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FeS(ppt) and Mackinawite
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Topic: FeS(ppt) and Mackinawite (Read 3660 times)
Model1
Contributor
Posts: 6
FeS(ppt) and Mackinawite
«
on:
11/02/15 12:28 »
Dear,
What is exactly the difference between FeS(ppt) and Mackinawite ?
Is the first one more amorphous ?
Thank you.
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dlparkhurst
Global Moderator
Posts: 4030
Re: FeS(ppt) and Mackinawite
«
Reply #1 on:
12/02/15 03:30 »
I suspect that the ppt refers to freshly precipitated FeS, and as such would possibly be amorphous. The log K is definitely larger than for Mackinawite, which indicates it is less stable.
You may be able to find the references in the WATEQ4F manual (Ball and Nordstrom).
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mukherjeeindrani09
Frequent Contributor
Posts: 10
Re: FeS(ppt) and Mackinawite
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Reply #2 on:
26/09/23 20:34 »
The saturation index for FeS(ppt) is -128 for me. How can a precipitated mineral be in a undersaturated condition?
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dlparkhurst
Global Moderator
Posts: 4030
Re: FeS(ppt) and Mackinawite
«
Reply #3 on:
26/09/23 20:53 »
I suspect PHREEQC is simply calculating the saturation index for the SOLUTION you defined. You need to adjust the SOLUTION definition, or use EQUILIBRIUM_PHASES to have a solution that is in equilibrium with mackinawite.
Mackinawite is pretty insoluble. Small changes in pe or concentration can cause large changes in the SI.
Consider the results of this calculation:
Code:
[Select]
SOLUTION
pe 4 Mackinawite 0 10
Na 2
S 1
Fe 1e-3
END
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FeS(ppt) and Mackinawite