srikaush

Hi, I am trying to obtain a speciation plot for a solution containing FeCl2 (ferrous chloride) and NaHCO3 (sodium bicarbonate) using the student edition GWB 11. I have experimental data for pH of this solution as well. While entering the basis species, I don't have the option of entering HCO3- species. I only have the option for CO3(2-) [carbonate] species. I would also like to calculate the supersaturation of this solution with respect to magnetite. What would be the best way to come up with an accurate speciation plot for these conditions? Any help would be appreciated. Thanks!

Hello, I have downloaded the specified demo of GWB standard and I have been trying to use the React module for simulating my experimental set up. However, I have not had luck with it. I am still confused as to how I can specify two separate fluids (with different aqueous species and pH @ room temperature) that come together at a particular temperature (different from room temperature) to react. Please let me know how I can do this. I would like to know the saturation index with respect to magnetite. Thanks in advance! Kaushik

Hello, I am just reposting as I still need help on this. Any help is appreciated. Thank you. Kaushik

Hello Katelyn, I have attached the gss files of the two cases I mentioned in my previous post. The first is the case I am essentially interested in. The second case is something that I tried that yielded supersaturation w.r.t. magnetite. Howevemr I don't feel the second case is accurate for definition of my system. Thanks in advance for the help! Kaushik SolMix_Fe(II).gss SolMix_Fe(III).gss

Hello, I am trying to calculate the supersaturation with respect to magnetite of two solutions after they are mixed. The first solution contains only ferrous chloride while the second solution consists of sodium nitrite (that helps with oxidation of Fe(II) to Fe(III)), acetic acid and ammonium hydroxide. Now, when I feed my experimental conditions into the GSS worksheet (with measured pH of each solution) and mix them and then speciate the mixture, I do not get supersaturation values with respect to magnetite and the reason is attributed to the absence of Fe(III) in the initial solutions. I have also tried decoupling Fe(II) and Fe(III) but to no avail. Is this because the nitrite to nitric oxide reduction reaction in some way disregarded in this set up of conditions? Another related issue- When I ignore the sodium nitrite in the second solution and instead assume all of it is used up to oxidize corresponding concentration of Fe(II) and I define the first solution as a mixture of Fe(II) and Fe(III), I get a supersaturation with respect to magnetite albeit with a charge imbalance. I would like to know if the charge imbalance makes the speciation and supersaturation numbers invalid. Any help is appreciated! Thanks in advance. Kaushik

Hello Katelyn, Thank you once again for your suggestion. I was able to fairly reproduce the literature data using minteq. However, I have a doubt that is related to my previous query about charge imbalance. I was able to generate these plots by defining basis species as just Fe(II) and H+(for pH) and nothing else. Consequently, there was no charge balance in any of my calculations. Is this the right method to speciate aqueous systems? Isn't electroneutratily an important requirement for thermodynamic modeling? I discussed this approach I have been using in the software with my advisor and he is not convinced this would give me any meaningful analysis. However, as I mentioned I was able to reproduce the literature data fairly closely. I guess my question is how is this possible without charge balance in the solution? Kaushik

Hello, I have cross checked and it looks like the references match the database I used. I used the thermo.tdat default database on GWB. The reference there points to "The hydrolysis of cations" by Baes and Mesmer (1976) and the plot from literature I had attached in my previous post is from that very text book. Please let me know what I have done wrong as I am unable to match the plots. Thank you. Kaushik

Hello, I followed your suggestion and did the speciation without adding the charge balance and tried to speciate a 0.001 molal Fe(II) solution at 25 C to try and reproduce existing data from literature. However, I get a different result to what is seen in literature. I have attached the speciation file, excel plot from the speciation at various pH and the data from literature. The species labelled (1,0), (1,1), (1,2) and (1,3) in the literature data correspond to Fe++, FeOH+, Fe(OH)2 and Fe(OH)3(1-) respectively. Please let me know what I have done wrong. Thank you. Kaushik Fe(II) speciation @ 25C.xlsx Fe(II) speciation @ 25C.sp8

Fe(II) speciation at 90C.sp8 Hello, Thanks for your response. I followed the steps in the forum. However I encountered an error when I hit a pH of 10 (working up from 2) when I tried speciation of an Fe(II) solution at 90 deg. C . The error reads " Residuals too large, 684-th iteration..." . I have attached my speciation file. Please let me know what I have done wrong. Thank you.

Hello, I am trying to plot a speciation diagram with Fe(II) in solution over a wide range of pH. The plot essentially needs to be a concentration (of various Fe(II) species) v pH. I watched a tutorial video on youtube which goes over doing such a plot with the React module. (link below) However, since I have the student edition, this module is not available. I would like to know if this sort of a diagram can be constructed with the modules that come with the student edition. I have already tried the specE8 module. However, this lets me specify only one pH at a time. Would it be okay to use this module to run the speciation multiple times at various pH and then use another graphing software to plot the numbers I get after every individual iteration? Any help is appreciated. Thanks in advance! Youtube link with speciation tutorial using React module: