> 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
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