Convergence Error in Transport Problem

[banjo]

Hello,

I am modelling my column study and have come across a problem that I can't seem to fix. After 4 pore volumes I get an error message the S has not converged. I know my code works with a different set of solutions but I'm super new to PHREEQC and don't know what to do to fix this set. I used the chemistry of the solutions used in my experiments. Any and all advise would be appreciated. Thank you for reading.

Here is my code:

Code: [Select]

SOLUTION 0 Simulated Surface Water
    temp      25
    pH        7.81
    pe        4
    redox     pe
    units     mg/l
    density   1
    Alkalinity 41 gfw 50.04
    Ca        6.98
    Cl        7.24
    K         14.33
    Mg        3.72
    Na        7.88
    S(6)      18.85
    -water    0.7 # kg
SOLUTION 1-50 Column pore water after simulated runoff flushing stage
    temp      25
    pH        9.665
    pe        4
    redox     pe
    units     mg/l
    density   1
    Alkalinity 588.79 gfw 50.04
    Ca        34.77
    Cl        612.17
    K         565.76
    Mg        95.33
    N(-3)     40.1
    N(5)      45.64
    Na        309.48
    P         0.1234 as PO4
    S(6)      226.18
    -water    0.07 # kg
END
EXCHANGE 1-50
    X       0.0275 #units in mol
    -equilibrate with solution 1
    -pitzer_exchange_gammas false
END

TRANSPORT
    -cells                 50
    -shifts                500 #10 PV
    -time_step             103680 # seconds.
    -boundary_conditions   constant flux
    -lengths               50*0.014 #70 cm column length.
    -dispersivities        50*0.002
    -correct_disp          true
    -diffusion_coefficient 0
    -print_cells           50
    -print_frequency       25
    -punch_cells           50

[dlparkhurst]

I had no problem using phreeqc.dat, but convergence failed will llnl.dat.

I think the problem has to do with trying to find redox equilibrium. llnl.dat has some unlikely redox states in my view, whereas phreeqc.dat has a relatively simple set. Regardless, I think if you add this code at the start of your input file, the redox state will be better poised, and the simulation will run. This species has a minimal effect on the distribution of species, but gives the redox equation a sufficient concentration to converge.

Code: [Select]

SOLUTION_SPECIES
H2O + 0.01e- = H2O-0.01
log_k -9
END

If this does not fix your problem, tell me which database you are using.

[banjo]

That solved it! Thank you so much. I was using phreeqc.dat