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Re: Thank alot!




Here are a few comments. Hematite is very insoluble, generating
concentrations of iron ~1e-14. PHREEQC has some problems with these low
concentrations, but the KNOBS and SOLUTION_SPECIES below help the program
to converge.

You may consider goethite as a more representative phase. Also, perhaps you
should include hematite or goethite along with pyrite. There is no source
of iron for forming pyrite.

Schoepite and uraninite are not calculated to coexist. In the initial
equilibration of solution 0 with both minerals, one dissolves completely.

You do not need the -steps in the KINETICS definition; the transport
calculation defines the time steps and the number of "shifts".

I generally would not include -step_divide.

You have two statements labeled 50 in the rate expression. The second one
will be used.

If you use stagnant zones, you must define solutions for the additional
cells. In your case they would be numbered 12-21, with 12 connected to 1,
13 to 2, ... 21 to 10. There appears to be a fatal bug when they are not
defined, which we will have to look into.

A large dispersivity relative to cell size will cause multiple "mixruns".
It is not an error, but it does slow the calculations down. You may want to
decrease the dispersivity until you have worked out the basic reactions,
and then increase it.

David


KNOBS
      -pe   2
      -step       2
      -iterations 200
SOLUTION_SPECIES
      H2O + .01e- = H2O-0.01
      log_k -9
TITLE  Rollfront

SOLUTION 0-10 Rainwater
        units            mmol/kgw
        temp           25.0
        pH              7.0     charge
        pe               4.0
EQUILIBRIUM_PHASES 0
      CO2(g)             -3          10
      O2(g)                    -0.7        10
SAVE  Solution 0
END

USE solution 0
EQUILIBRIUM_PHASES 1-2
      Schoepite   0.0          0.1
      Calcite           0.0          0.1
      Hematite    0.0          0.1
SAVE solution 1-2
END

USE solution 0
EQUILIBRIUM_PHASES 3-4
      Schoepite   0.0          0.1
      Calcite           0.0          0.1
      Pyrite            0.0          0.1
      Uraninite(c)      0.0          0.1
SAVE solution 3-4
END

KINETICS 5-10
      Organic_C
            -formula  CH2O
            -tol         1e-8
            -m0          1           # mol/kgw
            -m           1
#           -steps 51840000 in 100 steps               # 600 Tage
#           -step_divide 1000000
RATES
       Organic_C
 -start
10 if (m <= 0) then goto 200
20  mO2 = mol("O2")
30  mNO3 = tot("N(5)")
40  mSO4 = tot("S(6)")
50   rate = 1.57e-9*mO2/(2.94e-4 + mO2) + 1.67e-11*mNO3/(1.55e-4 + mNO3)
50   rate = 1.57e-7*mO2/(2.94e-4 + mO2)
#            60   rate = rate + 1.e-13*mSO4/(1.e-4 + mSO4)
60   rate = rate + 1.e-10*mSO4/(1.e-4 + mSO4)
70  moles = rate * m * (m/m0) * time
80 if (moles > m) then moles = m
200 save moles
 -end
END

TRANSPORT
        -cells                10
        -shifts               100
        -time_step            86400
        -length               1
        -dispersivities       2.0
      -punch_cells            1 2 3 4 5 6 7 8 9 10
        -punch_frequency      1
#        -stagnant            1      1.056e-10  0.05          0.15

PRINT
        -reset          false
SELECTED_OUTPUT
        -file           Rollfront.csv
        -reset          false
        -time           true
        -totals         U S Fe Ca
      -pH         false
      -pe         true
END


David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled




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