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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

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

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

\(a_m\) = mineral surface area

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

\(K_m\) = equilibrium constant

\(Q_m\) = ion activity product

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

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

\(k_{ml}\) = rate constant

Note that prefactor calculations have not yet been verified.

Required Cards:

MINERAL_KINETICS
Opens the block.

Optional Cards:

<string>
Specifies mineral name.
RATE_CONSTANT <float>
Kinetic rate constant [mol/m2-sec]. If negative, then raised to power 10 (e.g. -12.d0 is converted to \(10^{-12}\))
ACTIVATION_ENERGY <float>
If specified, used in the prefactor calculations for temperature specific rates (Arrhenius)
AFFINITY_THRESHOLD <float>
If specified, rate is only calculated if Q/K >= threshold and sign < 0 corresponding to dissolution.
RATE_LIMITER <float>
If specified, \(R=-\frac{\Omega}{1+\frac{1-\Omega}{R_{lim}}}\), where \(R_{lim}\) is the rate limiter, \(\Omega=Q/K\), and \(R\) denotes the reaction rate.
IRREVERSIBLE
Flag indicating the reaction is irreversible
SURFACE_AREA_POROSITY_POWER <float>
Exponent in equation for transient mineral surface area calculated as a function of porosity, \(\phi\). \(A = A_0 (\phi/\phi_0)\)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 \(\phi_m\). \(A_m = A_m^0 (\phi_m/\phi_m^0)\)SURFACE_AREA_VOL_FRAC_POWER. Note that the volume fraction power can be applied only if \(\phi_m^0 > 0\) corresponding to primary minerals.
PREFACTOR
Parameters for reaction rate prefactors

Examples

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