[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: question about PHAST/PHREEQC-- with attachments




Try the file below. Here are the major changes:

(1) You should define Benzene as a separate "element" if you want it to
react kinetically. If you define it as part of "C", it will react to
equilibrium, which in this case means that all of the C6H6 would probably
disappear instantly to come to equilibrium with the rest of the C system.

(2) Signs for kinetic reactions are tricky. The product of the "moles"
saved and the reaction coefficients in -formula determine whether an
element(s) enter or leave solution; negative indicates decreasing
concentration in solution, positive increasing. Here, the number of "moles"
is negative, Benzene 1 is positive and so benzene concentration decreases;
C6H6 -1 is negative so the product of "moles"*-1 is positive and C6H6
increases in solution.

The kicker is that positive "moles" decreases the number of moles of a
kinetic reactant (-M in KINETICS definition and Basic variable M in a rate
expression). The program stops the reaction when 0 moles of reactant are
left. By using a negative "moles", the amount of reactant increases, so the
reaction will continue indefinitely, which is what you want in this case I
think. The number of moles of the kinetic reactant (Basic variable M) will
be the total number of moles of benzene reacted in a given cell.

(3) You can't specify both a concentration of O2 and a pe with a specified
O2 concentration. In this case, the pe (in equilibrium with a specified
pO2) will determine the O2 concentration.

David


SOLUTION_MASTER_SPECIES
#C(6)     C6H6           0.0     C6H6            78.108
Benzene   Benzene       0     C6H6  78.108
SOLUTION_SPECIES
#C6H6 = C6H6
Benzene = Benzene
 log_k           0.000
        -gamma    5.4000    0.0000

#6 CO3-2 + 12 H+ = C6H6 + 3 H2O + 7.5 O2
# log_k           0.000
#        -gamma    5.4000    0.0000
SOLUTION 1
 units mol/kgw
 pH  7.0 charge
 temp 25
# C(6)    0.001
Benzene     .001
END
SOLUTION 2
 units mol/kgw
 pH  7.0 charge
 pe 12.0 O2(g) -0.67
 temp 25
# O(0)    0.0001

END
KINETICS 1
 C6H6_degradation
# -formula C (H) 6.0 12.0
 -formula Benzene 1 C6H6 -1
 -m 0
 -m0 0
RATES
C6H6_degradation
-start
10 Ks = 1.0d-4
20 Ka = 3.125d-6
30 qm = 1.407e-3/3600
#40 f1 = MOL("C(6)")/(Ks + MOL("C(6)"))
40 f1 = MOL("Benzene")/(Ks + MOL("Benzene"))
50 f2 = MOL("O2")/(Ka + MOL("O2"))
60 rate = -qm * f1 * f2
70 moles = rate * TIME
90 SAVE moles
        -end

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




Project Home Page
Complete Water Resources Division Software
USGS Home Page
Water Resources Division Home Page
NRP Home Page
Help Page
USGS Privacy Statement       

Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.

Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. 


The URL of this page is: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/mail/msg00668.html
Email:dlpark@usgs.gov
Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
Visitor number [an error occurred while processing this directive] since Jan 22, 1998.