Database selection and creation

[sumana]

Hello,

I was introduced to the capabilities of Phreeqc last week and I would be using it for my masters thesis purpose.
I am a Geotechnical Engineering student and have high school level Chemistry knowledge.

I am trying to model ureolytic calcite precipitation and as an effect decrease in porosity of porous media.

I am having very tough time in figuring out how to introduce urea as an input and which database file to use.

Should I create a solution master species named urea with its molecular weight? In the solution_species which equations should I put and how to know which combination can occur? My input solution only contains urea and calcium Chloride. How to calculate log k and delta h values? I am really having very difficult time in creating (or understanding) the database. Does the solution_species database indicate all probable reactions that can take place with my created species as a reactant?

Do the Basic key words get_por and change_por take into account change in porosity due to calcite precipitation?

Any help regarding database is highly solicited and appreciated. Kindly let me know if my questions are not clear.

Any reference to any documents is also highly appreciated. I have my presentation on 2nd Dec.

Thank you very much in advance.

Sumana

[dlparkhurst]

You can look at the minteq.v4.dat database for the definition of a number of organic ligands, although not urea. You would need the protonation/deprotonation reactions for urea--balanced chemical reactions and log Ks. You should also consider the binding of urea with calcium, again balance reaction and log K. You will have to go to the literature to try to find the log Ks, delta H also if temperature effects are important. You will need an entry in SOLUTION_MASTER_SPECIES to define the "element" Urea. You will need species definitions in SOLUTION_SPECIES for all Urea species found in solution. The log Ks allow equilibrium to be calculated among all of the aqueous species.

You will have to read the manual and  look at the databases to see how to define the species. Porosity is used only in TRANSPORT calculations. You have to define the porosity change yourself with get/set porosity. I suggest you stay with simpler reaction calculations with your limited time.l