کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
9822525 | 1519145 | 2005 | 15 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Effects of the orientation of smectite particles and ionic strength on diffusion and activation enthalpies of Iâ and Cs+ ions in compacted smectite
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
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چکیده انگلیسی
The apparent diffusion coefficients (Da) for Iâ and Cs+ ions in compacted Na-smectite which is a major constituent clay mineral of bentonite were studied as a function of smectite's dry density (0.9-1.4 Mg/m3), ionic strength ([NaCl] = 0.01, 0.51 M), temperature (22-60 °C) and diffusion direction to the orientated direction of smectite particles. The Na-smectite was prepared by ion-exchanging with Na+ ions a Na-bentonite, Kunipia-F®, of which smectite content is over 99 wt.%. The Da-values for both ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a low-ionic strength of [NaCl] = 0.01 M. The Da-values for Iâ ions showed different trends depending on diffusion direction and dry density at a high-ionic strength of [NaCl] = 0.51 M. Namely, although the Da-values for Iâ ions showed a tendency to be higher in the parallel direction than in the perpendicular direction to the orientated direction of smectite particles at a high-dry density of 1.4 Mg/m3, these showed a reciprocal tendency at dry densities of 0.9-1.0 Mg/m3. The Da-values for Cs+ ions uniformly increased with an increase of ionic strength in both diffusion directions. Considering electrostatic effect from smectite surface and the change in tortuosity on dry density, ionic strength and diffusion direction to the orientated direction of smectite particles, Iâ ions are considered to mainly diffuse in interstitial pores. While, Cs+ ions can diffuse in both interlayer and interstitial pores, and the Da-values are considered to have elevated by competing with Na+ ions. The activation enthalpies (ÎEa) for Iâ ions, slightly higher (ÎEa = 19.8â20.0 kJ/mol) than that of the diffusion coefficient in free water (Do) for Iâ ions (ÎEa = 17.36 kJ/mol) at a low-ionic strength of [NaCl] = 0.01 M, decreased with an increase of ionic strength, became of similar level to that of the Do at a high-ionic strength of [NaCl] = 0.51 M, increased with an increase of dry density. On the contrary, the ÎEa-values for Cs+ ions, clearly higher (ÎEa = 25.6â28.4 kJ/mol) than that of the Do for Cs+ ions (ÎEa = 16.47 kJ/mol) even in low-dry density over the ionic strength, increased with an increase of dry density. The ÎEa-values for Cs+ ions are considered to be due to the decrease in the activity of porewater in addition to the effect of ion exchange enthalpy between Cs+ and Na+ ions in smectite.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Applied Clay Science - Volume 29, Issues 3â4, June 2005, Pages 267-281
Journal: Applied Clay Science - Volume 29, Issues 3â4, June 2005, Pages 267-281
نویسندگان
Haruo Sato,