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