Fluorite dissolution at acidic pH: In situ AFM and ex situ VSI experiments and Monte Carlo simulations

被引:33
作者
Cama, Jordi [1 ]
Zhang, Li [2 ]
Soler, Josep M. [1 ]
De Giudici, Giovanni [3 ]
Arvidson, Rolf S. [4 ,5 ]
Luttge, Andreas [4 ,5 ]
机构
[1] CSIC, Dept Geosci, Inst Environm Assessment & Water Res, IDAEA, ES-08034 Barcelona, Catalonia, Spain
[2] Univ So Calif, Dept Earth Sci, Los Angeles, CA 90089 USA
[3] Univ Cagliari, Dept Earth Sci, I-09127 Cagliari, Sardinia, Italy
[4] Rice Univ, Dept Earth Sci, Houston, TX 77005 USA
[5] Rice Univ, Dept Chem, Ctr Biol & Environm Nanotechnol, Houston, TX 77005 USA
关键词
MINERAL DISSOLUTION; CALCITE DISSOLUTION; FORCE MICROSCOPY; SURFACE REACTIVITY; KINETICS; RATES; EQUILIBRIUM; INHIBITION; CARBONATE; DISTANCE;
D O I
10.1016/j.gca.2010.04.067
中图分类号
P3 [地球物理学]; P59 [地球化学];
学科分类号
0708 ; 070902 ;
摘要
Dissolution of the fluorite (111) cleavage surface was investigated by means of in situ atomic force microscopy (AFM) and ex situ vertical scanning interferometry (VSI) experiments at pH range 1-3 in HCl solutions. Surface retreat was quantified at different pH values, yielding dissolution rates that were used to derive an empirical rate law for fluorite dissolution: Rate(fluorite)(mol m(-2) s(-1)) = 2.0 +/- 0.4 x 10(-6) . (a(H+))(0.38 +/- 0.07) where a(H+) is the proton activity. The influence of Delta G on fluorite dissolution rate at pH 2 was investigated by means of AFM and VSI surface measurements and flow-through experiments with powdered fluorite. The fluorite dissolution rate decreases non-linearly with increasing Gibbs energy (Delta G) and a dissolution plateau is obtained at Delta G <= -7 kcal mol(-1). This Delta G effect can be expressed with a rate law of the form Rate(fluorite) (mol m(-2) s(-1)) = k . a(H+)(n)(1 - exp(-4.7 x 10(-2) . (vertical bar Delta G vertical bar/RT)(1.41 +/- 0.24))) An alternative form based on a formulation making use of a Temkin number is also possible Rate(fluorite) (mol m(-2) s(-1)) = k . a(H+)(n) [1 - exp (Delta G/8RT)] Dissolution proceeds by formation of equilateral triangular etch pits with trigonal pyramidal morphology and emanation of stepwaves that are responsible for the surface retreat. The results of Monte Carlo simulations are consistent with this reaction mechanism. (C) 2010 Elsevier Ltd. All rights reserved.
引用
收藏
页码:4298 / 4311
页数:14
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