1D Surface complexation#

Overview and Capabilities tested#

This test example performs the simulation of \(\ce{Zn^{2+}}\) surface complexation on weak and strong iron hydroxide sites in a 1D flow domain.

  • 1D flow

  • 1D advective transport

  • Geochemical reactions

    • Aqueous complexation reactions (equilibrium)

    • Surface complexation reactions (equilibrium)

For details on this test, see About.

Background#

Introduction#

Description of surface complexation… The simulation is run to 50 years.

Model#

Flow and transport#

See the 1D Conservative tracer transport example.

Aqueous complexation#

Five equilibrium reactions are considered in aqueous phase that include the aqueous speciation of \(\ce{Zn^{2+}}\) (by convention, secondary species are given in the left hand side, while primary species are in the right hand side):

  • \(\ce{OH^- <=> H_2O - H^+}\), \(\; log(K)=13.9951\)

  • \(\ce{Zn(OH)_{2(aq)} <=> 2 H_2O - 2 H^+ + Zn^{2+}}\), \(\; log(K)=17.3282\)

  • \(\ce{Zn(OH)_3^- <=> 3 H_2O - 3 H^+ + Zn^{2+}}\), \(\; log(K)=28.8369\)

  • \(\ce{Zn(OH)_4^{2-} <=> 4 H_2O - 4 H^+ + Zn^{2+}}\), \(\; log(K)=41.6052\)

  • \(\ce{ZnOH^+ = H_2O -1 H^+ + 1 Zn^{2+}}\), \(\; log(K)=8.96\)

Surface complexation#

Two distinct iron hydroxide (\(\ce{FeOH}\)) surface sites are available for sorption of \(\ce{Zn^{2+}}\): weak \(\ce{({>}FeOH_{w})}\) and strong \(\ce{({>}FeOH_{s})}\). Surface site concentrations for \(\ce{>FeOH_{w}}\) and \(\ce{>FeOH_{s}}\) are defined in ‘Material Properties’. No explicit definition of the mineral phase on which \(\ce{Zn^{2+}}\) is required.

In total, six surface complexation reactions are considered:

  • \(\ce{{>}FeOH_{2w}^+ <=> {>}FeOH_{w} + H^+}\), \(\; log(K)=-7.18\)

  • \(\ce{{>}FeO^{-}_{w} <=> {>}FeOH_{w} - H^+}\), \(\; log(K)=8.82\)

  • \(\ce{{>}FeOHZn^{+}_{w} <=> {>}FeOH_{w} - H^+ + Zn^{2+}}\), \(\; log(K)=2.32\)

  • \(\ce{{>}FeOH_{2s}^+ <=> {>}FeOH_{s} + H^+}\), \(\; log(K)=-7.18\)

  • \(\ce{{>}FeO^{-}_{s} <=> {>}FeOH_{s} - H^+}\), \(\; log(K)=8.82\)

  • \(\ce{{>}FeOHZn^{+}_{s} <=> {>}FeOH_{s} - H^+}\) \(\; log(K)=-0.66\)

Problem Specification#

Flow and transport#

See the 1D Conservative tracer transport example.

Geochemistry#

To do.

Results and Comparison#

Expected results#

These are the expected results.

Simulation results#

(Source code, png, hires.png, pdf)

../../../_images/surface_complexation_1d.png

About#

  • Benchmark simulator: PFlotran

  • Files:

    • Amanzi input file: amanzi-u-1d-surface-complexation.xml

    • Benchmark simulator input file: 1d-surface-complexation.in

  • Location: amanzi/examples/examples/phase2/chemistry/1d-surface-complexation

  • Author: B. Andre, G. Hammond

  • Testing and Documentation: S. Molins

  • Last tested on Aug 31 2013