Calcite precipitation simulation

[Charlie]

Im trying to assess calcite precipitation in a column. The simulation below suggests that calcite is at SI=0.0 but it doesn't seem to precipitate any moles of calcite. Am I missing something with this? Thanks


TITLE MODEL A1/C2


SELECTED_OUTPUT
-file model_A2.xls
-saturation_indices      CO2(g)  sepiolite calcite ##dolomite dolomite-dis dolomite-ord
-equilibrium_phases            sepiolite calcite ##dolomite dolomite-dis dolomite-ord
-pH                true
-Alkalinity          true
-solution             true
-reset            true
-simulation            true
-state            false
-distance            true
-charge_balance         true
-percent_error         true
-time               true
-step               true
-reaction            false



TRANSPORT                  
-cells   10                       ### cells per column      
-lengths    10*0.2            ### column total length      
-shifts   100               ### TOTAL shifts in simulation. NB: Total time = (total)shifts * timestep      
-time_step    10   yr         ### time per shift      
-porosities   5*0.25 5*0.25         ### 25% porosity in each cell   ## you can have different porosity for each cell   
-flow_direction forward                  
-boundary_conditions         flux # constant
-dispersivities   10*0.1
-correct_disp         true
-diffusion_coefficient         1.0e-9   ### m2/s
-warnings         false
-punch 10  ## 10th cell results at all time steps



SOLUTION 0  Displacing fluid
-units ppm
Na 100
Cl 200
Mg 300
Ca 1500
Alkalinity 800 as HCO3

SOLUTION 1-10 Initial pore water
-units ppm
Ca 10
K 100
Pb 50
Cl 100 Charge

EQUILIBRIUM_PHASES 1-10   ## Make up of country rock unit
sepiolite 0.0 0.01
calcite 0.0 0.0
##dolomite 1000.0 0.0
CO2(g)      -3.5    100


USER_GRAPH 1
    -chart_title      "10 cells * 0.2 m transport model - 10th CELL RESULTS - PORE VOLUMES"
    -headings               X Mg Na Cl
    -axis_titles            "Pore Volumes" "Total Moles/Kgw"
    -initial_solutions      false
    -connect_simulations    true
###-plot_concentrations_vs time
-start
10 graph_x (step_no + 0.5)/cell_no ## tranfer cell centered conc to column end
20 graph_y tot("Mg"), tot("Na"), tot("Cl")
-end

USER_GRAPH 2
    -chart_title      "10 cells * 0.2 m transport model - 10th CELL RESULTS - BREAKTHROUGH"
    -headings               TIME Mg Na Cl Ca pH
    -axis_titles            "TIME YEARS" "Total Moles/Kgw" "pH"
    -initial_solutions      false
    -connect_simulations    true
  ##  -plot_concentration_vs  x
  -start
10 GRAPH_X TOTAL_TIME/(60*60*24*365)       ## CONVERTS TO YEARS
20 graph_y tot("Mg"), tot("Na"), tot("Cl"), tot("Ca")
30 graph_sy -LA("H+")
-end

USER_GRAPH 3
    -chart_title      "10 cells * 0.2 transport model - 10th CELL RESULTS - BREAKTHROUGH"
    -headings               TIME equi_sepiolite equi_calcite #equi_dolomite
    -axis_titles            "TIME YEARS" "equi_mineral"
    -initial_solutions      false
    -connect_simulations    true
  ##  -plot_concentration_vs  x
  -start
10 GRAPH_X TOTAL_TIME/(60*60*24*365)       ## CONVERTS TO YEARS
20 graph_y EQUI("sepiolite"), EQUI("calcite")
#40 graph_sy EQUI("dolomite")
-end

USER_GRAPH 4
    -chart_title      "10 cells * 0.2 transport model - 10th CELL RESULTS - BREAKTHROUGH"
    -headings               TIME SI_sepiolite SI_calcite
    -axis_titles            "TIME YEARS" "SI" "SI"
    -initial_solutions      false
    -connect_simulations    true
  ##  -plot_concentration_vs  x
  -start
10 GRAPH_X TOTAL_TIME/(60*60*24*365)       ## CONVERTS TO YEARS
20 graph_y SI("sepiolite")
30 graph_sy SI("calcite")
-end

USER_GRAPH 5
    -chart_title      "10 cells * 0.2 transport model - 10th CELL RESULTS - BREAKTHROUGH"
    -headings               TIME kin_calcite
    -axis_titles            "TIME YEARS" "EQUI_DELTA"
    -initial_solutions      false
    -connect_simulations    true
  ##  -plot_concentration_vs  x
  -start
10 GRAPH_X TOTAL_TIME/(60*60*24*365)       ## CONVERTS TO YEARS
20 graph_y EQUI_DELTA("Calcite")

-end

END

[dlparkhurst]

All of the reaction happens in the first couple of cells. If you just look at cell 10, there is no dissolution or precipitation in that cell.

[Charlie]

Thanks for that David.  I also wanted to ask if it is possible to change composition of solution 0 part way through a simulation.  Essentially I want to flush through with a high pH solution then after half the time flush through with a low pH solution.  If not is there a simple way to save the column cell composition and then run again with the new solution 0?
Thanks

[dlparkhurst]

You can run TRANSPORT for the appropriate time using the initial flushing solution. Then you can redefine SOLUTION 0 and run another TRANSPORT simulation.

For the second TRANSPORT definition, you need only define parameters that you want to change. Usually, you will not change the solutions and reactants of the column, so you need no new SOLUTION, EQUILIBRIUM_PHASES,  etc for the column; they will be in the state at the end of the first TRANSPORT simulation. Also, the lengths, porosity, number of cells, and velocity (time step) will stay the same, so you need only define the number of shifts for the second TRANSPORT definition.