Partition coefficients of Ra and Ba in calcite

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Homogeneous partition coefficients (<i>D</i>) for Ra and Ba in calcite were determined from coprecipitation experiments using the Continuous Addition Method (CAM). The <i>D</i>-values derived for Ra and Ba are: <i>D</i><sub>Ra</sub> = (1.5 ±0.6) ×10<sup>-1</sup> and <i>D</i><sub>Ba</sub> = (1.6 ±1.1) ×10<sup>-2</sup>. Although these data were derived at low precipitation rates (<i>R</i>) for calcite (<i>R</i> < 9 nmol mg<sup>-1</sup>min<sup>-1</sup>), the solutions were significantly oversaturated in calcite. Values of <i>D</i> should, ideally, be derived at equilibrium and hence the effect of oversaturation should be examined. Therefore, a coprecipitation experiment using the Free Drift Method (FDM) with slow degassing was also carried out. This experiment occurs under conditions that are only slightly oversaturated and the rate of coprecipitation was confirmed to be slow compared to dissolution and precipitation at the calcite surface. The resultant heterogeneous partition coefficients showed good agreement with homogeneous partition coefficients derived by CAM. This indicates that the oversaturation in CAM did not affect partitioning of these metals in calcite and that the derived <i>D</i>-values represented equilibrium partitioning between the solution and the solid phase. The derived value of <i>D</i><sub>Ra</sub> is one order of magnitude larger than that of <i>D</i><sub>Ba</sub> despite the larger ionic radius of Ra. This indicates that compatibility of ionic radius is not a dominant parameter for preferential incorporation of Ra and Ba in calcite.

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  • Geochemical journal : journal of the Geochemical Society of Japan  

    Geochemical journal : journal of the Geochemical Society of Japan 42(3), 295-304, 2008-06-01 

    GEOCHEMICAL SOCIETY OF JAPAN

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各種コード

  • NII論文ID(NAID)
    10021093705
  • NII書誌ID(NCID)
    AA00654975
  • 本文言語コード
    ENG
  • 資料種別
    ART
  • ISSN
    00167002
  • NDL 記事登録ID
    9556370
  • NDL 雑誌分類
    ZM41(科学技術--地球科学)
  • NDL 請求記号
    Z53-R488
  • データ提供元
    CJP書誌  NDL  J-STAGE 
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