[OLD] How set a free mineral phase

[webmaster]

From: Paul Foellbach

Subject: how set a free mineral phase

I attempt to work with data of a hydrothermal fluid, that was sampled at the North Fiji Basin. I assume, that this fluid was affected by precipitation of Pyrite while sampling. Now I like to correct this fluid composition in respect to Fe and S. I would like to saturate this fluid with Pyrite. I swapped Pyrite for Fe and set a certain value of Pyrite (not free), that gives the saturation of Pyrite in this fluid. I have to set this Pyrite as a free Species. When I do this, it happens the following:

1. script with not free Pyrite:

> decouple HS-

> swap Pyrite for Fe++

> 1.00000317 kg free H2O

> free molality O2(aq) = 4.2236754e-32

> total mol H+ = .0159720092

> total mol HS- = .002

> total mol HCO3- = .0144

> total mol Na+ = .21

> total mol K+ = .0105

> total mol Ca++ = .0065

> total mol Ba++ = 5.9e-6

> total mol Mn++ = 1.2e-5

> total molality Pyrite = 4.067e-7

> total mol Li+ = 2e-4

> free molality Al+++ = 1.76591595e-19

> total mol SiO2(aq) = .014

> total mol Cl- = .233045809

> total mol Br- = .000306

> total mol B(OH)3(aq) = .000465

> total mol SO4-- = 1e-40

> precip = off

> printout species = long

React> go

 

Solving for initial system.

 

Loaded: 348 aqueous species,

177 minerals,

14 gases,

0 surface species,

16 elements,

14 oxides.

-- Warning: expected a free constraint for mineral Pyrite N-R converged in 199 its., resmax = 7.49e-013, Xi = 0.0000 Charge balance: Cl- molality adjusted from .233 to .233 36 supersaturated phases, most = Clinoptilolite-Ca No reaction path specified.

 

2. script with free Pyrite:

 

React> free Pyrite = 4.067e-7 molal

React> go

 

Solving for initial system.

 

Loaded: 348 aqueous species,

177 minerals,

14 gases,

0 surface species,

16 elements,

14 oxides.

 

*N-R didn't converge after 999 its., resmax = 0.000247, Xi = 0.0000

Largest residual(s):

Resid Resid/Totmol Cbasis

--------------------------------------------------------

SO4-- 1.325e-010 0.0002468 1.809e-011

--------------------------------------------------------

React>

 

I set exactly the value of free Pyrite to saturate this solution, but the calculation can't converge. I don't know how to set the free Pyrite for saturation.

 

From: Craig Bethke

Subject: Re: how set a free mineral phase

My guess is that the second run didn't work because the program couldn't achieve charge balance. (It actually converged to within a small tolerance.) Neither approach, however, is the correct solution to the problem of correcting the fluid composition for pyrite precipitation. To do this, take the fluid as analyzed and titrate more that enough pyrite into it (use the “react� command) to saturate the fluid. Then, after this step is complete, do a “pickup fluid� to eliminate the excess pyrite.