. Quantitatively, the emissions of OMS and other VS to the atmosphere are in the same order of magnitude as atmospheric sulfur from man-made pollution. Therefore the study of OMS and other VS has a significant relevance to atmospheric chemistry.</p> <p>Early studies on OMS focused on the marine environment and coastal waters. The presence of other biogenic species such as H₂S, COS, CS₂, CH₃SH (MeSH), CH₃SSCH₃ (DMDS) was also detected in various types of environments including salt ponds, meromictic lakes, soils, freshwaters.</p> <p>The present work is a laboratory-oriented study on the processes of formation of VS from freshwater algae. The approach undertaken is threefold: 1) Establish the presence and/or production of OMS and possibly other VS from algae cultures and surrounding lake waters. 2) Identify some key parameters influencing the formation of VS from freshwater algae. 3) Estimate the atmospheric contribution of VS from some freshwater algae and lakes.</p> <p>This study showed that all species of algae and all natural waters contain OMS in amounts comparable to marine waters. However, in contrast to marine waters, OMS generally constitutes only 5 to 25% of all the sulfides, whereas MeSH usually predominates (40-80 %). H₂S+COS, CS₂ and DMDS are commonly present, whereas other species are rarely detected.</p> <p>Changes in sulfate concentration had 115 significant effect on VS production by algae, but there was a threshold level of about 2 mg/L SO₄ for VS production. Cysteine also caused no significant change in VS production, but a small influence was observed with the addition of methyl donors. Methionine holds a key part in formation of methylated sulfides: additions provoked an increase of MeSH and DMDS production by up to 2 or 3 orders of magnitude.</p> <p>Calculations suggest that VS from freshwater algae contribute about 115 tons S/year in Lake Ontario. This estimate is quite variable, but it is small compared to other sulfur inputs, including pollution.</p> / Doctor of Philosophy (PhD)

<p>The Th²³⁰/U²³⁴ and U²³⁴/U²³⁸ ratios of speleothems (calcareous deposits) from caves developed in limestones of the Greenbrier Series, S.E. West Virginia, was measured by alpha-particle spectrometry to assess the deficient Th²³⁰ (ionium) and excess U²³⁴ dating methods respectively. Pure, non-porous, very coarsely crystalline deposits showing no signs of submersion or re-solution were found to be suitable for Th²³⁰/U²³⁴ dating. This method was used to date deposits between about 2000 and 300,000 years old. The decay of excess U²³⁴, which in principle can be used to date deposits 50,000 to 1,500,000 years old, could not be used as a routine method because the initial excess of U²³⁴ could not be reliably determined. Concordant Pa²³¹/Th²³⁰ and Th²³⁰/U²³⁴ ages were measured for two samples from West Virginia.</p> <p>Norman-Bone Cave and Grapevine Cave, both in Greenbrier Co., were studied in detail. Norman-Bone Cave contains speleothems at least 300,000 years old. Based on the decay of U²³⁴, one stalagmite appeared to have been deposited between about 760,000 years and 1,250,000 years B.P. Speleothem ages from caves in the Crowsnest Pass area of Alberta, the Nahanni region of the North West Territories and the Ciudad Valles area of Mexico were also obtained. With the exception of the single Mexican sample, deposition appears to stop during prolonged periods of cold climate; therefore a continuous record of CaCO₃ deposition is not preserved in the northern caves. Based on the gaps in the recota, the coldest periods of the Wisconsin, Illinoian and Kansan (?) glacial ages occur between 20-35,000, 135-160,000 and 240-270,000 years B.P. respectively. The intervening periods are times of cool to warm, moist climate which favour speleothem deposition.</p> <p>The ratio O¹⁸/O¹⁶ (δºct) and c¹³/C¹² (δºct) in young and fossil speleothems deposited in isotopic equilibrium with parent waters was measured in an attempt to construct detailed climate curves for the Late Pleistocene. Five young speleothems all appeared to be deposited in isotopic equilibrium: an isotopic temperature of 8.6±1.6ºc was calculated, 2.3ºC lower than the present mean annual surface air temperature. The discrepancy could be real, for cave temperatures are often slightly lower than mean annual surface air temperatures.</p> <p>Variations inδºct and δºct in two dated stalagmites from Norman-Bone Cave (NB4 and NB10) and a flowstone deposit from Grapevine Cave (GV2) are commonly uncorrelated within individual depositional layers, satisfying Hendy's criteria for CaCO₃ deposition in oxygen isotopic equilibrium with water. Parts of NB4 and GV2, which were deposited contemporaneously about 100,000 years ago record the same temperature maximum.</p> <p>Cyclic secular variations δºct cannot be interpreted in terms of climat change without knowledge of variations in 60 of waters depositing the CaCO₃. An attempt was made to measure these variations directly by extracting water from fluid inclusions in the fossil deposits. The D/H (δᵢD) ratio of the water was measured and the Craig-Dansgaard relationship (δᵢD =86ᵢº + 10) applied to calculate δºᵢ (≡δºw). Absolute temperatures calculated from δºw and δºct are, in general too low but with further refinements the method may become a valuable tool for paleoclimatologists.</p> <p>In general, δºct is found to increase in calcite deposited at lower temperatures. This is attributed to the deposition of CaCO₃ from waters of relatively constant isotopic composition, so that changes in δºct are determined by the effect of temperature on the CaCO₃-H₂O fractionation factor. (0.24‰ increase per 1ºC temperature drop).</p> <p>The relative constancy of δºw values of cave drip-waters is attributed to seasonal CaCO₃ deposition from waters whose isotopic composition is biassed toward mean summer values. As mean annual temperatures decrease, CaCO₃ deposition is from waters which are progressively biassed in isotopic composition toward the mean July value.</p> <p>Temperature maxima are recorded in GV2 at 80.000±3000 years B.P. and 100.000±4000 years B.P.; a lower maximum is recorded at 60.000±3000 years B.P. Temperature maxima in NB10 are recorded at 163,000±6800, 170,000±7000 and 180,000±9700 years B.P. An intensely cold period is recorded between 180,000 and 170,000 years B.P. which was inferred to be colder than any event recorded in GV2 between 100,000 and 60,000 years B.P.</p> <p>δºct also increases as regional temperatures decrease. probably as a result of the decreased rate of plant respiration, microbial activity and CO₂ production in the soil during cold periods. The δºct variations are not well enough defined to be used as a reliable indicator of climate change.</p> <p>Good correlation is observed with the time-temperature curve for Wisconsin glaciation and the Sangamom interglacial, as obtained from deep-sea cores and raised coral reefs. Correlation with the penultimate (Illinoian) glaciation and preceding (Yarmouth) interglacial is unclear.</p> / Doctor of Philosophy (PhD)

<p>This study evaluates: (1) the use of a radiotracer technique to obtain kinetic data on trace metal interactions with sediments in a freshwater environment, and (2) the importance of kinetic considerations in trace metal partitioning between sediment and water in a lake. The technique consists of measuring the distribution of a small radiotracer spike between the sediment and the aqueous phase over time. The system is assumed to be at equilibrium prior to spiking. The radiotracer uptake by sediments is first determined, the aqueous phase is then replaced by a non-tracer solution, and finally the tracer release is measured. Preliminary studies with cadmium and zinc showed: (1) stable solution conditions (no tracer added) with negligible change in trace metal concentrations and master parameters (pH, DOC) over several weeks, (2) precision in replicate analysis and experiments, and (3) confirmation of the technique as demonstrated with a synthetic TiO₂ suspension. A novel experimental design was devised, consisting of a kinetic model fitting using the "adsorption" kinetic data, followed by confirmation comparing the model data to "desorption" kinetic data. The technique was applied to surficial samples from three lacustrine systems using ⁶⁵Zn and ¹⁰⁹Cd. The kinetics of metal exchange are very similar for all samples for both "adsorption" and "desorption". The general kinetic behaviour was a fast reaction (hours) followed by a slower interaction (weeks). Three kinetic models were investigated to explain the "adsorption-desorption" data. A two-box model (TBM), describes the system as a reversible solid-liquid first-order reaction. It does not, however, explain the slower exchange well. Two other models include two distinctive kinetic reactions. They differ mostly by the nature of the "desorption" reaction prediction. A "two-box model with a leak" (TBL) considers a fast reversible first-order reaction followed by a slower first-order reaction (leak). A "restricted three-box model" (RTB) considers two independent reactions, both first-order and reversible, but of different rates. The TBL and RTB models can be fitted to the "adsorption" data very well. The "desorption" data is, however, better predicted by the TBL model revealing the slower short-term (hours-days) interactions of trace metals with lake sediments. Trace metal partitioning determined by short-term (hours-days) interactions gives higher solution concentration than longer-term (weeks-months) "equilibrium" partitioning. Thus short-term prediction of metal partitioning based on long-term "equilibrium" distribution would overestimate the role of natural sediments as metal sinks. This kinetic approach gives good estimates of the uptake and release of trace metals between sediment and water in lacustrine systems.</p> / Doctor of Philosophy (PhD)

Activities related to nuclear weapons production have left a legacy of uranium contamination in the United States. Understanding the chemical interactions that uranium undergoes in the environment is important for prediction of uranium mobility and development of remediation strategies. A detailed spectroscopic examination of the pH-dependent behavior of the UO₂²⁺-citrate system in aqueous solution was completed using Raman, ATR-FTIR, and NMR spectroscopies, combined with ESI-MS. Three structurally-distinct UO₂²⁺-citrate complexes, {(UO₂)₂Cit2}²⁻, {(UO₂)₃Cit₃}³⁻, and (UO₂)₃Cit₂ exist in dynamic equilibrium over a pH range from 2 to 9. ¹⁷O and ¹³C NMR data confirm the previously published structure of {(UO₂)₂Cit₂}²⁻ and indicate that {(UO₂)₃Cit₃}³⁻ is a symmetric, fluxional molecule. The (UO₂)₃Cit₂ complex was found to have a rigid structure and two structural isomers. Chemical interactions of U(VI), citric acid and Al₂O₃ were investigated using ATR-FTIR spectroscopy to examine how complexation of U(VI) by citrate affects adsorption of U(VI) to Al₂O₃. Participation in UO₂²⁺-citrate complexes does not significantly affect the ability of citrate to chemisorb to Al₂O₃. The UO₂²⁺-citrate complexes dissociate upon adsorption, with hydrolysis of UO₂²⁺. Adsorption isotherms developed from ATR-FTIR data indicate enhanced citrate adsorption to Al₂O₃ in the presence of UO₂²⁺ , suggesting that UO₂²⁺ acts as a central link between two citrate ligands, one of which is complexed to Al₂O₃. UO₂²⁺-citrate complexes can physisorb to citrate-saturated Al₂O₃. This study demonstrates how an in-depth infrared spectroscopic analysis of UO₂²⁺-ligand complexes both in solution and adsorbed to oxide surfaces can be used to understand the adsorption mechanisms of these complexes. ESI-MS was investigated for the characterization of U(VI) species in groundwater. Both ion trap and FTICR instruments were used. UO₂²⁺ forms complexes with ligands such as acetate, trifluoroacetate, and nitrate, which readily react with CH₃CN, CH₃OH, and H₂O to form solvated gas-phase species of the form [(UO₂L)Sn]⁺, where L represents the ligand, S represents solvent, and 1 ≤ n ≤ 4. n is directly related to the number of available coordination sites on UO₂²⁺, providing insight into the coordination environment of UO₂²⁺. Solvent exchange and addition reactions readily occur. UO₂²⁺ also forms coordinately saturated negatively-charged complexes with nitrate. UO₂²⁺-carbonate complexes were also investigated.

Thesis (M.S. - Hydrology and Water Resources)--University of Arizona, 1986. / Includes bibliographical references (leaves 68-72).

Researchers have expressed concern about pollution of groundwater at Coastal Park, a large, general waste landfill situated on the False Bay coastline above the Cape Flats Aquifer. The landfill was constructed without a liner, but with an average 2m separation of calcareous sand providing a "buffer" zone between the waste pile and the water table. Water balance studies and application of a model, FLOW, have predicted that leachate will be generated seasonally. This study was initiated as a result of uncertainties about hydrological and geochemical aspects, such as the hydraulic conductivity of the soil in the buffer zone and the degree of leachate attenuation occurring in this zone. The Coastal Park soil was classified as an aeolian, calcareous, medium quartzitic sand with negligible organic carbon content. Extreme clay-depletion would render the soil almost incapable of leachate attenuation, although calcite and aragonite, found by X-ray diffractometry, would impart a significant pH buffering capacity to the soil. The solid phase of a locally-derived landfill leachate (sampled from Vissershok landfill, about 35 km NW of Cape Town) was found to contain amorphous sulfides of iron and heavy metals, and green rusts which are mixtures of Fe²⁺ - Fe³⁺ hydroxides, in addition to organic matter. The solid phase was isolated by centrifugation, freeze-dried, and analyzed by XRF and XRD. Distribution coefficients of heavy metals in the leachate (at pH 7.7) demonstrated the high affinity of heavy metals, such as Cu, Zn, Cr, Ni and Pb, for the solid phase. The leachate solid phase consists of amorphous solids, with high Ca and Cl concentrations in the liquid phase leading to halite and calcite formation upon evaporation of the liquid phase. According to locally specified requirements by Department of Water Affairs and Forestry, a landfill liner material must have a hydraulic conductivity (K) not higher than 1 x 10⁻⁷cm.s⁻¹. Air dried samples of Coastal Park soil were treated with various amendments to test their efficacy as landfill liners. An 8 % kaolinite plus 4 % gypsum treatment was the most effective, maintaining a minimum K of 10⁻⁴⁵ cm.s⁻¹, which, however, is still higher than the local requirement. Amendment with 8 % Na-bentonite initially achieved a minimum K of 10⁻⁷·⁸ cm.s⁻¹, but the high electrical conductivity (EC) of the leachate (26.8mS.cm⁻¹) caused shrinking and severe side-wall seepage, which rapidly enhanced hydraulic conductivity, reaching a maximum K of about 10⁻⁴·⁷ cm.s⁻¹. Both treatments of the sand do show promise as possible liners, although the use of higher percentage concentrations of clay should be investigated further. LEACHW (the water regime submodel of LEACHM) was used to predict leachate discharge from the Coastal Park landfill, assuming a hypothetical capping system of 1 or 2 m soil depth with 0, 50, 70, or 90 % vegetation cover (Acacia cyclops), and based on the assumption that drainage from this layer into the waste pile contributes directly to leachate generation. The model predicted that under average rainfall conditions the landfill, with a 2 m soil depth and 0 % vegetation cover, would not generate leachate. However, under the wettest conditions not even a 90% vegetation cover and 2 m soil cover would be sufficient to prevent the landfill from generating leachate, suggesting that, under such conditions, a more effective leachate management strategy, such as leachate collection sumps, should be implemented. This exercise demonstrated the use of LEACHM as an alternative means of predicting leachate discharge from landfill sites.

No description available.

<p>By studying the boron isotope composition of marine carbonates, the effectiveness of the tracer to reconstruct the ancient seawater pH and, in turn, atmospheric pCO₂ can be assessed. The boron isotope-pH proxy relies on the hypothesis that only B(OH)₄^-, which has a known boron isotope composition with respect to pH, is incorporated into the carbonate crystal lattice. This research synthesized inorganic aragonite from a range of stable pH values to quantify the dependence of aragonite <em>δ</em>¹¹B on the pH of the precipitating solution. The increasing boron isotope composition of aragonite with increasing pH is consistent with sole incorporation of B(OH)₄^- into the carbonate. The sensitivity of the acid dissociation and isotope equilibrium constants make it difficult to confirm whether or not B(OH)₄^- is the only species contributing to the boron isotope composition of aragonite. The relationship between the boron isotope composition of marine carbonates and ocean pH has wide appeal and, if properly understood, could provide tremendous insight into the history of Earth’s climate.</p> <p>This research also evaluated carbon isotope fractionation between aragonite and dissolved inorganic carbon (DIC) in high ionic strength systems at 25 °C and found it to be consistent with carbon isotope fractionation in low ionic strength environments. The analysis of various isotopic compositions within this study led to the development of new methodology to simultaneously measure the oxygen isotopes of water and carbon isotopes of DIC from small solution samples using continuous flow isotope ratio mass spectrometry (CF-IRMS).</p> / Master of Science (MSc)