Re: Questions concerning Phreeqc

["David L Parkhurst" <dlpark@xxxxxxxx>]

> My problem now is that
> 1)   Sr is not transported into the cells. I tried to refine the grid, to
increase the time step and to increase the diffusion coefficient, but
either
the calculation takes too long and finds no end or the results show no Sr
in
the cells.

I think the boundary conditions should be "constant closed". I think that
no strontium is transported into the column because there is no advection.
I'm cc'ing this to Tony Appelo, who can explain the diffusion option better
than I. If you want the Sr to diffuse farther into the system, you probably
need to make a longer column.

> 2)   the porewater should be in equilibrium with the defined reactions
and
as long as no Sr is entering the cells the porewater composition should
stay
constant. But I fear that the reactions are repeated with every time step
(e.g. the Na and Cl are changing continously). How can I define, that the
reactions are in equilibrium with the porewater as long as no influence
from
outside takes place?

I have rearranged your input file to redefine the initial conditions using
a batch reaction with number "100" for all of the pieces and then saving
the results to numbers (cells) 1-10. In this way, REACTION is not defined
for cells 1-10, so there is no continuous source of chloride through the
calculation. (You'll have to use a bigger number if you expand your column
to 100 cells or greater.

David

TITLE "calculation of bentonite porewater and diffusion of Sr into column"

# diffusive transport.pqi
# minteq.dat

EXCHANGE_MASTER_SPECIES
      X     X-
      Xa     Xa-

EXCHANGE_SPECIES
      X- = X-
      log_k       0.0

      Xa- = Xa-
      log_k       0.0

      Na+ + X- = NaX
      log_k       20.0

      Na+ + Xa- = NaXa
      log_k       20.0

# Selectivity constants after Wanner et al. (1994)
      H+ + NaX = HX + Na+
      log_k       4.57

      K+ + NaX = KX + Na+
      log_k       0.26

      Ca+2 + 2NaX = CaX2 + 2Na+
      log_k       0.21

      Mg+2 + 2NaX = MgX2 + 2Na+
      log_k       0.13

      H+ + NaXa = HXa + Na+
      log_k       3.0

      K+ + NaXa = KXa + Na+
      log_k       0.26

      Ca+2 + 2NaXa = CaXa2 + 2Na+
      log_k       0.21

      Mg+2 + 2NaXa = MgXa2 + 2Na+
      log_k       0.13

SURFACE_MASTER_SPECIES
      Surf_s      Surf_sOH

SURFACE_SPECIES
      Surf_sOH = Surf_sOH
      log_k       0.0

      Surf_sOH + H+ = Surf_sOH2+
      log_k       5.4

      Surf_sOH = Surf_sO- + H+
      log_k       -6.7

SOLUTION 100 groundwater
temp      13
pH        7.3
pe        -4.4
redox     pe
units     mg/kgw
density   1.0
Na          1887
K           9.1
Mg          86.4
Ca          770
Cl          4210
S(6)        308
Alkalinity  155

EXCHANGE 100
      NaX   53.4318e-3
      CaX2  4.6107e-3
      MgX2  1.2753e-3
      KX    0.1962e-3
      NaXa  2356.73454e-3
      CaXa2 203.36571e-3
      MgXa2 56.25009e-3
      KXa   8.65386e-3

SURFACE 100
      Surf_s      80.76936e-3 3.    2884.62

EQUILIBRIUM_PHASES 100
      Gypsum      0.0   0.076
      Calcite     0.0   0.53799
      Quartz      0.0   6.4013

REACTION 100
      NaCl
      0.004607 moles
SAVE solution 1-10
SAVE exchange 1-10
SAVE Surface 1-10
SAVE equilibrium_phases 1-10
END

SOLUTION 0
temp  13
pH    7
Sr    1e-3
Cl    1e-3

TRANSPORT
      -cells      10
      -shifts     10
      -time_step  3.15e7
      -flow_direction   diffusion_only
      -boundary_conditions    constant closed
      -lengths    0.035
      -diffusion_coefficient  5.0e-10

SELECTED_OUTPUT
      -file diffusive_transport.sel

USER_PUNCH
      -head Na+ Cl- Sr+
      10 PUNCH TOT ("Na")*1000, TOT("Cl")*1000, TOT("Sr")*1000

END


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


                                                                                                                          
                      "Klennert,                                                                                          
                      Nicole"                  To:      "'dlpark@xxxxxxxx'" <dlpark@xxxxxxxx>                             
                      <Nicole.Klennert         cc:                                                                        
In-Reply-To: <AD47E2B18130D311BA6600E02944BCBA15A5EC@xxxxxxxxxxxxxxxxxxx>
                      @bgr.de>                 Subject: Questions concerning Phreeqc                                      
                                                                                                                          
                      11/21/01 08:45                                                                                      
                      AM                                                                                                  
                                                                                                                          
                                                                                                                          




Hello!

I am using the Phreeqc interactive alpha version 2.4.2 and I have some
problems with the transport calculations. I know there must be something
wrong with the way I defined the input file. I hope I do not waste your
time
and you can give me some assistance in this problem ?!

I am trying to model a 1D pure diffusive transport through a bentonite
column (no advection, no dispersion). My intention is first to calculate
the
bentonite porewater including cation exchange, surface complexation,
equilibrium phases, and reaction. Next, the resulting porewater and changed
exchanger, surface, and phases in equilibrium with the porewater represent
the volume of the column cells and Sr is injected at one column end as
solution 0. In this way  I expect to see how Sr diffuses through the
column,
how it is retarded by the exchanger surface and how the exchanger, the
surface, the amount of phases and the porewater composition change with
time.

My problem now is that
1)   Sr is not transported into the cells. I tried to refine the grid, to
increase the time step and to increase the diffusion coefficent, but either
the calculation takes too long and finds no end or the results show no Sr
in
the cells.
2)   the porewater should be in equilibrium with the defined reactions and
as long as no Sr is entering the cells the porewater composition should
stay
constant. But I fear that the reactions are repeated with every time step
(e.g. the Na and Cl are changing continously). How can I define, that the
reactions are in equilibrium with the porewater as long as no influence
from
outside takes place?

I attached the input file to this mail and I hope you have an idea about
what I did wrong.

Thank you very much in advance and best regards,

Nicole Klennert

(See attached file: diffusive transport.pqi)


---------------------------------------------------------------------------
Dipl.-Geol. Nicole Klennert
Federal Institute for Geosciences and Natural Resources
Stilleweg 2
30655 Hannover
Germany

+49-(0)511-643-0                     (switchboard)
+49-(0)511-643-3719            (direct)
+49-(0)511-643-3694            (fax)

nicole.klennert@xxxxxx
www.bgr.de

Attachment: diffusive transport.pqi
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