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MINERAL_KINETICS

Specifies coefficients for kinetic mineral precipitation-dissolution reactions. The rate law is defined through transition state theory, as detailed in section Mineral Precipitation and Dissolution of the theory guide. The reaction rate \(I_m\) for the \(m\) th mineral is defined as

(1)\[I_m = -a_m\Big(\sum_l k_{ml}(T) {\mathcal P}_{ml}\Big) \Big|1-\big(K_m Q_m\big)^{\left(\frac{1}{\lambda_m\sigma_m}\right)}\Big|^{\beta_m} {\rm sign}(1-K_mQ_m),\]

where a positive value corresponds to precipitation and a negative value to dissolution, and where

\(a_m\) = mineral specific surface area [m\(^{-1}\)]

\({\mathcal P}_{ml}\) = prefactor (a sum of prefactor rates; if activation energy is provided the Arrhenius equation is applyied to each prefactor to calculate rates at different temperatures)

\(K_m\) = equilibrium constant

\(Q_m\) = ion activity product

\(\sigma_m\) = Temkin number (default is 1)

\(\lambda_m\) = mineral scaling factor (default is 1)

\(\beta_m\) = affinity power (default is 1)

\(k_{ml}\) = rate constant

Required Cards:

MINERAL_KINETICS

Opens the block.

<string>

Specifies mineral name.

RATE_CONSTANT <float> <optional units_string>

Kinetic rate constant. If negative, then raised to power 10 (e.g. -12.d0 is converted to \(10^{-12}\)) (default units [mol/m²-sec])

Optional Cards:

ACTIVATION_ENERGY <float>

If specified, used in the prefactor calculations for temperature dependent rates. (Arrhenius) [J/mol]

AFFINITY_THRESHOLD <float>

If specified, rate is only calculated if \(K_m Q_m \geq\) threshold and \({\rm sign}(1-K_mQ_m) < 0\) corresponding to precipitation.

AFFINITY_POWER

\(\beta_m\) in Eqn. (1) above.

MINERAL_SCALE_FACTOR

\(\lambda_m\) in equation above.

PREFACTOR

Parameters for reaction rate prefactors

RATE_LIMITER <float>

Limiting reaction rate factor (see Eqn. (27) in Theory Guide, Mode: Reactive Transport for details).

SURFACE_AREA_POROSITY_POWER <float>

Exponent in equation for transient mineral surface area calculated as a function of porosity, \(\porosity\): \(a_m = a_m^0 (\porosity/\porosity_0)^n\), \(n\) = SURFACE_AREA_POROSITY_POWER.

SURFACE_AREA_VOL_FRAC_POWER <float>

Exponent in equation for transient mineral surface area calculated as a function of the mineral volume fraction \(\porosity_m\): \(a_m = a_m^0 (\porosity_m/\porosity_m^0)^n\), \(n\) = SURFACE_AREA_VOL_FRAC_POWER. Note that the volume fraction power can be applied only if \(\porosity_m^0 > 0\) corresponding to primary minerals.

TEMKIN_CONSTANT

Sigma in Eqn. (1) above.

Examples

CHEMISTRY
  ...
  MINERAL_KINETICS
    Calcite
      RATE_CONSTANT 1.d-13 mol/cm^2-sec
    /
  /
  ...
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