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The dominating influence of calcium ...

Stanford University.

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The dominating influence of calcium on the biogeochemical fate of uranium.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	The dominating influence of calcium on the biogeochemical fate of uranium./
作者:	Stewart, Brandy D.
面頁冊數:	121 p.
附註:	Adviser: Scott Fendorf.
Contained By:	Dissertation Abstracts International69-05B.
標題:	Biogeochemistry. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3313670
ISBN:	9780549623366

The dominating influence of calcium on the biogeochemical fate of uranium.
Stewart, Brandy D.

The dominating influence of calcium on the biogeochemical fate of uranium. - 121 p.

Adviser: Scott Fendorf.

Thesis (Ph.D.)--Stanford University, 2008.

Uranium's radioactivity and metal toxicity render it a pollutant of concern to both human health and ecological systems. Inadequate disposal of uranium-laden waste from mining and nuclear enrichment processes has released substantial quantities of uranium into surface and subsurface environments, where uranium's redox state, particularly the proportion of U(VI) to U(IV), often governs its solubility and thus its potential for migration. The biogeochemical behavior of uranium in environmental settings, comprised of dissolved metals, organic ligands, and mineralogical matrices is complex and in many cases poorly understood. The potential for uranium transport in the subsurface is decreased in anaerobic conditions as compared to aerobic conditions, through the formation of the sparingly soluble UO2 phase. Additionally, uranium may adsorb on a variety of mineral surfaces decreasing its solution concentration. However, these processes are strongly impacted by the presence of dissolved calcium by inducing the formation of ternary uranyl-calcium-carbonato complexes. The research described in this thesis seeks to elucidate the impact of calcium on uranium biogeochemical cycling in surface and subsurface settings.

ISBN: 9780549623366Subjects--Topical Terms:

545717
Biogeochemistry.

The dominating influence of calcium on the biogeochemical fate of uranium.
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245 1 4 $a The dominating influence of calcium on the biogeochemical fate of uranium.
300 $a 121 p.
500 $a Adviser: Scott Fendorf.
500 $a Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 2859.
502 $a Thesis (Ph.D.)--Stanford University, 2008.
520 $a Uranium's radioactivity and metal toxicity render it a pollutant of concern to both human health and ecological systems. Inadequate disposal of uranium-laden waste from mining and nuclear enrichment processes has released substantial quantities of uranium into surface and subsurface environments, where uranium's redox state, particularly the proportion of U(VI) to U(IV), often governs its solubility and thus its potential for migration. The biogeochemical behavior of uranium in environmental settings, comprised of dissolved metals, organic ligands, and mineralogical matrices is complex and in many cases poorly understood. The potential for uranium transport in the subsurface is decreased in anaerobic conditions as compared to aerobic conditions, through the formation of the sparingly soluble UO2 phase. Additionally, uranium may adsorb on a variety of mineral surfaces decreasing its solution concentration. However, these processes are strongly impacted by the presence of dissolved calcium by inducing the formation of ternary uranyl-calcium-carbonato complexes. The research described in this thesis seeks to elucidate the impact of calcium on uranium biogeochemical cycling in surface and subsurface settings.
520 $a Chapters 2 quantifies the impact of varying Ca concentration on enzymatic U(VI) reduction rates in the presence of iron oxides which can serve as alternate, and in some cases competing electron acceptors for microbial uranium reduction. Chapter 3 explores this system in greater quantitative detail by providing a mathematical framework for simultaneous enzymatic reduction of iron and uranium in the presence of Ca. Chapters 4 and 5 explore the profound impact of Ca on uranium sorption processes. Adsorption to mineral surfaces in systems varying in dissolved and solid-phase Ca concentration is measured and the role of Ca is discussed. Finally, the potential for U(VI) incorporation into transforming Fe (hydr)oxides is explored and investigated under both reducing and oxidizing conditions.
520 $a The results of this research reveal that Ca has a startling impact on uranium's mobility in environmental systems through formation of ternary uranyl-calcium-carbonato complexes, decreasing both the extent and rate of U(VI) reduction and amount of U(VI) adsorption to mineral surfaces. First-order rate coefficients are more than an order of magnitude greater for reduction of UO2-CO 3 species than for Ca-UO2-CO3 species, demonstrating the resistance of the ternary complexes to reduction, likely through steric hinderances imposed by the ternary complexes. Additionally, soil-water partitioning coefficients decrease by more than 50% in the presence of 1 mM Ca and 3.8 mM carbonate, relative to systems with only carbonate on a variety of mineral surfaces. Despite decreased adsorption on iron-bearing minerals, U(VI) can be incorporated into transforming Fe (hydr)oxides, stable in the presence of molecular oxygen, with a resultant mass ratio of 4.5 mmol U per kg solid, in the presence of 3 mM Fe(II) with the ternary complexes dominating uranyl speciation. This research clearly demonstrates that the fate of uranium in natural systems is closely linked not only to anaerobic/aerobic conditions, but also to geochemical conditions controlling uranium speciation, and to the fate of iron.
520 $a In sum, the research presented in this thesis evaluates and quantifies the impact of dissolved Ca on the fate of uranium in complex biogeochemical systems and advances our knowledge of uranium's potential for mobility in surface and subsurface settings by describing and evaluating the partitioning of uranium on solid phases in these complex systems.
590 $a School code: 0212.
650 4 $a Biogeochemistry. $3 545717
650 4 $a Engineering, Environmental. $3 783782
650 4 $a Geochemistry. $3 539092
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710 2 $a Stanford University. $3 754827
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791 $a Ph.D.
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