kristeng

Got it. Thanks very much for clarifying.

Hi Brian, Thanks for your response. I increased the biomass and it dramatically changed my results! I do believe that was the correct file - I attached the output. I had misread the results. I was looking at spp totals for SO4-- which was 1018 mg/L, leading me to believe a drop of 400 mg/L had occurred in the first step of the reaction; however, I realize now that I had not accounted for other SO4 spp like CaSO4 and MgSO4. From the original basis totals I can see that the SO4 conc did not decrease. However, I see the change now that I increased the biomass concentration. Can I constrain the amount of Fe (Fe2+ + Fe3+) in the system and have it equilibrate with FeS? Would I do that as I described above in my first post? Thanks for your help.

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