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Hi there, I am learning how to model sulphate reduction in hypolimnetic waters of a circumneutral pit lake. I have used the sulphate reduction set up from the Bethke textbook example for the aqufier (33.2). I have added acetate and balanced with Na, and decoupled CH3COO-/HCO3- and HS-/SO4--. I have the Fe++ concentration swapped for pyrite (ideally mackinawite but I have not yet updated my database) as I thought this would control Fe++ concentration under sulphate reducing conditions. I am perplexed as to why the sulphate concentration decreases only by ~400 mg/L (initial 1400 mg/L, final 1000 mg/L). In the Bethke textbook it indicates that sulphide in solution will inhibit the SRBs, so perhaps this is why. However I would assume this would be buffered by sulphide minerals. In addition I do not have a huge amount of sulphides precipitating. Is there an error in the way I have set up the basis or the reactants? If I want to indicate that pyrite or mackinawite controls the Fe concentration, but also specify a starting Fe concentration (total Fe, I do not know spp) - can I do this? Do I just specify Fe (Fe++ as Fe) in the basis and then add a small amount of FeS in reactants? I look forward to responses if anyone has insight here. Regards, Kristen Sulphate reduction example.rea