Geochemist's Workbench Support Forum

# [OLD] Diagramming Nepheline

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From: John Pareizs

Subject: diagramming nepheline

I am looking for advice and guidance on using Act2 for activity diagrams. I am running into swapping problems. My solution is basically Na+ and NO3- with a pH around 12. My x-axis is SiO2(aq), and y is Al(OH)4-/H+. I am interested in Nepheline (among others). I have tried diagramming two ways getting two results. Which is â€œrightâ€??

Diagram 1

swap Al(OH)4-/H+ for Al+++

swap Nepheline for H+

specify Na+ and NO3- activities with values from React output

Diagram 2

swap Al(OH)4-/H+ for Al+++

swap Nepheline for Na+

specify NO3- activity from react output

specify pH=12

One other question is what does the Act2 diagram command do? For example, what is the difference (or why is there a difference) between â€œdiagram Nepheline on....â€? and diagram Na+ on...â€?, with all other things equal?

From: Craig Bethke

Subject: Re: diagramming nepheline

I can't really answer your first question since you don't describe what problem you are trying to solve or give complete information about â€œDiagram 1â€? and â€œDiagram 2â€?. As a stab, you might be trying to understand the stability among sodic aluminosilicates as a function of silica and alumina activities in solution at pH 12. In that case, try something like:

T = 300

swap Nepheline for Na+

swap Al(OH)4- for Al+++

diagram Nepheline on SiO2(aq) vs Al(OH)4-

pH = 12

X -6 0

Y -6 0

As for what the â€œdiagramâ€? command does, that's simpler. When you create a diagram, you are considering the reactions among all species that (1) contain the species you specify on the â€œdiagramâ€? command, and (2) can be made up from that species plus or minus the species on the two axes, plus or minus water, and plus or minus any coexisting species you specify. In the above example, the program considers all species and minerals that can be made up of Nepheline +/- Al(OH)4- +/- SiO2(aq) +/- H2O +/- H+.

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