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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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