Your rate expression is pretty complicated, so I have not completely analyzed your input file. I'll just make a couple comments. (1) The formulas for the kinetic reactions must be charge balanced. From what I see, you have H -2 Cu +1 OH -1. This does not look right to me. Should it be CuOH 2? or just Cu+1 H -2? There does not appear to be a need for the second kinetic reaction because it is the same rate as the first, couldn't you do the same thing with an additional OH -1 in the first rate? (2) I think another problem may be the fraction of a kilogram of water in your solutions. TOT returns molality. However, the SAVEd value is moles. You probably need to multiply all TOT functions by TOT("water") or the final moles by TOT("water") to keep the units consistent. TOT("water") is the mass of water in kilograms. I'd try a first order rate expression first to make sure everything is working as you expect before you go to the full expression that you have. David 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 xiaomin Mao <xmao@xxxxxxxx> To: dlpark@xxxxxxxx cc: 05/25/03 06:21 AM Subject: PHREEQC problem Dear Parkhurst, I am a research staff from Edinburgh Univ. in U.K. PHREEQC is a programme I like, and recently we even coupled Modflow, Mt3dms with PHREEQC for reactive transport modelling with dencity dependent flow. Now, I have a trouble with PHREEQC modelling and need you help. I am using PHREEQC for a transport modelling with kinetic sorption of Cu by organic matter. The kinetic sorption was written based on Nica-Donna model, and the parameter used is from Christopher J. Milne (2003). I am wondering why the simulation is so slow(or stopped) if the organic matter get a little larger. Is it because the numerical convergence problem? or, could you give me any suggestion on how to avoid such problem? thank you very much. Xiaomin ---------------- Dr. Xiaomin MAO Institute for Infrastructure and Environment School of Engineering and Electronics The University of Edinburgh Edinburgh, EH9 3JN U.K. Tel: +44 131 650 5810 Fax: +44 131 667 9238 http://myprofile.cos.com/maoxm The input file is as follows, Rates Org_xcu -start 10 Cu_conc=Tot("Cu") 20 H_conc=ACT("H+") 30 Org_xcue1=4.722* (1.8197*Cu_conc)^0.53/((1.8197*Cu_conc)^0.53+(218.78*H_conc)^0.66) *((1.8197*Cu_conc)^0.53+(218.78*H_conc)^0.66)^0.59/(1+((1.8197*Cu_conc)^0.53+(218.78*H_conc)^0.66)^0.59) 33 Org_xcue2=0.8811* (181970086*Cu_conc)^0.36/((181970086*Cu_conc)^0.36+(398107171*H_conc)^0.76) *((181970086*Cu_conc)^0.36+(398107171*H_conc)^0.76)^0.7/(1+((181970086*Cu_conc)^0.36+(398107171*H_conc)^0.76)^0.7) #0.0001*Cu_conc/(Cu_conc+H_conc)*parm(1) 35 rate1=-(0.0001*(Org_xcue1+Org_xcue2)-Kin("Org_xcu"))/10 # 0.0001--based on the quantity of organic matter 37 put(rate1,1) 40 moles=rate1 *time 45 if Tot("Cu")+moles < 0 then moles = -TOT("Cu")/3 50 save moles -end Org_xh -start 35 rate1=get(1) 40 moles=-rate1*time 50 save moles -end end SOLUTION 0 CCA concentration units mol/kgw pH 7.0 charge pe 4 -water 0.03375 Na 1 Cl 1 SOLUTION 1 CCA concentration units mol/kgw pH 4.0 pe 4 -water 0.03375 Cu 0.123562 Na 1 Cl 1.3 charge SOLUTION 2-16 CCA concentration units mol/kgw pH 4.0 charge pe 4 -water 0.03375 Cu 0.00 Na 1 Cl 1 kinetics 1-16 Org_xcu -Formula H -2.0 Cu +1 -m0 0.00 -m 0.00 #-Parms 0.1 Org_xh -Formula H 0 -m0 0.1 -Parms 0.1 TRANSPORT -cells 16 -shifts 33 -time_step 30857 #10.5d/28*86400s/d -flow_direction forward -lengths 16*5e-3 -boundary_conditions flux flux -dispersivities 16*0.012 -correct_disp true -diffusion_coefficient 0.0000 -punch_cells 16 -punch_frequency 1 -warnings false SELECTED_OUTPUT -file C:\cca_tmp\cca1 -selected_out true -user_punch true -reset false USER_Graph -start 10 PUNCH ToT("Cu"), -LM("H+"),Kin("Org_xcu"),Kin("Org_xh") -end END
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