webmaster Posted December 26, 2004 Share Posted December 26, 2004 From: Gregg Jones Subject: stability of pyrite I'm trying to determine if pyrite in limestone in the Floridan aquifer is stable under the set of ground-water conditions described below. I used ACT 2 and plotted the log of the activity of the sulfate/sulfide ratio vs pH. Pyrite falls comfortably within the pyrite stability field and I want to verify that I've set up the input correctly. Here's my input data for ACT 2: Diagram Fe++ on O2(aq) vs pH Swap SO4--/S- for O2(aq) Log a SO4-- = -2 Log a Fe++ = -7 Speciate SO4-- over X-Y x from 0 to 14; y from -25 to 30. go Some additional info: pH = 6.99 Sulfate Conc. = 1,526 mg/l Sulfate Activity = 1.59 X 10 -2 Sulfide Conc. = 14.5 mg/l Sulfide Activity = 1.51 X 10-4 Iron Conc. = 0.065 mg/l Iron Activity = 6.7 X 10-7 Using release 3.0 From: Craig Bethke Subject: Re: stability of pyrite The good news is that it's a safe bet that pyrite is thermodynamically stable in a water of neutral pH containing ferric iron, sulfate, and sulfide. I suspect the diagram you propose is not exactly what you have in mind (it's hard to know: there is no species S-; perhaps you mean HS-?). To determine if a diagram is appropriate for a purpose, first consider what reactions you wish to consider. After you've made the diagram, select Run -> View -> Act_output.txt and verify that those reactions were used to construct the diagram. Quote Link to comment Share on other sites More sharing options...
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