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pavanpec30

Smectite dissolution with Sulfuric Acid

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Hi,

 

I'm quite new to Geochemist's workbench and I have been trying to model Smectite and Kaolinite dissolution in the presence of H2SO4. The aim of my modelling is as follows

 

1) Phase diagram with different Smectite minerals that can form (pH on the X-axis and Activity of H2SO4 on the Y axis).

 

2) Time dependent dissolution of Smectite and Kaolinite when a fixed amount of H2SO4 is added to a soil sample containing Smectite and Kaolinite minerals.

 

I have had little success in trying to model the above mentioned using Act2 and GSS respectively. It would be great if someone could help me a walk-through on how to model the above mentioned.

 

Thanks,

Pavan Akula

 

 

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Hello Pavan,

 

You could certainly construct a diagram in Act2 with pH and log a H2SO4 axes, but I’m not sure how meaningful it would be. There aren’t any S-bearing smectite minerals that I’m aware of. If you’re interested in predominant Al-species, though, a plot that shows predominance fields of free Al+++ ion and complexes like AlSO4+ could be useful. For smectite stability in general, you might draw a diagram with axes like pH, the activity of species like K+, Ca++, or Mg++, or perhaps an activity ratio. If you look at a reaction like Saponite-Ca + .165 Mg++ = .165 Ca++ + Saponite-Mg, for example, you can see how increasing the activity of Mg++ would favor the forward reaction. Section 5.1, Diagram calculation, in the GWB Essentials Guide has some examples of aluminosilicate stability diagrams that might be useful to you.

 

You can use SpecE8 to determine the saturation state of smectite minerals in a given fluid or figure the composition of a fluid in equilibrium with a particular smectite. If you’d like to simulate reaction processes, though, you’ll need the React program, which is included in the GWB Standard package. And for time-dependent mineral dissolution, you’ll need to set up a kinetic reaction path. For more information, please see section 4.1, Setting kinetic reactions, and 4.2, Kinetics of precipitation and dissolution, in the GWB Reaction Modeling Guide. If you’d like a demo of the Standard package, please write a note to sales@gwb.com.

 

Bests,

 

Melika Sharifi

Aqueous Solutions LLC

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I have been trying to model the reaction of Sulfonated oils (which consists of 99.8% H2SO4) with Na-Montorillonite. I have added Na-Montmorillonite to the database and I have been having difficulty to find the database parameters for H2SO4. Do you have any recommendations on where to get H2SO4 parameters that I can use in my database?.

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Dear Pavan,

 

The thermo.com.v8.R6 thermo dataset has data for H2SO4(aq) at 25 C. You could either use that dataset, or look into the literature for its log Ks at other temperatures and edit your dataset using TEdit program. You may find some tutorials on editing thermo datasets on our website useful.

 

Please note that unless you are dealing with super acidic conditions (i.e. negative pH), you don't need to worry about H2SO4(aq) data since it becomes important only at very low pH.

 

 

Bests,

Melika

 

Melika Sharifi

Aqueous Solutions LLC

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Hi,

 

Thank you for the reply. I have been trying to run a speciation reaction for Na-Montmorillonite(MgCa) in my React module and I end up with a high residual error. The data for the input is an exact replica of the thermodynamic database which was already added to TData.

 

For e.g. If I input the molar concentration (the coefficients of phases in the reaction - refer to attached file: 1_Montmorillonite_database) from the database

 

Al+++ = 1.66 mol/l

Ca++ = 0.17 mol/l

Mg++ = 0.34 mol/l

etc.,

 

I end with a high residual error. My question is why does the above mentioned reaction does not show that Na-Montmorillonite (MgCa) is not being favored at equilibrium?

Also, how will I be able to see the Minerals that will form at equilibrium through Gtplot.

 

Thanks,

Pavan Akula

post-12333-0-15010700-1495043927_thumb.jpg

1_Volclay_Model.rea

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Hi Pavan,

 

Thanks for your message. We looked into your script, and noticed a few problems with the way it is set up:

 

1. In the basis pane of React, you set your initial system, and in the Reactants pane you define the process that alters it (i.e. the reaction path)

2. In the Basis pane, you need to enter your actual water analysis and not the stoichiometric numbers from Montmorillonite reaction. (e.g. concentration of elements/species in your initial system).

3. Finally, if you are interested in knowing the Log Ks for Montmorillonite reaction, you can use Rxn app which calculates a reaction’s equilibrium constant at a temperature of interest.

 

Hope this helps.

 

Bests,

 

Melika Sharifi

Aqueous Solutions LLC

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Hi,

 

Thank you for the reply. I have been trying to come up with a stability/phase diagram for Na-Montmorillonite (refer attached file). I have not had any luck in generating a phase diagram that includes quartz and Na-Montomorillonite in the same diagram. My query is as follows

 

1. Can I produce a Phase diagram using Act 2 for the attached file which includes Si compounds (e.g. Quartz) and Al Compounds (e.g Gibbsite) in one diagram.

 

I was able to generate one phase diagram with Al+++ as the diagram species and another one with Quartz as the diagram species. I would like to combine both species as stated above. Please let me know if there is a work around.

 

Thanks,

Pavan Akula

 

8_Volcay_MgNa_H4SiO4vsAl_Alcompounds.ac2

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Dear Pavan,

 

Please, attach your custom thermo dataset so we can take a look at your Act2 script.

 

Thanks,

Melika Sharifi

Aqueous Solutions LLC

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Hi,

 

The size of the database is too big to attach it here. I can share it via google docs if you can provide me with an email id.

 

Thanks,

Pavan Akula

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Hi Pavan,

 

You can use support@gwb.com to either e-mail it or share it with us.

 

Bests,

Melika Sharifi

Aqueous Solutions LLC

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Thank you. I have sent the database to support@gwb.com.

 

Thanks and Regards,

Pavan Akula

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Dear Pavan,

 

Thanks for attaching your script and sending your thermo dataset. We looked into your script, and found a few problems with the way it is set up:

 

1. Act2 diagrams show the predominance of aqueous species and stability of minerals for the “diagram species” you choose in the “Basis” pane on activity and fugacity axes. In the “in the presence of” field, you choose the ligands that are in equilibrium with the system and may make complexes with the diagram species, but every field in the diagram needs to be formed from the "diagram species". For example, if you choose Al+++ as the basis species, as you did in your script, only species with Al will be shown on the plot (i.e. there is no Al in quartz, and you won’t be able to see that on the plot). You should choose either Al or H4SiO4 as the “diagram species” and then swap in the mineral of interest for that species (e.g. Gibbsite for Al, or Montmorillonite for H4SiO4). Whichever you did not choose as the “diagram species”, you can add to your system as “in the presence of field” considering it is in equilibrium with your system all over the plot.

 

2. On “axes” field, you can choose activity ratio of the cations present (e.g. Na+/Mg++) in the system or Eh/pH depending on what you are looking for.

 

3. Looking at your thermo dataset, we noticed that there are three basis species for Si (SiO2(aq), H4SiO4(aq), and H4SiO4). You need to choose one of them, and make all reaction in your dataset in terms of that one.

 

Bests,

Melika Sharifi

Aqueous Solutions LLC

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Dear, pavanpec30

Hello, this it Jeonghwan Hwang, i'm new to GWB.

I'm interested in Montmorillonite-illite diagenesis and want to make a phase diagram.

Unfortunately, i cannot find any similar mineral as montmorillonite in GWB.

Can you help me to find the montmorillonite? 

Thank you

 

Sincerely, Jeonghwan Hwang

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