Plot multiple species on y-axis in Act2

[swhitman]

I'm wondering if it is possible to plot more than one species on the y-axis of an act2 diagram.  In some cases, the most important species changes with the x-axis variable (e.g., pH).  One example is attached as an image.  For aluminum, Al3+ is most important for pH <6, while Al(OH)4- is most important for pH >6.

Can a plot like this be recreated in Act2, or another module in GWB?

More generally, would it be possible to create a mosaic diagram for pH activity plots, such that the concentration of the dominant species is used for scatter data, as well as the phase boundaries in these plots? It seems like this would be a very similar concept to the 'mosaic diagrams'.

 

Thanks,

[Jia Wang]

Hello,

Act2 calculates and plots activity-activity diagrams. This class of diagrams shows the stability of minerals and the predominance of aqueous species in chemical systems. A species activity, gas fugacity, activity or fugacity ratio, pH, Eh, or pe may serve as an axis variable.

You can only vary the activity of one species on an axis at a time in Act2. To combine plots together, you would need to do so in another program.

I am not exactly sure what you mean by "such that the concentration of the dominant species is used for scatter data, as well as the phase boundaries in these plots". You can create solubility diagrams by setting the main species (e.g. Al+++) as one of the axis and varying across a range of values. For example, if you wish to create a solubility diagram of Al+++ vs pH, you can select the main diagram species as Al+++, leave activity blank. Under "on axes", set "H+" and units of "pH" for one axis and the other select "Al+++" and set your desired range. For an example of this, please see section 5.2 Solubility diagrams in the GWB Essentials Guide.

You can add species in the "in presence of" section of Act2 and allow it to speciate over the diagram axes. The main diagram will account for these speciation changes.  Scatter data on the other hand is read in from either a GSS or a text file format to plot onto your plot. The data must contain the axes variables in order for the data to be plotted. Note that the program works with activities and not concentrations. If you have concentration data, you can use GSS to calculate the activities for species (e.g. Al+++) and then plot scatter data onto your activity diagram.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

 

[Jia Wang]

Hello again,

I just want to follow up to provide some clarification. While you cannot simultaneously display two species on one axis, the equilibrium lines drawn in the diagram do use the predominant species as your x variable changes. If you construct the Al solubility diagram as described above, the predominant Al species at low pH is Al+++ and as pH increases on the x-axis, the predominant form eventually becomes Al(OH)4-. You can click on the line boundary to see the equilibrium reaction on the diagram and balance the reaction in Rxn to see the equilibrium equation plotted. Alternatively, you can open the text output file ("View Results" button on the bottom of the Plot pane) to see equilibrium equations possible for all reactions among the aqueous species and minerals in the system. In the bottom section of this file, you will find the ones used for the main diagram.

Hope this helps,
Jia

[swhitman]

Hello Jia,

Thanks for the clarification.

Some clarification of my own -- I did understand that the diagram itself used the dominant species, but I was hoping that it would be possible to smartly select corresponding data points from GSS to plot in the diagram.

For example, in the attached diagram, for pH < 6, pairs of pH and {Al3+} would plot, and for pH > 6 pairs of pH and {Al(OH)4-} would plot.

As I understand it, currently, only one variable can be plotted on the y-axis -- that is, the diagram species that is chosen in the basis pane.

As illustrated in the attached figure, there are cases where it would make sense to vary which species is plotted (as scatter points). In some cases, there are more than two predominant species to consider across a given pH range.

My current workaround for this is to make two separate diagrams: 1 for low pH conditions, and 1 for higher pH conditions.  Another workaround might be to 'trick' the software by substituting values of {Al(OH)4-} into the {Al3+} row, in a separate GSS to avoid confusion.

Sound like the answer right now is 'that's not possible', but it would be a useful option!

Hopefully that all makes sense, please let me know if it is unclear.

[Jia Wang]

Thank you for the additional clarifications. Yes, you are correct that the plot will only display scatter data based on the current axes variables. There's no way to designate the predominant species to plot. The workaround you mentioned above is certainly one strategy to address this at present. I will add your suggestion to the list of user-requested features.

Best regards,
Jia