User_Graph for TRANSPORT-boundary

[Felix]

Hello together! Hello Mr. Parkhurst!

I have encountered a problem that I would like to solve. Maybe I have your help?
Namely the following for the transport of two solutions: The User_Graph at the bottom of the script shows tailing towards the end. I would like to correct this skillfully. If I increase the shifts (e.g. to about 40), the tailing disappears, but the lines are drawn across the graph. Then another solution was discussed by lengthening the time step in the last cell: But I want to add kinetics later and fear a wrong mass balance. Is there a simple trick?

Many kind regards! A great forum!
Felix

Skript:

SOLUTION 0
     units   mol/L
        pH      4.76
        Temp    8.5
     C       5.774e-04

REACTION 1

NaCl 1
0.017 moles

SAVE SOLUTION 0
END

SOLUTION 1-20   Background value      
   units   mol/L
      pH      7.32
      Temp    8.5
   C       4.905e-03
   Ca      2.174e-03

END

TRANSPORT
        -cells                20   # 20 cells
        -length               10   # 10 m per cell   
        -shifts               20      # exchange onces
     -flow_direction       forward
     -boundary_conditions    flux flux
        -time_step            150000 # 2500 minutes
        -dispersivity         0.5
        -correct_disp       true
        -punch                1-20   # all 20 cells
        -punch_frequency      20   # output only for final value


USER_GRAPH
-headings x Chloride
-chart_title Transport-Test
-axis_titles "Distance (m)"  "Chloride (mg/l)" "pH"
-axis_scale X_axis 0 200
-axis_scale y_axis auto auto 
-initial_solutions false
-plot_concentration_vs x
10 GRAPH_X DIST
20 GRAPH_Y TOT("Cl")*35.453*1000
30 GRAPH_SY -la("H+")

END

[dlparkhurst]

The tailing is a result of dispersion. If you run for 10 shifts and -punch_frequency 10, you will see results after about 0.5 pore volumes have transited the column. As flow continues, this pattern will migrate across the graph until at 20 shifts, it is the pattern of your graph. Additional flow will move the pattern beyond the boundary.

If you set dispersivity to zero and diffusion coefficient to zero, the tailing will be eliminated (if you look at the scale, the variation in the curves is negligible).

The attached file makes a change so that REACTION 1 is not defined. With REACTION 1, the reaction is applied in cell 1 at each transport step.

[Felix]

Good evening Mr. Parkhurst,

many thanks for the fast reply! I reworked my REACTION-No. and included your script in my work now!

Best regards
Felix

[Kobare]

Good evening Mr. Parkhurst,

I wonder if its possible to create activity diagram of minerals using PHREEQC. If there is any solution I will appreciate.

Best regards
Kobare

[dlparkhurst]

It is possible to use PHREEQC to make activity diagrams. Example 6 shows a reaction path with phase boundaries.

A better way is to use PHREEPLOT by David Kinniburgh. It is based on PHREEQC and is designed to make phase and activity diagrams (along with fitting and other features). https://phreeplot.org/