Act2 General Questions

[Paige]

Hello,

I am trying to recreate a figure from two papers that used Act2 to determine the stability fields of certain zeolites, both of which I have attached to this thread. I am very new to this program and was wondering if I could get some general questions answered. I've looked through the guides, and if I've missed the answers to these I apologize, but I was wondering:

1. What do the "diagram species" and "in the presence of" boxes refer to exactly? 

2. How do I add minerals to the database that I need for my research? I know analcime is in there, but it is missing phillipsite and chabazite. 

3. Is there anything I need to know when making these diagrams?

I know how to add in the x-y axis as they are in these figures, but when it comes to "diagram species" and "in the presence of" I'm not entirely sure what it means. Right now, I know that for my purposes Log a H2O = 1 and Log a SiO2 = -3.7. Does SiO2 go into the "in the presence of" box? I am mostly interested in zeolites, and some authigenic feldspar, so I am just curious how those would fit into these diagrams with the inputs provided in Act2. 

[Jia Wang]

Hello Paige,

Here are a few quick suggestions to help you get started:

With the "diagram species" selection, you choose the main species for which you want information. In this field, you can choose to select an aqueous species, mineral, or gas to diagram. The "in the presence of" field is used to modify the form of the main species by adding species and minerals that the main species can react with. 

If a mineral is not available in an existing database, you can edit that database to add the reaction for your mineral of interest. There are a couple of ways to do this. I  suggest using TEdit, a built GWB thermodynamic dataset editor. The second way, which I don't recommend until you are comfortable with editing thermo datasets, is to use a text editor. TEdit in GWB 2021 has useful error management features that check for common mistakes (e.g. mass imbalance, charge imbalance) and trigger warnings before saving.

If you are trying to match these diagrams, I would suggest checking the equilibrium constants in the database against those used in the paper. I think a good place to start is to work through some examples in section 5.1 of the GWB Essentials User guide. In particular, I think you might be interested in the aluminosilicate stability diagram. 

In general, the GWB considers all phases and species in the thermo database. In some cases, you might have to suppress more stable minerals that are not observed in your system so that less stable minerals can form.

If you need further help with troubleshooting, please attach the input file for Act2 and your modified thermo dataset so we can take a closer look. 

Hope this helps,
Jia Wang

[Paige]

Thank you for getting back to me, so I've been messing with the program some more and I am getting closer I think but I just want to verify I am not missing anything. I've attached my most recent model to this post with the input I did to achieve it. I suppressed everything except the minerals I am interested in (Albite is also included in this diagram although not showing up at stable with these conditions).

I guess my main question is, I noticed the Yucca Mountain database that is included in the installation includes thermo data for each of these minerals I am interested in and so I am using this to achieve this diagram. Can these log Ks values reported for these minerals at various temperatures be extrapolated for my area of interest? I am also looking at a caldera volcano similar to Yucca Mountain that underwent alteration by fluids of some type, so I am assuming reactions would be the same for the minerals that are listed in this database. The issue is that the papers I am looking at do not give equilibrium constants and I do not think there are any reported for my area specifically. The only information given from these papers is that Log a H2O = 1 and Log a SiO2(aq) = -3.7 for my system. 

In addition, are there any big things to include for activity-activity diagrams that it seems I am missing here in my input file?

[Jia Wang]

Hello Paige,

In general, I would advise caution when extrapolating log K's for temperature beyond the range of validity prescribed for the reaction of interest. The further you extrapolate outside the range prescribed, the less accurate the values become. You can identify the temperature range for the dataset in the Tables pane in TEdit. Some reactions may not have equilibrium constants for the full range. 

If you are interested in using the Yucca Mountain dataset for you work, I would advise reading through the documentation for this database carefully before doing so. This dataset follows the Harvie-Moller-Weare formalism of the Pitzer equation, designed for modeling high ionic strength fluids. 

Jove-Colon, C., T. Wolery, J. Rard, A. Wijesinghe, R. Jareck, and K. Helean, 2007, Pitzer database development: Description of the Pitzer geochemical thermodynamic database data0.ypf.R2. Appendix I. In In-Drift Precipitates/Salts Model, Report ANLEBS- MD-000045 REV 03, DOC.20070306.0037, Las Vegas, Nevada: Sandia National Laboratories.

You can find out more about the various thermodynamic datasets installed with the GWB in chapter 2.3 of the GWB Essentials Guide. 

It would be difficult to troubleshoot the diagrams if you cannot be certain that the log Ks used in the database is the same as the one used for creating the diagrams in the paper. I would suggest contacting the corresponding authors to clarify what parameters were used in calculating these diagrams and the procedures used. 

Hope this helps,
Jia