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Problems with pyrite in Act2


Guelph_Alex
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Hi,

I found a problem when looking at pyrite species in Act2. At 25°C, there seems to be no issue, but as soon as i change to a different temperature, higher or lower, by any amount, even 1°C, the diagram turns from 2 species, to just pyrite. If anyone could explain why this is happening it would be appreciated. Thanks

 

Alex

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Hi,

I found a problem when looking at pyrite species in Act2. At 25°C, there seems to be no issue, but as soon as i change to a different temperature, higher or lower, by any amount, even 1°C, the diagram turns from 2 species, to just pyrite. If anyone could explain why this is happening it would be appreciated. Thanks

 

Alex

 

Hi Alex:

 

This is hard to troubleshoot without seeing your script- can you attach it?

 

Regards,

 

Tom Meuzelaar

RockWare, Inc.

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Hi Alex:

 

This is hard to troubleshoot without seeing your script- can you attach it?

 

Regards,

 

Tom Meuzelaar

RockWare, Inc.

 

This is the code I used. I ran the 25°C test first then the 26 after, but any temperature other than 25 seems to give the same result.

Act2> T = 25

Act2> diagram Pyrite on Eh vs pH

Act2> x frp, 0 to 14

Act2> x from 0 to 14

Act2> y from -1 to 1

Act2> a Pyrite 1

Act2> go

Act2>

Act2> T = 26

Act2> go

Act2>

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This is the code I used. I ran the 25°C test first then the 26 after, but any temperature other than 25 seems to give the same result.

Act2> T = 25

Act2> diagram Pyrite on Eh vs pH

Act2> x frp, 0 to 14

Act2> x from 0 to 14

Act2> y from -1 to 1

Act2> a Pyrite 1

Act2> go

Act2>

Act2> T = 26

Act2> go

Act2>

 

Alex:

 

What version are you using?

 

The above script has a few configuration problems. The following is a working configuration, and does not show the temperature discrepancy:

 

data = "c:\program files\gwb\gtdata\thermo.dat" verify

temperature = 24 C

swap Pyrite for Fe++

swap e- for O2(aq)

diagram Pyrite on Eh vs pH

log activity main = 0

x-axis from 0 to 14 increment 2

y-axis from -.75 to 1.25 increment .5

 

Let me know if that gets you where you want to go,

 

Tom

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I am using version 6.0.5. and i think its may be that I am not using thermo.dat, instead i am using thermo.com.v8.r6+.dat

as i needed Molybdenum species in my diagrams. thanks

 

Alex:

 

What version are you using?

 

The above script has a few configuration problems. The following is a working configuration, and does not show the temperature discrepancy:

 

data = "c:\program files\gwb\gtdata\thermo.dat" verify

temperature = 24 C

swap Pyrite for Fe++

swap e- for O2(aq)

diagram Pyrite on Eh vs pH

log activity main = 0

x-axis from 0 to 14 increment 2

y-axis from -.75 to 1.25 increment .5

 

Let me know if that gets you where you want to go,

 

Tom

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I am using version 6.0.5. and i think its may be that I am not using thermo.dat, instead i am using thermo.com.v8.r6+.dat

as i needed Molybdenum species in my diagrams. thanks

 

Alex:

 

Thanks- I can reproduce it now. The reason you're getting Pyrite stability across the diagram at T=24 and T=26 is that you haven't added the sulfate component to your system. You've defined a diagram for Pyrite by swapping it in for the iron component, but your system needs to also contain sulfur in some form. If you look at the output diagram (Run - View - .\Act2_output.txt) you'll notice that the system only considers Fe(SO4)2- as an aqueous diagram species. In thermo.dat, this works fine, as this species has log K values defined at every temperature interval. However, in thermo.com.v8.r6+.dat, the Fe(SO4)2- aqueous species has a log K defined only at 25C.

 

If you add the sulfate component to your diagram, Act2 will take a variety of Fe-S aqueous species and minerals into consideration.

 

I hope that helps,

 

Tom

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