1D Ion exchange#

Overview and Capabilities tested#

This test example performs the simulation of cation exchange on a single exchange site in a 1D flow domain, testing the following capabilities:

  • 1D flow

  • 1D advective transport

  • Geochemical reactions

    • Ion exchange (equilibrium)

For details on this test, see About.

Background#

Ion exchange description to come.

Model#

Flow and transport#

See the 1D Conservative tracer transport example.

Primary species#

Four primary species are used: 3 cations ( \(\ce{Na^+}\) , \(\ce{Ca^{2+}}\) , \(\ce{Mg^{2+}}\) ) and 1 anion ( \(\ce{Cl^-}\) ) to charge-balance the solution.

Ion exchange#

\(\ce{Na^+}\) , \(\ce{Ca^{2+}}\) , \(\ce{Mg^{2+}}\) exchange on the single bulk site \(\ce{X^-}\) . The three equilbrium exchange reactions are (by convention, secondary species are given in the left hand side, while primary species are in the right hand side):

  • \(\ce{NaX} = \ce{Na^+} + \ce{X^-}\), \(\text{ } \log(K)=1.0\)

  • \(\ce{CaX_2} = \ce{Ca^{2+}} + 2 \ce{X^-}\), \(\text{ } \log(K)=0.2953\)

  • \(\ce{MgX_2} = \ce{Mg^{2+}} + 2 \ce{X^-}\), \(\text{ } \log(K)=0.1666\)

Problem specifications#

Flow and transport#

See the 1D Conservative tracer transport example. The simulation is run to 50 years.

Geochemistry#

The cation exchange capacity (CEC) of the bulk site is 750.0 \(\text{ eq/m}^3\).

Results and Comparison#

Expected results#

Expected results to come.

Simulation results#

The figure below shows both the aqueous and sorbed concentrations of \(\ce{Na^+}, \ce{Ca^+}, \ce{Mg^{2+}}, \ce{Cl^-}\) along the flow direction at 50 years.

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

../../../_images/ion_exchange_1d.png

About#

  • Benchmark simulator: PFlotran

  • Files:

    • Amanzi input file/s (native chemistry): amanzi-u-1d-ion-exchange.xml

    • Amanzi input file/s (Alquimia chemistry): amanzi-1d-ion-exchange-alq.xml, 1d-ion-exchange.in, ion-exchange.dat

    • Benchmark simulator input file: 1d-ion-exchange.in, ion-exchange.dat

  • Location: testing/benchmarking/chemistry/ion_exchange_1d

  • Author: B. Andre, G. Hammond

  • Testing and Documentation: S. Molins

  • Last tested on Oct 4, 2013