Jump to content
RockWare Support Forum

Recommended Posts

Hi

I am trying to draw the act2 for Fe species at different pH. The problem is that not all of the species are showing in the diagram. The species that are appearing if l click the log icon are:

Subdiagram #7: Fe+++ with K+, CaOH+, Brucite, Na+, Al(OH)4-, Mn(OH)2(am)

Loaded 14 species and minerals:

Fe+++ Fe(OH)2+ Fe(OH)3 Fe(OH)4-

Fe2(OH)2++++ Fe3(OH)4(5+) FeOH++ Fe(OH)3(ppd)

Ferrite-2-Ca Ferrite-Ca Ferrite-Mg Goethite

Hematite NaFeO2©

Subdiagram #8: Fe+++ with K+, Portlandite, Brucite, Na+, Al(OH)4-, Mn(OH)2(am)

Loaded 14 species and minerals:

Fe+++ Fe(OH)2+ Fe(OH)3 Fe(OH)4-

Fe2(OH)2++++ Fe3(OH)4(5+) FeOH++ Fe(OH)3(ppd)

Ferrite-2-Ca Ferrite-Ca Ferrite-Mg Goethite

Hematite NaFeO2©

All of these minerals are not appearing in the plot. Can you please help me to sort this problem. Please find attached the act2 file.

Regards

Fe-pH.ac2

Share this post


Link to post
Share on other sites

Hi,

A few things. The species listed after Subdiagram #7,8 etc. are the Basis species for that particular subdiagram. You have chosen to account for the speciation of all your complexing species. The Ca++ component, for example, appears as CaOH+ in #7 and as Portlandite in #8. This does not mean that CaOH+ or Portlandite are present in any amount, however. It simply means that any reaction within that subdiagram with Ca++ is written in terms of CaOH+ or Portlandite. If you scroll down a little bit (from Subdiagram - Basis species - Species and minerals in main system - Line equation - Main Diagram) you will find the species and minerals which actually have predominance over the subdiagram, and will appear in the main diagram.

Keep in mind that Act2 generates predominance diagrams, meaning only the most stable mineral or species will appear. Furthermore, you are diagramming the Fe system, so every mineral or species on the diagram must have Fe in it. You can use SpecE8 or React to calculate the concentrations of other aqueous species, mineral saturation, etc if that is what you are interested in. Finally, I noticed that you have decoupled several Fe and Mn redox pairs. Because you decoupled Fe+++/Fe++ and chose to diagram Fe+++ without specifying any Fe++, you have prevented Fe++ minerals and species from being considered in your diagram. You should make sure this is what you really want. Let me know if you want anything explained better.

Hope this helps,

Brian Farrell

Aqueous Solutions LLC

Share this post


Link to post
Share on other sites

Hi

Thanks very much for the assistance on ACT2. I have another question on the drawing an ACT2 diagram for Al species against pH. I know that at pH greater than 11 the most stable mineral phase that exists is ETTRINGITE but on my diagram the phase that is predominate is Al(OH)4-. Is there a way to edit the database to suit what I want to depict in the diagram.

Share this post


Link to post
Share on other sites

Hi,

Sure you can edit the database if you feel changes are warrented. Take a look at the Appendix to the GWB Reference Manual for info on editing thermo datasets. You might remove minerals or species which appear in the high pH region of your plots, or change the stability (log K value) of Ettringite. You can also do this from within GWB in a less permanent fashion, using the Suppress and Alter commands.

A few things to consider before doing this, though. Do other minerals appear on your plot? If not, make sure that the field for "minerals" is checked in the View dialog box. Also make sure that Ettringite is not undersaturated in your system, and that it is indeed the most stable Al species.

Hope this helps,

Brian

Share this post


Link to post
Share on other sites

×