Yazar "Cetiner, Ziya S." seçeneğine göre listele

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    Chemical controls on the solubility, speciation and mobility of lanthanum at near surface conditions: A geochemical modeling study
    (Pergamon-Elsevier Science Ltd, 2008) Cetiner, Ziya S.; Xiong, Yongliang
    Recent experimental determinations of the solubility products of common rare earth minerals Such as monazite and xenotime and stability constants for chloride, sulfate, carbonate and hydroxide complexes provide a basis to model quantitatively the solubility, and therefore the mobility, of rare earth elements (REE) at near surface conditions. Data on the mobility of REE and stabilities of REE complexes at near-neutral conditions are of importance to safe nuclear waste disposal, and environmental monitoring. The aim of this study is to understand REE speciation and Solubility of a given REE in natural environments. In this study, a series of formation constants for La aqueous complexes are recommended by using the specific interaction theory (SIT) for extrapolation to infinite dilution. Then, a thermodynamic model has been employed for calculation of the solubility and speciation of La in soil solutions reacted with the La end-member of mineral monazite (LaPO4), and other La-bearing solid phases including amorphous lanthanum hydroxide (La(OH)3, am) and different La carbonates, as a function of various inorganic and organic ligand concentrations. Calculations were carried out at near-neutral pH (pH 5.5-8.5) and 25 degrees C at atmospheric CO2 partial pressure. The model takes account of the species : La3+, LACl(2+), LaCl2+, LaCl30, LaCl4-, LaSO4+, La(SO4)(2)(-), LaCO3+, La(CO3)(2)(-), LaHCO32+, La(OH)(2+), LaOx(+), La(Ox)(2)(-), LaAc2+ and La(Ac)(2)(-) (where Ox(2-) = oxalate and Ac- = acetate). The calculations indicate that the La species that dominate at pH 5.5-8.5 in the baseline model soil solution (BMSS) include La3+, Laox(+), LaSO4+, LaCO3+ and La(CO3)(2)(-) in order of increasing importance as pH rises. The Solubility ofnionazite in the BMSS remains less than similar to 3 x 10(-9) M, exhibiting a minimum of similar to 2 x 10(-1)2 M at pH 7.5. The calculations quantitatively demonstrate that the concentrations of La controlled by the solubility of other La-bearing solid phases are many orders of magnitude higher than those controlled by monazite in the pH range from 5.5 to 8.5, suggesting that monazite is likely to be the Solubility-controlling phase at this pH range. The calculations also suggest that significant mobility of La (and other REE) is unlikely because high water-rock ratios on the order of at least 104 (mass ratio) are required to move 50% of the La from a soil. An increase in concentration of oxalate by one order of magnitude from that of the baseline model solution results in the dominance of LaOx(+) at pH 5.5-7.5. Similarly, the increase in concentration of SO42- by one order of magnitude makes LaSO4+ the dominant species at pH 5.5-7.5. Above pH 7.5, carbonate complexes are important. The increase in oxalate or SO42- concentrations by one order of magnitude can enhance the solubility of monazite by a factor of up to about 6 below neutral pH, in comparison with that in the baseline model soil solution. From pH 7.0 to 8.5, the solubility of monazite in the soil solutions with higher concentrations of oxalate or SO42- is similar, or almost identical, to that in the BMSS. (c) 2008 Elsevier Ltd. All rights reserved.
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    Comparative review of CGS and EGS in energy and environmental scope
    (Amer Chemical Soc, 2013) Cetiner, Ziya S.; Uyusur, Burcu; Ozsu, Eren; Karaca, Zeki; Sanliyuksel, Deniz
    [Anstract Not Available]
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    Experimental investigation of cesium mobility in the course of secondary mineral formations in Hanford sediment columns at 50°C
    (Springer, 2010) Mashal, Kholoud Y.; Cetiner, Ziya S.
    Formation of secondary minerals and Cs mobility in Hanford sediments were investigated under conditions similar to the Hanford tank leak in a dynamic flow system at 50A degrees C. The objectives were to (1) examine the nature and locations of secondary mineral phases precipitated in the sediments and (2) quantify the amount of Cs retained by the sediment matrix at 50A degrees C. To this end, Hanford sediments were packed into 10-cm long columns and leached with simulated tank waste consisting of 1.4 M NaOH, 0.125 M NaAlO2, 3.7 M NaNO3, and 1.3 x 10 (-aEuro parts per thousand 4) M Cs at 50A degrees C. Compositions of outflow solution were monitored with time for up to 25 days, and the columns were then segmented into four 2.5-cm long layers. The colloidal fraction in these segments was characterized in terms of mineralogy, particle morphology, Cs content, and short-range Al and Si structure. It was observed that cancrinite and sodalite precipitated at 50A degrees C. Approximately 53% Cs was retained in the column treated by the simulated tank waste at this temperature. Cesium retention in the column was lowered in the high ionic strength solution due to competition from Na for the exchange sites. This can be explained by alteration of distribution and number of sorption sites which reduces the selectivity of Cs for Na, and through the formation of cancrinite and sodalite. The formation of hydroxide complexes in highly alkaline solutions could also contribute to relatively poor retention of Cs by hindering ion exchange mechanism.
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    Initial assessment of hydrous Thorium(IV) solubility and speciation in geological environments: An experimental approach in presence of organic ligands
    (Asian Journal Of Chemistry, 2007) Cetiner, Ziya S.
    Data on the hydrolysis of Thorium(IV) and solubility of ThO2 in presence of organic ligands are of critical importance to the safe disposal and treatment of high-level nuclear waste. Such data are required to predict reliably thorium behaviour in high-level waste repositories where organic anions may be present. In addition, Th(IV) is considered to be a chemical analogue of tetravalent actinides such as Pu(IV). To establish the effect of pH and organic ligands on the hydrolysis of Th(IV), experiments on the solubility of hydrous ThO2 in aqueous solution at room temperature were performed, covering a wide range of pH (pH = 3-12) in 0.1 molal NaNO3 solutions. Experiments also were conducted in the presence of citrate, oxalate and EDTA with a concentration range of 100-500 mu mol. The solubility of ThO2 decreases with increase of pH (pH 3 to 6) and remains near the detection limit of ICP-MS (10(-9)-10(-10) M) in the range pH 6-12. These values are in accordance with data in the literature. The solubility of ThO2 does-not appear to be a sensitive function of the concentration of the investigated organic ligands at any given pH providing the fact that bulk of organic ligands is potentially absorbed by ThO2 solid phase. Thorium concentrations obtained from unfiltered and filtered samples showed almost an order of magnitude variation in molal concentration indicating a significant amount of colloid formation.
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    The influence of pH and temperature on the aqueous geochemistry of neodymium in near surface conditions
    (Springer, 2009) Cetiner, Ziya S.
    Geochemical calculations were employed for the solubility and speciation of neodymium in a model soil solution as a function of pH. The calculations were based on the recently determined stability constants for Nd and solubility product for the Nd end-member of mineral monazite (NdPO4). Simulations were carried out at near neutral pH (pH 6.0 to pH 7.5) and 25A degrees C at the atmospheric CO2 partial pressure. Additional calculations were also performed to assess Nd mobility at the extreme temperature conditions (300A degrees C) at neutral pH. Our results suggest that relatively dilute (Ionic Strength, I = 0.1), low-temperature waters may transport very small quantities of rare earth elements and actinides to the surficial environment at near neutral pH conditions. Evidently, higher temperature or extreme fluid composition may have a greater potential for mobilization of these elements. The results are pertinent to researchers interested in engineering applications for the precipitation of Nd and surrogate actinides from aqueous nuclear wastes.
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    Toward utilising geothermal waters for cleaner and sustainable production: potential of Li recovery from geothermal brines in Turkey
    (Inderscience Enterprises Ltd, 2015) Cetiner, Ziya S.; Dogan, Ozgur; Ozdilek, Goksel; Erdogan, Pembe Ozer
    Geothermal fluids are potentially significant sources of technology critical minerals and metals. These fluids can be processed to recover valuable metals such as gold, silver, zinc, and lithium. Interest and demand in lithium (Li) sources have increased in recent years. This is, in part, due to the wide applications of Li and its compounds in high-energy storage Li batteries, and in other technological fields, e.g., nuclear energy systems. Moreover, the costs associated with resource extraction from geothermal fluids are believed to be relatively low, and therefore many possible recovery techniques have been suggested. Lithium is one of the metals that dominate Na-Cl type of geothermal fluids in Turkey with its potential value. This article presents lithium concentrations of selected geothermal waters in Turkey and compares different methods that can be used to recover Li from them. Specifically, three methods will be discussed including direct precipitation as Li salts, separation by membrane filter and captured form through ion exchange resins.