Processes > Reactive transport modelling

How does the mineral precipitation considered during transport?

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Yongqiang:
Hi David,

When the PHREEQCRM is coupled for reactive transport modelling, the GetConcentration and SetConcentration functions are applied. I wonder how the precipitated mineral is considered in this case. I am confused that the Getconcentration and Setconcentration methods can still retrieve the element in the precipitated minerals.

Thanks,

dlparkhurst:
GetConcentrations retrieves only the concentrations in the aqueous phase, and SetConcentrations applies only to the aqueous phase. GetConcentrations does not retrieve element moles or concentrations from other reactants: equilibrium phases, exchange, gas phase, solid solutions, surfaces, or kinetics.

If you use SetConcentrations, then RunCells, and say calcite precipitates, then the concentrations of Ca, C, and O will be less when you use GetConcentrations after RunCells.

If you use BMIPhreeqcRM, then you can use GetValue("equilibrium_phases_moles_Calcite") to retrieve the moles (not concentration) of calcite in each cell, and GetValue("equilibrium_phases_delta_moles_Calcite") to retrieve the change in moles of calcite in each cell that occurred in the RunCells calculation. Other strings can be used to retrieve data related to exchange, surface, etc. A list of the data items that can be retrieved by GetValue for a model system can be obtained by the BMI method GetOutputVarNames.

Alternatively, you can write to selected output using SELECTED_OUTPUT and USER_PUNCH definitions. You will need to use the PhreeqcRM methods related to selected output to select and retrieve the selected output information (SetCurrentSelectedOutputUserNumber, GetSelectedOutput, and related methods).

Yongqiang:
Many thanks, David.
May I ask if the method RM_GetSpeciesConcentrations can do a similar job to retrieve the amount of mineral precipitation?

dlparkhurst:
RM_GetSpeciesConcentrations returns the concentrations of all aqueous species for all cells. It does not return amounts of mineral precipitation.

If you run RM_GetSpeciesConcentrations and sum all of the Ca species, like Ca+2, CaHCO3+, and others, you will get the same value that is returned for calcium for RM_GetConcentrations.

Yongqiang:
Many thanks, David.
This is indeed a new knowledge to me.

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