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