Looking for a case file for zinc

[DY OUI CMT]

Want to try to generate Eh-pH diagrams for zinc using Act2. Looking for a case file (*.ac2) that considers more species/minerals.

[Brian Farrell]

Hi,

 

There are at least a couple factors that affect what species appear in your Eh-pH diagrams. The contents of the thermo dataset currently loaded by the program will be one limiting factor. Another is how you set up your chemical system: the Basis entries and temperature.

 

I would start by looking into what species are loaded into the program by going to Config -> Show. Or you can view the thermo dataset directly by going to File -> View and selecting the thermo dataset. If you're running GWB9 or older, the dataset will open in Notepad. If you're using GWB10, the dataset will open in TEdit, the graphical thermo data editor. In TEdit, you can filter on a particular species, like Zn++, to see all the Zn-containing species. Thermo.tdat, for example, contains some chloride and phosphate complexes and some sulfide minerals like sphalerite. You could consider these in your Act2 diagram by adding a complexing ligand like Cl-, HPO4--, or SO4-- to the "in the presence of" section. If the dataset doesn't have some of the minerals or species that you're interested in, you can modify it by adding data from the literature, or from another thermo dataset. Or you can load a different thermo dataset instead.

 

You may also investigate whether it's necessary to suppress certain species (to give less stable species a change to form) or to create what's called a mosaic diagram (allowing complexing ligands to speciate over the x and/ or y axes). See 3.53 in the GWB Reference Manual for details of the suppress command in Act2 and section 5.3 in the GWB Essentials Guide for a description of mosaic diagrams.

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions

[DY OUI CMT]

Looks like I need to add species to the dataset. Is there an online tutorial that you can refer me to? Thanks.

[Brian Farrell]

Hi,

 

If you’re using GWB10, you can find some tutorials on adding species to a thermo dataset using TEdit here. You can add the reaction for a species as you see it in the literature and TEdit will rebalance the reaction in terms of the dataset’s Basis species. There’s also a tutorial on using copy and paste or drag and drop to import species from one thermo dataset to another. Thermo_minteq.tdat, for example, includes some Zn hydroxy species that may be of interest to you. Chapter 9, Using TEdit, in the GWB Essentials Guide has a more complete description of the TEdit program.

 

If you’re using GWB9 or an earlier release, you’ll need to edit the dataset in a text editor like Notepad. The easiest thing to do is to copy the entry for a similar species or mineral, paste it into Notepad, then edit whatever needs to be changed. You’d obviously change the name and mole weight of the species, as well as the “species in reaction” and log K at one or more of the principal temperatures. You can only list 3 “species in reaction” on a single line, so if there are more you’ll need to go on to the next line. If you don’t know the log K for a particular temperature, enter a value of 500 for the log K. The final step is to update the “count” of minerals, aqueous species, etc. in the dataset for every new species that you add. Here’s an example of adding a mineral to a thermo dataset in which you need to rebalance the reaction to account for the basis and redox species in the thermo data.

 

Hope this helps,

Brian