Well,

It is supposed to take into account all the concentrations of major , secondary ions and trace elements and are introduced into phreeqc program, taking into account the program results of the saturation indices of each compound, to determine the sources of the elements required in your study. means define reactions achieved by the data base which generate them.

Sincerely

Thank you for your answer, it means that the reactions will be generated by the database based on the input solution.

Hi Shakthi,

I guess it is really up to you! You can define your own reactions for your particular system, or you can also use the ones available in the Phreeqc database. But please note that the reactions and the subsequent parameters in the Phreeqc database is based on a specific system studied by some investigator. So, the exact reactions and/or the relevant parameters might not be valid for your particular system. I guess you need to decide first what exactly (process) you want to model with the surface complexation, and then you can select appropiate reactions and so on.

Dear Muhammad Muniruzzaman,

Thank you for your response, I'm quite new to PHREEQC therefore I really value it. Actually what I would like to model with surface complexation is the adsorption of Hg, As and Fe heavy metals in a river assuming it as 1-D column along with advective and dispertive transport. Actually I read through your publication too and now I understand the complexity.

Hi,

first: You have to put your major ions concentrations. PHREEQC calculates the activity for each element and species, the activity coefficient is a function of the ionic strenght which its a function of all elements in your solution. If you don't put as an input all your elements concentrations (like Ca, Mg, Na, K, S, etc), then your activities are going to be WRONG, and then, all your subsequent modelation (precipitation, or sorption) will be wrong too.

Answering your question: Your code precipitates/dissolves (in EQUILIBRIUM_PHASES) Goethite, if you do not have Goethite defined in the database(default is PHREEQC.dat), then is not going to work. Lucky you, it is defined in the database :). You can't model something that is not on your database., The reaction for goethite is defined as :

Goethite

FeOOH + 3 H+ = Fe+3 + 2 H2O

-log_k -1.0

-delta_h -14.48 kcal

-Vm 20.84

Please check the database prior to make any simulation :).

For example, Arsenic, is not defined in the PHREEQC.dat database, so you can't use arsenic. Maybe you could use the WATEQ4F.dat database for your purpose.

And finally. Fe (2) and Fe(3) are sensitive to "pe", so make sure you are using your correct pe value in input, and that the resulting pe is close to your observed pe.

Hi Hi Shakthi,

Surely, modelling a geochemical system from a realistic basis is not easy!

By the way, Leonardo suggested above that it would be better idea to include the major ions as well. And also, As is not included in phreeqc.dat but in wateq4f.dat. On the other hand, Hg is not included in in phreeqc.dat either, but you can find it in minteq.dat. So, you need to compile those aqeuous reactions first. Afterwards, you can try with the database surface reactions as a very first trial (then again, I don't know if Hg surface reactions are in the database!). Next step would be to play around with the surface parameters and try to find literature values (if any) to reproduce your data (given that you have no information about the surface complexation parameters of your particular system).

Good luck!

Thank you all for the all the suggestions,

Yes I have used the minteq.dat for the simulations since had all the irons which was measured on field. I will follow your guidelines, thank you very much.

Shakthi