Apply different methods (no_edl, diffuse_layer, cd_music) in one calculation?

[Pak]

I have not found an example or previous post that discusses such question (Which it does not mean that it exists).

I am wondering how I can do the following in Phreeqc:

a) I have a surface species X1 that uses a diffusive layer approach (Gouy-Chapman), other surface X2 that uses a no_edl (non electrostatic diffusion layer) and other that uses a cd_music X3.

b) I would like them to interact during the same calculation with a solution.

How do I handle it in Phreeqc?

I have tried to do using the following Phreeqc script:

Solution 1
x
x
x
Surface 1
X1
-diffuse_layer
X2
-no_edl
X3
-cd_music

From my calculations such approach does not seem to work (All surface will compute with the diffuse layer appraoch). How can I do it?

Thank you

[dlparkhurst]

Here is a paragraph from the description of the SURFACE data block from the manual for version 3 (Note: the citation for version 3 is Parkhurst, D.L., and Appelo, C.A.J., 2013, Description of input and examples for PHREEQC version 3—A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Techniques and Methods, book 6, chap. A43, 497 p., available only at http://pubs.usgs.gov/tm/06/a43.)

"SURFACE 3 defines a CD-MUSIC surface. The data are based on a description of binding on goethite (Hiemstra and Van Riemsdijk, 1996; Rahnemaie and others, 2006) that has two site types (Goe_uni and Goe_tri). The identifiers -equilibrate , -diffuse_layer , -sites_units , -cd_music , -Donnan , -only_counter_ions , and -no_edl apply to all surfaces and site types in the surface assemblage. The identifier -capacitances is defined for each individual CD-MUSIC surface and does not apply to the entire surface assemblage. A combination of CD-MUSIC, diffuse double layer, and -no_edl surfaces cannot be used directly in a SURFACE assemblage. However, a diffuse-double-layer surface, like Surfa in SURFACE 1, will keep its properties in a CD-MUSIC surface assemblage when defined with very high capacitances; for example, -capacitances 1e5 1e5. Similarly, a -no_edl surface will keep its properties in a diffuse-double-layer surface if the surface area is very large (1 × 10 10 m 2 [square meter] for the product of specific_area_per_gram and grams ). By extension, a -no_edl surface will keep its properties when defined in a CD_MUSIC surface assemblage if the surface area and capacitances are large. Thus, with these special definitions, -cd_music can be used to model simultaneously all of the available types of surfaces ( -no_edl , diffuse double layer, and CD-MUSIC). If a -no_edl surface with a large surface area is included in an assemblage together with identifier -Donnan , the thickness may have to be set to a small number to avoid the situation where the volume of EDL water becomes unrealistically large."

[Annr]

And If I want to use just two type of surfaces (-no edl and ddl) what I need to do?
Can I use DDL model and write high surface area for no-edl surface site? Will it right or not?

Thank you!

[dlparkhurst]

"a -no_edl surface will keep its properties in a diffuse-double-layer surface if the surface area is very large (1 × 10 ^10 m 2 [square meter] for the product of specific_area_per_gram and grams )."

So, yes, a surface with a high surface area will be effectively no_edl when defined in a SURFACE that uses the default (no -no_edl and no -cd_music  option).

Note the description of SURFACE has errors. It should state that the default (diffuse_double layer), -no_edl, and -cd_music are mutually exclusive. The text says -diffuse_layer instead of default, which is incorrect; -diffuse layer refers to the explicit calculation of the diffuse layer composition and not the type of surface complexation model.

[Pak]

I try to obtain the same values using a classical surface approach (diffusive layer) and the CD-Music approach. The files are attached. They look like:

case A diffuse layer:
SOLUTION 1
....
Surface 1
-equilibrate 1
Hfo_s 0.00143 600 11.4    #  0,005 mol/mol Fe bzw. Al
Hfo_w 0.0572                #  0,2 mol/mol Fe bzw. Al

case B cd-music:
SOLUTION 1
....
Surface 1
-equilibrate 1
-cd_music
Hfo_s 0.00143 600 11.4    #  0,005 mol/mol Fe bzw. Al
Hfo_w 0.0572                #  0,2 mol/mol Fe bzw. Al
-capacitance   1.00E+05      1.00E+05

I have understood from the citation of Parkhurst (see above post) which is drawn from the manual, that in order to reproduce a ddl I only have to give high capacitances, but doing such thing (Case B) I obtain a -no_edl (I think) since:
 exp(-F*psi/RT) = 1

Does somebody know where I am doing the mistake?

Thank you

[dlparkhurst]

You must define SURFACE_SPECIES with -cd_music with the change in charge on the first plane.

Code: [Select]

SURFACE_MASTER_SPECIES
    Surf          SurfOH       

SURFACE_SPECIES
SurfOH = SurfOH
    log_k     0
SurfOH = SurfO- + H+
    log_k     -8.93
H+ + SurfOH = SurfOH2+
    log_k     7.29
Cl- + SurfOH = SurfOHCl-
    log_k     0
Na+ + SurfOH = SurfONa + H+
    log_k     0

END
SOLUTION 1
    temp      25
    pH        5
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Cl        1 charge
    Na        1
    -water    1 # kg
END
SURFACE 1
    -equilibrate with solution 1
    SurfOH     1         1         600
END
SURFACE_MASTER_SPECIES
    Surfcd        SurfcdOH     

SURFACE_SPECIES
SurfcdOH = SurfcdOH
    log_k     0
SurfcdOH = SurfcdO- + H+
    log_k     -8.93
    -cd_music -1 0 0 0 0
H+ + SurfcdOH = SurfcdOH2+
    log_k     7.29
    -cd_music 1 0 0 0 0
Na+ + SurfcdOH = SurfcdONa + H+
    log_k     0
Cl- + SurfcdOH = SurfcdOHCl-
    log_k     0
    -cd_music -1 0 0 0 0
END
SURFACE 1
    -equilibrate with solution 1
    SurfcdOH    1         1         600
        -capacitance 1e+05  1e+05
    -cd_music
END


[Pak]

Thanks