> I am trying to model a pyrite system with cyanide so that thiocyanate forms. MINTEQ is the only database with cyanide species however there is no thiocyanate. llnl.dat has a limited amount of data on cyanide and thiocyanide. How does one enter a new species into the database? or is there an updated version of the database? (I am using PHREEQC 2.4.2) You enter new "elements" in the database with the SOLUTION_MASTER_SPECIES data block. New aqueous species are defined with SOLUTION_SPECIES. > I would appreciate your feedback on this matter. I think it may be a bit tricky to model cyanide reactions. I suspect that they are metastable and are only formed kinetically. The approach in minteq.dat and llnl.dat are different. In llnl.dat, cyanide is composed of C and N, and the cyanide species will be in equilibrium with all other C and N aqueous species. Thus, I would guess, if you enter cyanide in the initial solution, it will exist in the initial solution calculation, but will decompose to equilibrium products when you run any kind of reaction (equilibrate with a mineral, add a reactant (REACTION), etc) because reaction calculations always impose redox equilibrium. Minteq.dat defines an "element" named Cyanide. This element does not know it is composed of C and N, and there is no equilibrium between Cyanide and other C and N species. Thus, it will exist at the same total concentration unless you add or remove some of it in the reaction calculations. The speciation may vary as pH and ligand concentrations vary through reactions. I am guessing that you will need to use the minteq.dat approach if you want to keep any cyanide in solution. I don't know if you can model thiocyanide as an equilibrium reaction between cyanide and HS-, or you need a separate element for thiocyanide as well. If separate, you would probably define reactions between them kinetically with KINETICS and RATES. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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