introducing new compounds in the database

[danaluminita]

Hi,

 

I am trying to make an Eh-pH diagram for Sb-S-H2O but my diagram is not similar with the ones from the literature. I'm using the thermo minteq data base in which I have introduced the H2 ion. My diagram is different from the one in the literature due to the fact that the database doesn't have the SbS2- compound. This compound is not included in the databases of the program. How can I introduce these new compound in the database?

 

Regards,

Dana

[Brian Farrell]

Hi Dana,

 

I don't know much specifically about antimony, but I found this entry for Sb2S4-- in thermo_minteq.dat:

 

Sb2S4--

charge= -2.0 ion size= 0.0 A b= 0.0000 mole wt.= 371.7560 g

4 species in reaction

2.000 H+ 2.000 Sb(OH)3 4.000 HS-

-6.000 H2O

-54.5480 -51.8554 -49.3886 -46.6884

-44.2350 -41.9961 -39.9448 -38.0583

* logK= -49.388600 deltaH= 321.780100 kJ

 

It has the same empirical formula as SbS2-, but if it is indeed a different species you would want to add a new entry for SbS2-. Luckily, you can view and modify thermo datasets in text editors like Notepad. You'll need to find a reaction for SbS2- in the literature, along with an equilibrium constant (log K) for that reaction. You may need to rebalance that reaction (and recalculate the log K) in terms of the Basis and redox species in the thermo dataset. The redox species are just Basis species in different oxidation states. The entry for Sb2S4-- shown above, for example, has been written in terms of the Redox species Sb(OH)3 and HS-, rather than the Basis species Sb(OH)6- and SO4--.

 

The information below the lines "4 species in reaction" actually represents a chemical reaction. Species with negative coefficients appear on the left side of the reaction with the entry of interest, while positive coefficients indicate species appearing on the right hand side. The reaction can be read as follows: Sb2S4-- + 6 H2O = 2 H+ + S Sb(OH)3 + 4 HS-. The block of 8 numbers below this section represents the equilibrium constant at each of the principal temperatures of the thermo dataset (0 to 100 C in thermo_minteq.dat).

 

Please refer to the Thermo datasets Appendix to the GWB Reference Manual for more information on formatting datasets. 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC