How to utilize the different exchange capacity in one model?

[Jeonghwan Hwang]

Hi, this is Jeonghwan Hwang.
I've got a lot of help in this forum, thank you for kindly help.

Now I made a similar cation exchange model that i wanted.
I change the selectivity coefficient and exchange capacity values with my own results.

However, there are some problems in my model when it run.
I have to change the exchange capacity as different Cs concentration, based on my real experiments.
Although i inputted the different values with EXCHANGE 1 to EXCHANGE 5,
The simulation results only use EXCHANGE 1 in my model.

This is my code as follows:
=====================================================
database c://phreeqc/database/wateq4f.dat # database set
Title Initial solution
Solution 1
   pH 7
   Units g/l
save solution 1
end

TITLE Caesium Sorption experiment

use solution 1

EXCHANGE_MASTER_SPECIES
   X   X- #planar
   D   D- #TypeII
   Z   Z- #FES
   
EXCHANGE_SPECIES #Fuller는 Na 기준으로 제작
   D- = D- #TypeII # 동일
   log_k 0.0
   Na+ + D- = NaD #TypeII #Cs 기준으로 변경
   log_k -3.57
   K+ + D- = KD #TypeII #Cs 기준으로 변경
   log_k -1.43
   H+ + D- = HD #TypeII #Cs 기준으로 변경
   log_k 1.73
   Ca+2 + 2D- = CaD2 #TypeII #Cs 기준으로 변경
   log_k -6.06
   
   Z- = Z- #FES # 동일
   log_k 0.0
   Na+ + Z- = NaZ #FES #Cs 기준으로 변경
   log_k -6.68
   K+ + Z- = KZ #FES #Cs 기준으로 변경
   log_k -4.53
   H+ + Z- = HZ #FES #Cs 기준으로 변경
   log_k -4.88
   Ca+2 + 2Z- = CaZ2 #FES #Cs 기준으로 변경
   log_k -15.17
   
   X- = X- #planar # 동일
   log_k 0.0   
   H+ + X- = HX #planar #Cs 기준으로 변경
   log_k 0.74   
   K+ + X- = KX #planar #Cs 기준으로 변경
   log_k -0.77   
   Na+ + X- = NaX #planar #Cs 기준으로 변경
   log_k -1.76
   Ca+2 + 2X- = CaX2 #planar #Cs 기준으로 변경
   log_k -4.63   
      
EXCHANGE 1 # SL ratio 0.5
   X 5.90E-05
 #planar
   D 1.47E-05
 #TypeII
   Z 1.84E-07
 #FES
-equilibrate solution 1
save exchange 1

EXCHANGE 2 # SL ratio 1
   X 1.18E-04
 #planar
   D 2.94E-05
 #TypeII
   Z 3.68E-07
 #FES
-equilibrate solution 1
save exchange 2

EXCHANGE 3 # SL ratio 2.5
   X 2.95E-04
 #planar
   D 7.35E-05
 #TypeII
   Z 9.20E-07
 #FES
-equilibrate solution 1
save exchange 3

EXCHANGE 4 # SL ratio 15
   X 1.77E-03
 #planar
   D 4.41E-04
 #TypeII
   Z 5.52E-06
 #FES
-equilibrate solution 1
save exchange 4

EXCHANGE 5 # SL ratio 100
   X 1.18E-02
 #planar
   D 2.94E-03
 #TypeII
   Z 3.68E-05
 #FES
-equilibrate solution 1
save exchange 5

end

TITLE Sorption of caesium

EXCHANGE_SPECIES
   Cs+ + X- = CsX #planar #Cs 기준으로 변경
   log_k 0
   Cs+ + D- = CsD #TypeII #Cs 기준으로 변경
   log_k 0
   Cs+ + Z- = CsZ #FES #Cs 기준으로 변경
   log_k 0

PHASES
   Fix_H+
   H+ = H+
   log_k 0.0
SELECTED_OUTPUT
    -file [Hwang1]
    -m Cs+ CsX CsD CsZ
    -t Cs
   
   use exchange 1
   use solution 1
   solution 2
      ph 7
      units moles/l
      Cs 9.64E-08
      
   use exchange 2
   use solution 1
   solution 3
      ph 7
      units moles/l
      Cs 1.00E-06
      
   use exchange 2
   use solution 1
   solution 4
      ph 7
      units moles/l
      Cs 1.00E-05
      
   use exchange 3
   use solution 1
   solution 5
      ph 7
      units moles/l
      Cs 1.15E-04
   
   use exchange 4
   use solution 1
      solution 6
      pH 7
      units moles/l
      Cs 1.04E-03
      
   use exchange 5
   use solution 1
   solution 7
      ph 7
      units moles/l
      Cs 9.57E-03
end

USE EXCHANGE 1
use solution 2
EQUILIBRIUM_PHASES 1; Fix_H+ -7.0 RbOH 10.0
end

USE EXCHANGE 2
use solution 3
EQUILIBRIUM_PHASES 1; Fix_H+ -7.0 RbOH 10.0
end

USE EXCHANGE 2
use solution 4
EQUILIBRIUM_PHASES 1; Fix_H+ -7.0 RbOH 10.0
end

USE EXCHANGE 3
use solution 5
EQUILIBRIUM_PHASES 1; Fix_H+ -7.0 RbOH 10.0
end

USE EXCHANGE 4
use solution 6
EQUILIBRIUM_PHASES 1; Fix_H+ -7.0 RbOH 10.0
end

USE EXCHANGE 5
use solution 7
EQUILIBRIUM_PHASES 1; Fix_H+ -7.0 RbOH 10.0
end
=====================================================

In my model, I make 5 different solid-solution ratio, and i assume that they effected to exchange capacity.
And i use RbOH to converge the model, because Rb doesn't effect the exchange process in my model.

Any comments can help me.
Thank you for reading.

Respectfully,

Jeonghwan Hwang

[dlparkhurst]

You need to separate the calculations with END keywords. Although you define SOLUTION 2, the USE statement will take precedence in the reaction calculation, so EXCHANGE 1 will react with solution 1. If you want to react with SOLUTION 2, you should remove the USE keyword.

   use exchange 1
  # use solution 1
   solution 2
      ph 7
      units moles/l
      Cs 9.64E-08
  END
   
   use exchange 2
 #remove  use solution 1
   solution 3
      ph 7
      units moles/l
      Cs 1.00E-06
 END

Also, SAVE is not necessary for initial exchange calculations. So, here is the way I think it should be:

EXCHANGE 1 # SL ratio 0.5
   X 5.90E-05
 #planar
   D 1.47E-05
 #TypeII
   Z 1.84E-07
 #FES
-equilibrate solution 1
#remove save exchange 1
END