کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
8910832 | 1637931 | 2018 | 33 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Experimental investigation of nitrogen isotopic effects associated with ammonia degassing at 0-70â¯Â°C
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موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
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چکیده انگلیسی
Ammonia degassing is a common process in natural alkaline waters and in the atmosphere. To quantitatively assess the nitrogen cycle in these systems, the essential parameter of nitrogen isotope fractionation factors associated with ammonia degassing is required, but still not constrained yet. In this study, we carried out laboratory experiments to examine the nitrogen isotope behavior during ammonia degassing in alkaline conditions. The experiments started with ammonium sulfate solution with excess sodium hydroxide. The reaction can be described as: NH4+â¯+â¯OHâ (excess)â¯ââ¯NH3·nH2Oâ¯ââ¯NH3 (g)â. Two sets of experiments, one with ammonia degassing under static conditions and the other with ammonia degassing by bubbling of N2 gas, were carried out at 2, 21, 50, and 70â¯Â°C. The results indicate that kinetic isotopic effects are dominated during efficient degassing of ammonia in the bubbling experiments, which yielded kinetic nitrogen isotope fractionation factors αNH3(g)-NH3(aq) of 0.9898 at 2â¯Â°C, 0.9918 at 21â¯Â°C, 0.9935 at 50â¯Â°C and 0.9948 at 70â¯Â°C. These values show a good relationship with temperature as 103lnαNH3(g)-NH3(aq)â¯=â¯14.6â¯ââ¯6.8â¯Ãâ¯1000/T. In contrast, isotopic effects during less efficient degassing of ammonia in the static experiments are more complicated. The results do not match either kinetic isotope fractionation or equilibrium isotope fractionation but sit between these two. The most likely cause is that back dissolution of the degassed ammonia occurred in these experiments and consequently shifted kinetic isotope fractionation toward equilibrium isotope fractionation. Our experimental results highlight complicated isotopic effects may occur in natural environments, and need to be fully considered in the interpretation of field data.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Geochimica et Cosmochimica Acta - Volume 226, 1 April 2018, Pages 182-191
Journal: Geochimica et Cosmochimica Acta - Volume 226, 1 April 2018, Pages 182-191
نویسندگان
Yuying Deng, Yingzhou Li, Long Li,