scholarly journals An experimental investigation of the solubility and speciation of uranium in hydrothermal ore fluids

2021 ◽  
Author(s):  
K U Rempel ◽  
A E Williams-Jones ◽  
K Fuller
Keyword(s):  
Experimental Data ◽  
Genetic Model ◽  
Hydrothermal Solution ◽  
Ore Deposits ◽  
Common Belief ◽  
Alkaline Ph ◽  
Thermodynamic Constants ◽  
Few Data ◽  
Ppm Level ◽  
Uranium Species

Experimental data on the solubility and speciation of uranium in hydrothermal solution is required to improve genetic models for the formation of ore deposits, yet very few data of this type have been published. Of particular interest is the oxidation state of the uranium in solution, as conventional wisdom suggests that U is dissolved in the oxidized U(VI) state and precipitated as reduced U(IV) minerals, yet recent experiments have shown ppm-level solubility for U(IV). This study investigated the mobility of reduced U(IV) and oxidized U(VI) in acidic (pH = 2), fluoride- bearing and alkaline (pH = 10), chloride-bearing solutions at 100-200°C and 1 to 15.8 bars (0.1-1.58 MPa). Preliminary data for the mobility of U(IV) in pH 2 fluids with 0.01 m F- show concentrations of 1.76 to 3.92 ppm U at 200°C, indicating that, contrary to common belief, the reduced U(IV) can be transported in solution. We have also conducted experiments on U(VI) solubility in pH 2 fluoride-bearing, and pH 10 chloride-bearing solutions. Uranium concentrations in the F- -bearing experiments ranged from 624 to 1570 ppm (avg. 825 ppm, n = 6) at 100°C, 670 to 1560 ppm (avg. 931 ppm, n = 4) at 150°C, and 3180 to 7550 ppm (avg. 5240, n = 9) at 200°C. In comparison, U concentrations in the Cl- -bearing runs range from 86.1 to 357 ppm (avg. 185 ppm, n = 15) at 200°C. Clearly, oxidized U(VI) is very readily mobilized in hydrothermal fluids. However, the measured concentrations of U(VI) are independent of those of F- or Cl-, suggesting the formation of U oxide or hydroxide species rather than U chlorides or fluorides. These experimental data will be verified and supplemented in future experiments, which will be used to derive the stoichiometry and thermodynamic constants for the dominant uranium species in hydrothermal solutions. The data from this study will then be integrated into a comprehensive genetic model for uranium ore-forming systems.

scholarly journals Malfunction in GABA and Glutamate as Pathways to Depression: A Review of the Evidence

2009 ◽  
Vol 1 ◽  
pp. CMT.S3481 ◽  
Author(s):  
Christopher F Sharpley
Keyword(s):  
Experimental Data ◽  
Side Effects ◽  
Disease Burden ◽  
Potential Treatment ◽  
Pharmacological Treatments ◽  
Neurotransmitter Systems ◽  
Antidepressant Medications ◽  
Depressed Patients ◽  
Few Data

With nearly one fifth of the population experiencing depression sometime during their lives, plus the recent finding that depression rivals smoking in its association with mortality, the search for effective pharmacological treatments for depression remains urgent. However, despite this heavy disease burden upon society, the various waves of antidepressants developed in the last 40 years have shown significant side effects and little specific efficacy over placebo. One potential treatment may be via re-establishment of glutamate and GABA neurotransmitter systems that have been shown to malfunction in depressed patients. The literature describing possible causal links between GABA and/or glutamate malfunction and depression is reviewed, plus those studies which provide experimental data to confirm this hypothesis. While there is plausible support for the links between malfunction of these neurotransmitters and depression, few data exist yet regarding development of effective antidepressant medications based upon these findings.

scholarly journals Solubility equilibria and geochemical modeling in the field of radioactive waste disposal

2005 ◽  
Vol 77 (3) ◽  
pp. 631-641 ◽  
Author(s):  
W. Hummel
Keyword(s):  
Experimental Data ◽  
Review Process ◽  
Geochemical Modeling ◽  
Radioactive Waste Disposal ◽  
Strict Sense ◽  
Chemical Thermodynamic ◽  
Hydroxo Complexes ◽  
Thermodynamic Constants ◽  
Experimental Solubility Data ◽  
Chemical Knowledge

If a true thermodynamic equilibrium with a well-known solid is expected to establish, chemical equilibrium thermodynamics allows estimation of the maximum concentration of a given radionuclide in a specified pore fluid of an underground repository. However, in the course of the review process for the Nagra/PSI Chemical Thermodynamic Data Base 01/01, important cases of insufficient chemical knowledge were identified, leading to gaps in the database. First, experimental data for the ThO2–H2O and UO2–H2O systems cannot be interpreted by a unique set of thermodynamic constants. There, a pragmatic approach was chosen by including parameters in the database that are not thermodynamic constants in a strict sense, but that reproduced relevant experimental observations. Second, potentially important thermodynamic constants are missing because of insufficient experimental data. Estimations of these missing constants led to problem-specific database extensions. Especially constants for ternary mixed carbonato-hydroxo complexes of tetravalent actinides have been estimated by the “backdoor approach”, i.e., by adjusting thermodynamic constants to maximum feasible values that are still consistent with all available experimental solubility data.

scholarly journals CORRELATIONS IN MULTI-LOCUS GENETIC SYSTEMS: A MATHEMATICAL MODEL

Genetics ◽  
1974 ◽  
Vol 77 (3) ◽  
pp. 591-605
Author(s):  
C T Falk ◽  
H Falk
Keyword(s):  
Experimental Data ◽  
Mathematical Model ◽  
Linear Combination ◽  
Genetic Model ◽  
Theoretical Models ◽  
Spin Model ◽  
Entire System ◽  
Additional Experimental Data ◽  
Genetic Systems

ABSTRACT A spin model with parallels to a multi-locus genetic model is presented which makes it possible to calculate the correlation between allelic states at any two loci in a population at equilibrium. The main features are: (1) The decay of correlation with distance may be expressed essentially as a linear combination of two exponentials, one of which dominates when the two loci are sufficiently far apart. (2) The correlation between two loci a specified distance apart is increased as the number of loci in the entire system increases. The results are compared with those of other theoretical models and discussed in the light of available experimental data. Possible ways of generalizing the model are outlined. However, additional experimental data is clearly needed to indicate the genetic relevance of work of this nature.

scholarly journals GENETIC MODEL OF MUD VOLCANISM OF THE KERCH PENINSULA (SCIENTIFIC AND APPLIED ASPECTS)

2021 ◽  
Vol 14 (1) ◽  
pp. 57-74
Author(s):  
V.A. Nesterovskyi ◽  
N.O. Hryshchanko ◽  
M.A. Deiak
Keyword(s):  
Genetic Model ◽  
Thick Layer ◽  
Volcanic Eruptions ◽  
Ore Deposits ◽  
Geological History ◽  
Mud Volcanoes ◽  
Near Surface ◽  
Kerch Peninsula ◽  
Mud Volcanism ◽  
History Of

The work is devoted to the results of many years of research and observations of mud volcanoes on the Kerch Peninsula. It aims to reveal the most important factors and aspects related to their origin, activity and impact on the geological history of the region. About 50 fossil and modern mud volcanoes have been defined on the Kerch Peninsula and the adjacent part of the water area. Their activity is consistent with the phases of activation of the alpine tectogenesis of the Crimean-Caucasian segment and is intermittent and impulsive. In the geological history of the peninsula, four main bursts of mud volcanic activity are clearly recorded: in the Upper Maikop, Chokrak-Karagan, Sarmatian and Cimmerian. Its greatest activity is manifested in the late Miocene and early Pliocene. Favorable factors for the development of mud volcanoes within the peninsula are the presence of a thick layer of plastic clays enriched in water and gas fluids, the widespread development of brachyanticlinal folds in the Neogene structural surface and a network of deep faults and fractures. The activity of mud volcanoes is associated with the formation of specific compensation structures – depressed synclines, which have become widespread on the Kerch Peninsula. The latter, depending on the paleogeographic conditions (sea, land) and the structural position of volcanoes in the anticlines, have acquired different specifics of structure and filling. Some depressed synclines are associated with iron ore deposits, which differ from typical iron ores of the mulde type by significant capacity, structural and textural features and material composition. Components of hydrothermal and exogenous origin have been defined in the products of mud volcanism: mud gases, mud waters, mud breccias, which indicates the genetic connection of this phenomenon with deep and near-surface processes. In addition, liquid, solid and gaseous hydrocarbons are often detected in volcanic eruptions. The latter are a criterion for searching for oil and gas at depth. Mud volcanoes of the Kerch Peninsula are a unique testing ground for monitoring the processes of modern mineral formation, the dynamics of deep processes and seismic activity in the region.

The Kupferschiefer Cu–Ag ore deposits in Poland: a re-appraisal of the evidence of their origin and presentation of a new genetic model

1987 ◽  
Vol 24 (10) ◽  
pp. 2016-2037 ◽  
Author(s):  
E. Craig Jowett ◽  
Andrzej Rydzewsk ◽  
Robin J. Jowett
Keyword(s):  
Genetic Model ◽  
Volcanic Rocks ◽  
Ore Deposits ◽  
Sulphur Isotope ◽  
Chloride Complexes ◽  
Plan View ◽  
Stratiform Copper Deposits ◽  
Tethys Ocean ◽  
Calcite Cement ◽  
Copper Sulphides

The Kupferschiefer stratiform copper deposits in central Europe have long been considered a classic example of syngenetic mineralization. However, metal zoning and host-rock relationships determined during exploration around the recently discovered Lubin district orebodies in southwest Poland suggest that the ore may instead be late diagenetic. The mineralization occurs as thin, extensive blankets of sulphides in the pyritic, organic-rich basal units of the Late Permian Zechstein restricted marine sequence and in the eolian Weissliegendes sandstone at the top of the Early Permian Rotliegendes continental rift sequence of bimodal volcanic rocks and redbeds. It is directly underlain and controlled by irregular, oval zones of Rote Fäule (RF), a barren oxidized and reddened portion of the normally dark grey, pyritic basal Zechstein rocks. In plan view, the metals occur as successive belts enriched in copper (+ silver), lead, and zinc, which developed laterally from and encircle the RF zones. The ore transgresses the depositional strike of the basal Zechstein and can occur in any sedimetary facies. In section, the ore cuts across sedimentary layering from the Zechstein limestone down through the Kupferschiefer shale (Ks) into the sand stone below. Framboidal, presumably very early diagenetic, pyrite is the dominant sulphide above and lateral to the ore zones; over most of the basin, the Ks is pyritic and not anomalously high in metals compared with similar shale elsewhere. In the ore bodies, Cu, Ag, Pb, and Zn are significantly above the typical background contents, implying that these metals have been introduced. Metal contents in the RF are within the range of background contents of the Ks, suggesting that the metal source is external to the Ks. The RF–copper zones are coincident with underlying buried basement highs and occur only above Rotliegendes sediments with underlying volcanic rocks, indicating a possible genetic connection. The metal zones generally dip away from the highs toward the basin centres, suggesting convective, rather than throughgoing, fluid flow. Sulphides, as disseminations and streaks, commonly replace earlier calcite cement and lenses, lithic fragments, and quartz grains. Horizon tal and vertical dilatant veinlets of calcite and copper sulphides appear to have formed after lithification and contemporaneously with the disseminations and streaks, but not by remobilization of existing sulphides. The veinlet orientations are believed to be Kimmerian age (mid-Triassic to Late Jurassic), and the orebodies are cut and displaced, but not remobilized, by fractures and dikes of inferred Alpine (Cretaceous) age. Published sulphur-isotope ratios indicate that the copper sulphides were not formed in isotopic equilibrium with the pyrite, but adequate sulphur- and lead-isotope information on the ore deposits is not available to support an early or late diagenetic timing. The paleomagnetic age of the stable chemical remanence of the RF is Middle Triassic, supporting a late diagenetic origin of the ore coincident with a second rifting event. On account of these asso ciations and controls, it is proposed that the RF–ore systems were formed by converting Na–Ca–CI Rotliegendes formational brines. The metals were leached from the Rotliegendes volcanic detritus and carried in solution as chloride complexes through the redbeds up the flanks of the buried basement highs to the reduced pyritic Ks above. The fluids oxidized the original Ks pyrite to form the Rote Fäule, and the ore sulphides were precipitated on the far side of this subhorizontal oxidation–reduction front. This late diagenetic mineralizing event likely occurred during the Triassic, when rapid burial and increased heat flow, associated with the opening of the Tethys ocean to the south, generated natural gases and vertical fractures in the Ks and increased convective fluid velocities in the Rotliegendes basins.

Using UCODE_2005 and PHREEQC To Determine Thermodynamic Constants from Experimental Data

Ground Water ◽  
2007 ◽  
Vol 45 (3) ◽  
pp. 368-373 ◽  
Author(s):  
Magnus E. Skold ◽  
Geoffrey D. Thyne ◽  
John E. McCray
Keyword(s):  
Experimental Data ◽  
Thermodynamic Constants
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