Zn and As Sorption onto smart polymers

[Juan Carlos Burillo]

Hi Brian:

 

We would like to model Zn and As sorption on smart polymers. React can model sorption onto mineral surface but we would like to know if we can use it for modeling onto a smart polymer. We are working with chitosan crosslinked with formaldehyde sinthesis and we are going to set Equilibrium Isoterm Tests with it. Zn-As Aqueous phases come from Acid Mine Drainage(AMD) produced in lab. We want to graph % analyte adsorbed vs pH, we would like to model adsorption using Langmuir, Kd or Freundlich isotherms. A graph of model with GWB and measure data (lab) sorption would be very interesting for us.

 

I expect you can help us

 

Best regards

 

Juan

[Brian Farrell]

Hi Juan,

 

It's hard to say for sure, but I think you can probably set up a simple model in React describing sorption onto your polymer. Unlike with the two-layer surface complexation model, one doesn't explicitly reference a specific mineral with the Kd, Freundlich, or Langmuir isotherms. Because the Kd and Freundlich isotherms refer to a fixed composition, the only parameter is the the value of the Kd, or the Kf and n for the Freundlich isotherm. With the Langmuir isotherm, you set Langmuir constants within the surface dataset. Then you set either the number of sorbing sites or the site density, but not the identity of the sorbing mineral or polymer, within your React script. So to summarize what I've said, React doesn't care about the nature of a sorbing surface when you're using the Kd, Freundlich, or Langmuir isotherm. As long as the Kd, Kf and n, or KL and site density you supply describe your data, you should be okay.

 

Modeling pH-dependent sorption behavior is another story, though. The Kd and Freundlich approaches can't do it because they're only valid for a system of fixed composition. You might be able to set up a Langmuir dataset with protonation and deprotonation of the surface site, but at that point it would be getting pretty complicated and it would probably be better to just develop a surface complexation model. The two layer surface complexation model in the GWB is like a multi-site Langmuir model that can account for protonation or deprotonation of the sorbing site (gives you pH-dependent sorption) and optionally can account for electrostatic effects. To ignore electrostatics, just set the electrical potential within the surface dataset to 0.

 

For more information on sorption and surface complexation, please see chapters 9 and 10 in Craig Bethke's Geochemical and Biogeochemical Reaction Modeling text.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC

[Juan Carlos Burillo]

Hi Brian:

 

Thank you for your fast response. I will try to set up a single model as you said. Looking for information in literature about polymer I may use Freundlich isotherm. Reading the GWB Essentials guide I have found that to invoke Freunlich isotherms, I must prepare a dataset of surface reacttions, using file "Freunlich.sdat" as a template. Please explain me how to prepare this dataset. Within TEdit- Freundlich.sdat ian see >Ni++, >Pb++ and >Sr+++ as default parameteres, I would like to include As and Zn too.

 

Best regards

 

Juan

[Brian Farrell]

Hi Juan,

 

You need to right-click "Surface species" or any of the listed species (>Ni++, >Pb++ and >Sr+++ in your case) and select "add" to add a new surface reaction to the dataset. Click in the box next to "Species" and choose your As or Zn species. The program will fill in the charge and mole weight of the species from the information in the thermo dataset, but you'll need to supply the Kf and nf. For more information, see sections 9.2.3 (Add and delete entries) and 9.2.5.3 (Kd and Freundlich datasets) in the GWB Essentials Guide.

 

Regards,

Brian

[Juan Carlos Burillo]

Hi Brian,

 

I will set up the single model by adding new new surface reactions to the dataset and I will get Kf and nf in sorption readings. Sections you mentioned explain exactly whay you post it before.. Conclusion: Create a new template in TEdit for model with SpecE8 implies working with datasets.

 

Once again thanks a lot for your help

 

Regards,

Juan