Re: PHREEQC problem

[xiaomin Mao <xmao@xxxxxxxx>]

Thank you, David.
About (1), I don't understand why you write: H -2 Cu +1 OH -1. I write in the kinetic expression:
 -Formula  H -2.0 Cu +1
will it be any problem?
To (2), I think I have noticed the difference. TOT is used to get the concentration of Cu in the solution which is
required according to the model. As the water in each cell is only 0.03375 kg, the organic matter is calculated based
on the quantity of soil and ratio of organic matter in each cell. therefore, it seems not to be the problem.
Is there any other reason?
cheers,
xiaomin

David L Parkhurst wrote:

> 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