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ION_EXCHANGE_RXN

Specifies parameters for an ion exchange reaction.

Required Cards:

ION_EXCHANGE_RXN

Opens the block.

CEC <float>

Cation exchange capacity in (1) equivalents per volume of mineral [eq/m³_mineral] (if a MINERAL card is present) or (2) equivalents per bulk volume [eq/m³_bulk] (if a MINERAL card is not present)

CATIONS

Opens the CATIONS block for listing cations participating in the reaction.

<Cation species Name> <float> <REFERENCE for reference cation only>

Name of cation and associated selectivity coefficient. One must select a reference cation with a selectivity coefficient of 1 and convert all the selectivity coefficients to be relative to the reference species selectivity coefficient. The REFERENCE card must be appended to the reference cation (see examples). The entered value is the half-reaction coefficient \(k\), not \(\log_{10} k\) and not \(1/k\). For a monovalent reference cation, \(k_i = K_{i,\mathrm{ref}}\). If a published selectivity is the per-equivalent coefficient \(\tilde K\), enter \(k_i = (\tilde K)^{z_i}\) when the reference valence is 1.

Optional Cards

MINERAL <string>

Name of the mineral to which the cations sorb.

Examples

For a complete soil-column transport example based on the experiments of Voegelin et al. (2000), see the Ion Exchange benchmark.

SORPTION
  ION_EXCHANGE_RXN
    MINERAL Halite
    CEC 750.  ! eq/m^3
    CATIONS
      Na+   1.d0 REFERENCE
      Ca++  3.38638672536d0  ! (1.84)^2
      Mg++  6.00240096038d0  ! (2.45)^2
    /
  /
END