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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