[OLD] Decoupling HS-

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From: Paul Foellbach

Subject: decoupling HS-

I attempt to model the mixing between seawater and brine. I would like to realize a Equilibrium and Disequilibrium model. Equilibrium of HS-: If I model the Sulfate-Sulfid-Equilibrium (all couples of database are coupled), the resulting dominant aqueous S-Species is H2S(aq) (ca. 2 mmolal). Disequilibrium of HS-: If I decouple HS- to inhibit the sulfate-sulfide equilibrium, HSO4 is the dominant (ca. 2 mmolal) aqueous S-species. The resulting S-Metal-minerals from equilibrium calculation are Sulfides. The resulting S-Metal-minerals from disequilibrium calculation are Oxides and no sulfides. I can't understand the dependance of S-speciation on Dis- or Equilibrium conditions ? The initial S in solution is speciated as H2S(aq). Why does the speciation of S in solution depend on equilibrium or disequilibrium at the first calculation (Equilibrium or Diseqilibrium) step. In my opinion the INITIAL (first step of equilibrium calculation) concentration of H2S(aq) = 2 mmolal in a solution doesn't change neither at equilibrium nor at disequilibrium calculation of HS- and SO4-speciation, because at the first step H2S(aq) is concentrated at 2 mmolal and not 2 mmolal HSO4. I would appreciate any help to understand these points.