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ICs, BCs, fixes
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@ -29,61 +29,105 @@ mpirun -np 4 ./poet --interp barite_interp_eval.R barite_results
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The benchmark depicts an isotherm porous system at *25 °C* where pure
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water is initially at equilibrium with *celestite* (strontium sulfate;
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brute formula: SrSO_4).
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A solution containing only dissolved Ba^{2+} and Cl^- diffuses into
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the system causing celestite dissolution. The increased concentration
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of dissolved sulfate SO_{4}^{2-} induces precipitation of *barite*
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(barium sulfate; brute formula: BaSO_{4}^{2-}). The overall reaction
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can be written:
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brute formula: SrSO_{4}). A solution containing only dissolved Ba^{2+}
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and Cl^- diffuses into the system causing celestite dissolution. The
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increased concentration of dissolved sulfate SO_{4}^{2-} induces
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precipitation of *barite* (barium sulfate; brute formula:
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BaSO_{4}^{2-}). The overall reaction can be written:
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Ba^{2+} + celestite \rightarrow barite + Sr^{2+}
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Both celestite dissolution and barite precipitation are calculated
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using a kinetics rate law based on transition state theory:
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rate = -S_{m} K (1-SR_{m})
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rate = -S_{m} k_{barite} (1-SR_{m})
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where the reaction rate has units mol/s, S_{m} (m^{2}) is the reactive
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surface area, K (mol/m^{2}/s) is the rate constant, and SR is the
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saturation ratio, i.e., the ratio of the ion activity product of the
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reacting species and the solubility constant.
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surface area, k (mol/m^{2}/s) is the kinetic coefficient, and SR is
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the saturation ratio, i.e., the ratio of the ion activity product of
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the reacting species and the solubility constant, calculated
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internally by PHREEQC from the speciated solution.
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For barite, the reaction rate is computed as sum of two mechanisms,
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r_{/acid/} and r_{/neutral/}:
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rate_{barite} = S_{barite} (r_{/acid/} + r_{/neutral/}) * (1 - SR_{barite})
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rate_{barite} = S_{barite} (k_{/acid/} + k_{/neutral/}) * (1 - SR_{barite})
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where:
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r_{/acid/} = 10^{-6.9} e^{-30800 / R} \cdot act(H^{+})^{0.22}
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k_{/acid/} = 10^{-6.9} e^{-30800 / R} \cdot act(H^{+})^{0.22}
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r_{/neutral/} = 10^{-7.9} e^{-30800 / R}
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k_{/neutral/} = 10^{-7.9} e^{-30800 / R}
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R (8.314462 J K^{-1} mol^{-1}) is the gas constant.
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For celestite the kinetic law considers only the acidic term and
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For celestite the kinetic law considers only the acidic mechanism and
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reads:
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rate_{celestite} = S_{celestite} 10^{-5.66} e^{-23800 / R} \cdot
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act(H^{+})^{0.109} \cdot (1 - SR_{celestite})
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The kinetic rate laws as implemented in the =db_barite.dat= file
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accepts one parameter which represents reactive surface area in m^{2}.
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For the benchmarks the surface areas are set to
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The kinetic rates as implemented in the =db_barite.dat= file accepts
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one parameter which represents reactive surface area in m^{2}. For the
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benchmarks the surface areas are set to
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- S_{barite}: 50 m^{2}
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- S_{celestite}: 10 m^{2}
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A starting seed for barite is given at 0.001 mol in each domain
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element.
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** Initial conditions
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* TODO Nucleation
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The parametrization
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Geochemical benchmark inspired by Tranter et al. (2021) without
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nucleation.
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* POET simulations
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Currently these benchmarks are pure diffusion simulations. There are 7
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transported species: H, O, Charge, Ba, Cl, S(6), Sr.
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** =barite.R=
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- Grid discretization: square domain of 1 \cdot 1 m^{2} discretized in
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20x20 cells
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- Boundary conditions: E, S and W sides of the domain are closed; the
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N boundary has a *fixed concentration* (Dirichlet) of 0.1 molal
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BaCl_{2}
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- Diffusion coefficients: isotropic homogeneous \alpha = 1E-06
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- Time steps & iterations: 20 iteration with \Delta t = 250 s
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- *DHT* parameters:
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| H | 10 |
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| O | 10 |
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| Charge | 3 |
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| Ba | 5 |
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| Cl | 5 |
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| S(6) | 5 |
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| Sr | 5 |
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** =barite_interp_eval.R=
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- Grid discretization: rectangular domain of 40 \cdot 20 m^{2}
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discretized in 400 \cdot 200 cells
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- Boundary conditions: all boundaries are closed. The center of the
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domain at indeces (200, 100) has fixed concentration of 0.1 molal of
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BaCl_{2}
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- Diffusion coefficients: isotropic homogeneous \alpha = 1E-06
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- Time steps & iterations: 200 iterations with \Delta t = 250 s
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- *PHT* parameters:
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| H | 10 |
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| O | 10 |
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| Charge | 3 |
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| Ba | 5 |
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| Cl | 5 |
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| S(6) | 5 |
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| Sr | 5 |
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* References
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- Tranter, Wetzel, De Lucia and Kühn (2021): Reactive transport model
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of kinetically controlled celestite to barite replacement, Adv.
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Geosci., 1, 1–9 ,https://doi.org/10.5194/adgeo-1-1-2021
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of kinetically controlled celestite to barite replacement, Advances
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in Geosciences, 1, 1–9, https://doi.org/10.5194/adgeo-1-1-2021
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