Bill Burgos

and btw, Li2Si2O5 does appear when i generate plots in Act2 - so that's cool but i really want to examine Q/K over time in our experiments hope to hear from you soon happy thanksgiving

Hi Brian OK, I am so close to getting this to work. As I noted earlier, I found on old Bureau of Mines report that included deltaG0f(25oC) and deltaH0f for Li2Si2O5. I combined that reaction with a series of other reactions (all of which I knew deltaG0rxn and deltaH0rxn at 25oC) to get an overall reaction in the exact form of the GWB entry for Na2Si2O5. In this case, the overall balanced reaction for my new mineral entry is Li2Si2O5 + 2H+ -> 2Li+ + 2SiO2(aq) + H2O So with deltaG0overall(25oC) and deltaHoverall I was able to calculate log K values for 0 - 100oC (I just put 500.0000 into the 4 other temp entries). I copied and pasted the GWB entry for Na2Si2O5 into the top of my mineral section. I replaced Li for Na such that I changed the mineral name, its reaction products, and recalculated the MW. I also increased the number of minerals from 624 to 625. I've set all GWB programs to use this new thermo+test.data file. I've used Rxn and balanced the reaction and checked that my log K entries are there. So now I go back into GSS to +Analyte -> Calculate -> Mineral saturation, and Li2Si2O5 does not appear in my selection list. Previously I cut and pasted the Albite mineral entry and renamed it 'Albite test'. This mineral did appear in the list. If I can get Li2Si2O5 to appear I may stop bugging you for a while Cheers Bill

Hi Brian I’m trying to add a new mineral to my thermo-glass.dat file but am first going through some calculations to better understand the entries in the existing thermo.dat file. Below is the entry for the aqueous species MgOH+. MgOH+ charge= 1.0 ion size= 4.0 A mole wt.= 41.3123 g 3 species in reaction 1.000 Mg++ 1.000 H2O -1.000 H+ 12.8428 11.7908 10.5646 9.4383 8.3151 7.3806 6.5193 5.5719 I believe this entry is for the reaction is: MgOH+ + H+ -> Mg++ + H2O delG0f -626.8 0 -454.8 -228.57 (kJ/mol) And using these deltaG0formations (at 25oC; from Stumm and Morgan), I get a deltaG0reaction of -56.57 kJ/mol. Using this deltaG0reaction, I calculate a log K of 9.9094. I believe the entry of 11.7908 is the log K value at 25oC. Is there something I’ve miscalculated? Thanks Bill

Hi Brian Thanks a lot. I found some old reports from the US Bureau of Mines on the thermodynamics of formation of Li2Si2O5 and Li2SiO3 (Bureau of Mines report # RI 8187, 1976). They include a table of deltaH, deltaG and Log10K for a range of temperatures. These data lead me to two more questions for you. 1 - their formation reaction includes solids and gas to form the Li-silicate mineral. All basis species in GWB seem to be dissolved species [e.g., Li+ is the basis, not Li(s)]. So must I combine additional reactions to recast their formation reaction into a dissolution reaction for inclusion in GWB? 2 - their reported temperatures do not match the principal temperatures used in GWB. Can one assign different principle temperatures for computations associated with e.g. one specific mineral added to the thermo database? and then the default principle temperatures are used for everything else? Regards Bill

I am trying to model the solubility of glass dissolution products. One challenge is that glass is not a mineral and that secondary dissolution/re-precipitation products are amorphous gel-like substances. XRD from our experiments matches a phase reported (in the powder diffraction file) as Li2Si2O5*nH2O. A glass chemistry textbook I have includes some thermodynamic data for this phase (delH and S, both at 25C), however, I was wondering if anyone out there has tried to add this phase to their thermo.dat file and has some values for log K at the temps used in the GWB entries? Thanks Bill Burgos