Kinetics and Mechanism of Trithionate and Tetrathionate Oxidation at Low pH by Hydroxyl Radicals     

Gregory K. Druschel  Robert J. Hamers  George W. Luther III  Jillian F. Banfield 《Aquatic Geochemistry》2003,9(2):145-164

The oxidation kinetics of trithionate (S₃O₆^2- ) and tetrathionate (S₄O ₆ ^2- ) with hydroxyl radicals (OH^*) have been investigated in systems analogous to acid mine drainage (AMD) environments. The discovery of hydroxyl radical (OH^*) formation on pyrite surfaces (Borda et al., 2003) suggests hydroxyl radicals may affect the oxidation kinetics of intermediate sulfur species such as tetrathionate. Cyclic voltammetry experiments in acidic solutions indicate that the reaction of S₄O ₆ ^2- with OH^* goes through an unknown intermediate, tentatively assigned as S₃O ₄ ^n- . An outer-sphere electron transfer mechanism for the reaction of S₄O ₆ ^2- with OH^* to form S₃O ₄ ^n- is proposed based on experimental results. Oxidation rates for trithionate and tetrathionate in the presence of Fenton's reagent (which forms hydroxyl radicals) are too fast to be directly measured using UV-Vis spectrophotometry, electrochemical, or stop-flow spectrophotometry methods. Competitive reaction kinetics within the context of the Haber—Weiss mechanism suggests that the rate constant for the oxidation of trithionate and tetrathionate with OH^* is in excess of 10⁸ M^-1 sec^-1.  相似文献   

Inelastic models of lithospheric stress-I. Theory and application to outer-rise plate deformation     

Steve Mueller  George L. Choy  William Spence 《Geophysical Journal International》1996,125(1):39-53

  相似文献   

Inelastic models of lithospheric stress-11. Implications for outer-rise seismicity and dynamics     

Steve Mueller  William Spence  George L. Choy 《Geophysical Journal International》1996,125(1):54-72

  相似文献   

410 km discontinuity sharpness and the form of the olivine α-β phase diagram: resolution of apparent seismic contradictions     

George R. Helffrich  Bernard J. Wood 《Geophysical Journal International》1996,126(2):F7-F12

  相似文献   

Geomorphological studies in Southern Africa: G.F. Dardis and B.P. Moon (Editors). A.A. Balkema, Rotterdam, 1988, x + 509 pp., 222 figures (including 105 half-tone photos) and 31 tables. Price: US$60.00 hardback. ISBN 90-6191-831-6     

George A. Brook 《Geomorphology》1996,16(4):349-350

  相似文献   

Dynamic stochastic estimation of physical variables   总被引：1，自引：0，他引：1  

George Christakos  Vijayanivas R. Raghu 《Mathematical Geology》1996,28(3):341-365

A fundamental problem facing the physical sciences today is analysis of natural variations and mapping of spatiotemporal processes. Detailed maps describing the space/time distribution of groundwater contaminants, atmospheric pollutant deposition processes, rainfall intensity variables, external intermittency functions, etc. are tools whose importance in practical applications cannot be overestimated. Such maps are valuable inputs for numerous applications including, for example, solute transport, storm modeling, turbulent-nonturbulent flow characterization, weather prediction, and human exposure to hazardous substances. The approach considered here uses the spatiotemporal random field theory to study natural space/time variations and derive dynamic stochastic estimates of physical variables. The random field model is constructed in a space/time continuum that explicitly involves both spatial and temporal aspects and provides a rigorous representation of spatiotemporal variabilities and uncertainties. This has considerable advantages as regards analytical investigations of natural processes. The model is used to study natural space/time variations of springwater calcium ion data from the Dyle River catchment area, Belgium. This dataset is characterized by a spatially nonhomogeneous and temporally nonstationary variability that is quantified by random field parameters, such as orders of space/time continuity and random field increments. A rich class of covariance models is determined from the properties of the random field increments. The analysis leads to maps of continuity orders and covariances reflecting space/time calcium ion correlations and trends. Calcium ion estimates and the associated statistical errors are calculated at unmeasured locations/instants over the Dyle region using a space/time kriging algorithm. In practice, the interpretation of the results of the dynamic stochastic analysis should take into consideration the scale effects.  相似文献   

Porewater pressure increases in soil and rock from underground chemical and nuclear explosions   总被引：3，自引：0，他引：3  

Wayne A. Charlie  George E. Veyera  Deanna S. Durnford  Donald O. Doehring 《Engineering Geology》1996,43(4):225-236

A review and analysis of chemical and nuclear explosive-induced porewater pressure increases and induced rise in groundwater table elevations (groundwater mounding) is presented. Our analysis indicates that residual pore pressure increases and groundwater mounding can be induced by underground chemical and nuclear explosions to scaled distances of 879 m/(kt)^1/3. This relationship is linear over seven orders of magnitude of explosive energy ranging from a 0.01 kg chemical explosion to a 100 kt nuclear explosion and is valid for a wide variety of saturated geological profiles. Underground chemical explosions, and probably underground nuclear explosions have the potential to induce liquefaction of water-saturated soils to scaled distances of about 260 m/(kt)^1/3.  相似文献   

Lake Koronia, Greece: Shift from autotrophy to heterotrophy with cultural eutrophication and progressive water-level reduction     

Chrysoula Mitraki  Thomas L. Crisman  George Zalidis 《Limnologica》2004,34(1-2):110

Lake Koronia, a Ramsar site, is shallow, polymictic, hypertrophic and until recently was aerially the fourth largest lake in Greece. Although exceeding 5 m in the past, lake depth has declined progressively from 3.8 m in 1980 to < 1 m in 1997, reducing surface area and water volume by 50% and 80%, respectively. Specific conductivityincreased from 1300 μS cm⁻¹ in 1977 to >6000 μS cm⁻¹ in 1991. Increased phosphate concentrations from the late 1970's (8–45 μg L⁻¹) to the late 1990's (100–1000 μg L⁻¹) document that the previously eutrophic system with a limited littoral zone switched to hypertrophy dominated by massive cyanobacteria blooms. Oxygen saturation of the water column increased progressively from about 80% in 1983 to full saturation about 1993, after which it decreased progressively to only 20% saturation in 1997. In spite of cyanobacteria dominance, community metabolism of the lake switched from progressively increasing autotrophy to rapidly advancing heterotrophy associated with progressive water-level reduction leading to fish extirpation in the lake.  相似文献   

Nature of polymerization and properties of silicate melts and glasses at high pressure     

Sung Keun Lee  George D. Cody  Bjorn O. Mysen 《Geochimica et cosmochimica acta》2004,68(20):4189-4200

The structures of sodium silicate and aluminosilicate glasses quenched from melts at high pressure (6-10 GPa) with varying degrees of polymerization (fractions of nonbridging oxygen) were explored using solid-state NMR [¹⁷O and ²⁷Al triple-quantum magic-angle spinning (3QMAS) NMR]. The bond connectivity in melts among four and highly coordinated network polyhedra, such as ^[4]Al, ^[5,6]Al, ^[4]Si, and ^[5,6]Si, at high pressure is shown to be significantly different from that at ambient pressure. In particular, in the silicate and aluminosilicate melts, the proportion of nonbridging oxygen (NBO) generally decreases with increasing pressure, leading to the formation of new oxygen clusters that include 5- and 6-coordinated Si and Al in addition to 4-coordinated Al and Si, such as ^[4]Si-O-^[5,6]Si, ^[4]Si-O-^[5,6]Al and Na-O-^[5,6]Si. While the fractions of ^[5,6]Al increase with pressure, the magnitude of this increase diminishes with increasing degrees of ambient-pressure polymerization under isobaric conditions. Incorporating the above structural information into models of melt properties reproduces the anomalous pressure-dependence of O²⁻ diffusivity and viscosity often observed in silicate melts.  相似文献   

Torngat ultramafic lamprophyres and their relation to the North Atlantic Alkaline Province   总被引：3，自引：0，他引：3  

Sebastian Tappe  George A. Jenner  Stephen F. Foley  Larry Heaman  Dean Besserer  Bruce A. Kjarsgaard  Bruce Ryan 《Lithos》2004,76(1-4):491-518

Geological mapping and diamond exploration in northern Quebec and Labrador has revealed an undeformed ultramafic dyke swarm in the northern Torngat Mountains. The dyke rocks are dominated by an olivine-phlogopite mineralogy and contain varying amounts of primary carbonate. Their mineralogy, mineral compositional trends and the presence of typomorphic minerals (e.g. kimzeyitic garnet), indicate that these dykes comprise an ultramafic lamprophyre suite grading into carbonatite. Recognized rock varieties are aillikite, mela-aillikite and subordinate carbonatite. Carbonatite and aillikite have in common high carbonate content and a lack of clinopyroxene. In contrast, mela-aillikites are richer in mafic silicate minerals, in particular clinopyroxene and amphibole, and contain only small amounts of primary carbonate. The modal mineralogy and textures of the dyke varieties are gradational, indicating that they represent end-members in a compositional continuum.

The Torngat ultramafic lamprophyres are characterized by high but variable MgO (10–25 wt.%), CaO (5–20 wt.%), TiO₂ (3–10 wt.%) and K₂O (1–4 wt.%), but low SiO₂ (22–37 wt.%) and Al₂O₃ (2–6 wt.%). Higher SiO₂, Al₂O₃, Na₂O and lower CO₂ content distinguish the mela-aillikites from the aillikites. Whereas the bulk rock major and trace element concentrations of the aillikites and mela-aillikites overlap, there is no fractional crystallization relation between them. The major and trace element characteristics imply related parental magmas, with minor olivine and Cr-spinel fractionation accounting for intra-group variation.

The Torngat ultramafic lamprophyres have a Neoproterozoic age and are spatially and compositionally closely related with the Neoproterozoic ultramafic lamprophyres from central West Greenland. Ultramafic potassic-to-carbonatitic magmatism occurred in both eastern Laurentia and western Baltica during the Late Neoproterozoic. It can be inferred from the emplacement ages of the alkaline complexes and timing of Late Proterozoic processes in the North Atlantic region that this volatile-rich, deep-seated igneous activity was a distal effect of the breakup of Rodinia. This occurred during and/or after the rift-to-drift transition that led to the opening of the Iapetus Ocean.  相似文献