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dong5600

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  1. Brian: I just found H+ can also pair with e- as the pair for Eh or pe. However, when choosing it, it was swapped out of the pH basis and pH cannot be set. A little confused. Thanks! Yiran
  2. Hi, Brian: Thanks a lot. For the last message, what I meat was the state and the forms of iron in my reaction system. For example, lepidocrocite (a kind of FeOOH) was used as the electron acceptor, hydrogen was used as the electron donor. When the reaction occurs, I don't feel the Fe(III) and Fe(II) ratio can be simply expressed as Fe+++/Fe++ because the majority of Fe(III) stay in the solid phase. However, when using diagram species for lepidocrocite <--> Fe++, I could only define activity as 1 but could not input Fe(II) concentrations (e.g., Fe++=10 mM). Which forms for these iron species I should set to reflect the conditions in my reaction system? Thanks! Yiran
  3. Brian: Thank you so much. Your suggestion is very helpful. Just to follow up, you mentioned some alternative species "such as O2(g), the e-, H2(aq), H2(g), or even activity ratios, such as Fe+++/Fe++". So far, I only found choice of Eh or pe under O2 pair (maybe I miss something else. I am wondering if there is another redox pair better fitting anaerobic condition. Is e- available for pairing with H2? Also, for Fe+++/Fe++, can we do this for pairing with ferric solid mineral with Fe++ as mineral is way less soluble than Fe+++ itself? Thanks a lot! Yiran
  4. Dear GWB: I have a question about making Eh-pH diagram to predict iron secondary minerals formed during iron reduction under anaerobic condition. My questions include: 1) When we choose the pair for Eh, is oxygen-e- the only choice? I could find other selections for Eh, but oxygen does not seem correct for anaerobic reaction, which typically exhibit negative Eh values. 2) For some of the solid phases, the ones showed up in the Eh-pH diagram were not observed in our study, while some of our observed ones did not appear. Is there any way I can check, modify or add some mineral information? Is solubility the only information needed for such analyses? Any suggestion is highly appreciated! Yiran
  5. Thanks a lot, Brian. I will check it. The second solution sounds reasonable to me. I used the 25 degree temperature logK for green rust, but it did not show on the secondary minerals after I calculate the saturation index. I think what you mentioned may explain it. Will try again and thanks a lot! Yiran
  6. Brian: Thanks a lot for your suggestion. I will search for more thermodynamic information. For the logK you suggested, I have another question for it. I was trying to set the logK for one of the new minerals (carbonate green rust), since I could not find H and S for it, I was not able to use Van't Hoff equation to calculate logK at other temperatures. So, I input the value at 25 degree and left others 500. When I was calculating for the reactions at 37 degrees, the system reported errors and did not give any result. Is that mean the setting temperature have to be the same as the reaction temperature? Thank you again! Yiran
  7. Hi, Brian: I have a follow-up question about calculating the equilibrium constant for the custom minerals. I did some calculations of lepidocrocite based on the Van't Hoff equation, the thermodynamic values I found for this mineral and other components for the dissolution reaction FeOOH+3H+--->Fe+++ +2H2O. The calculated Keq seems very small (logKeq=-0.00046 at 25 degree C), much lower than the value reported for dissolution constant (logKsp=log([Fe+++]/[H+]^3)) reported in literature (logKsp=1.39 reported in Schwertmann, Solubility and dissolution of iron oxides, Plant and Soil, 130, 1-25). For this reaction, my understanding about the Keq and Ksp is that they are the same. I am curious which values I should use. Because for another mineral I was planning to add, there is no solubility information but free energy, so I have to use the energy method to calculate equilibrium constant and am concerned about the accuracy. Please advise and thanks a lot! Yiran
  8. Thank you, Brian. It is very helpful and your answer is applicable to my another question. Yiran
  9. Dear all: I am trying to calculate secondary mineral formation in the microbial iron reducing systems. One of the minerals we are interested is green rust with formula [Fe2+4Fe3+2(OH)12][CO3]·3H2O, which is not in the mineral list for GWB. The GWB has Fe(OH)2 in the system, which is also another kind of green rust, but is different from what we observed. Does anyone has suggestion how to create it ([Fe2+4Fe3+2(OH)12][CO3]·3H2O) in the system so that it can be calculated? Millions of thanks! Yiran
  10. Hi, Brian: I want to calculate saturation index for the secondary minerals formed from reduction of lepidocrocite (gamma-FeOOH). I found the logK information for different minerals in the thermo file, but lepidocrocite is not there and the logK values were given to different temperatures (e.g., 0-300 degree C) in the system. Now, I found solubility for lepidocrocite at room temperature in another paper, is there any way I can integrate such information into the system and fill the logK values for other temperatures? Please advice. Thanks a lot! Yiran
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