Leaching

[Sergio]

Hello everyone.
I would like to understand how can I use the PHREEQC to obtain results about leaching of a solid sample with the concentrations below (ppm):
Cd 0,005; Cr 0,007; and others...
How can I put the element if there is not in the datebase, for example Ag.
My goal is understand the interactions between water and that sample, inside the soil, after mixing, and if there will be changes of pH and pE. I need to know if the changes of pH and pE aftermath in some new ionic elements in these enviroment aqueous. If Cr+3 can be Cr+6 in some cases.
Ask me if someone need more information. Right?
Thanks a lot. I'm waiting for their response.

[dlparkhurst]

Most databases have NO3-, which is defined in SOLUTION_MASTER_SPECIES as N(5).

Ag is in wateq4f.dat, llnl.dat, minteq.dat, and minteq.v4.dat. You can use them for examples for ion-association aqueous models. Ag is also in sit.dat, the specific-ion interaction aqueous model.

If you are concerned with pH and pe, you probably need to look at the major element reactions (including iron). Reactions with these elements are most likely to control the chemistry of your setting. If you have water chemistry for water that has reacted with your rock, it is possible to use INVERSE_MODELING to try to figure out the major reactions.

Trace metals are going to be difficult to model with PHREEQC because they are unlikely to be derived from pure phases or form pure phases. Known stoichiometry is needed for INVERSE_MODELING and the stoichiometry of the reactive part of the source rock may be difficult to know for trace elements. Likewise sorption or incorporation as trace constituents in precipitates are likely to affect trace element concentrations. Although SURFACE and SOLID_SOLUTION can treat some of these processes, they may not be appropriate or you may not have the thermodynamic data (log Ks) that you need.

[Sergio]

Is possible to do study hydrogeochemistry with my sample in this software? I have Ag+, Cr+, Cl-, Ca+2.
What the dynamic interactions these elements of my sample and water. I know that I will have Ca(OH)2 for example. But I need to know if will appear another thing. I dont know yet.
Do you have any examples that I can use to obtains results something like that?
Do you have another examples how I can put Ag in my research?
Thanks again

[dlparkhurst]

I do not know if geochemical modeling is the right approach for your study. If you have chemical analyses, start by calculating saturation indices of minerals. That will give you an indication of whether minerals should dissolve or precipitate, or perhaps are reacting fast enough to maintain equilibrium.

[Sergio]

How can I obtain wateq4f.dat, minteq.dat and others. I need to use Ag and Cr. And they are not in database.

Send me more examples for my study. Please. I need to learn more and more about prhreeqc.

[dlparkhurst]

All databases are distributed with all versions of PHREEQC. If you are using the interactive version PhreeqcI, the Run screen allows you to select which database you want to use.

Start by reading SOLUTION and the examples in the manual, which is available from the Help button and also distributed with the distribution, generally in

C:\Program Files (x86)\USGS

[Sergio]

Ok. Thanks.
I will try  with your informations. If I have some problemas I will send my model and you tell me what happens...right??

[Sergio]

Hi.
I´ll try to do the model below but i cant declare the Ag and others. And I only declare the Cr+2. See the error message:


SOLUTION_MASTER_SPECIES
        Cr       Cr+2     0.0     51.996     51.996

SOLUTION_SPECIES
Cr+2 = Cr+2
log_k 0.0
   Cr(0)   Cr+2 alk gfw   

SOLUTION_MASTER_SPECIES
        Cr(2)    Cr+3     0.0     51.996

SOLUTION_SPECIES
Cr+3 = Cr+3
log_k  0.0


SOLUTION_SPECIES


Cr+2 + 2H2O = Cr(OH)2 + 2H+
                log_k          -11.089
                delta_h        18.153 kcal
 
Cr+3 + 3H2O = Cr(OH)3 + 3H+       
                log_k          -12.432
                delta_h        31.750 kcal

        Cr+2 + 3H2O = Cr(OH)3 + 3H+ + e-
                log_k          -5.157
                delta_h        10.752 kcal

Cr(OH)3 + H+ + e- = Cr(OH)2 + H2O
                log_k          -5.931
                delta_h        7.402 kcal


ERROR: Could not reduce equation to primary master species, Cr+3.
ERROR: Every primary master species for a redox element
   must also be a secondary master species.
   Cr+2 is the primary master species for element Cr.
   Another entry in SOLUTION_MASTER_SPECIES is needed.
   Define species Cr+2 as a secondary master species for a valence state.
   For example:
   Cr(0)   Cr+2 alk gfw
WARNING: Could not find element in database, Ag.
   Concentration is set to zero.
WARNING: Could not find element in database, CN.
   Concentration is set to zero.
WARNING: Could not find element in database, Hg.
   Concentration is set to zero.
WARNING: Could not find element in database, Se.
   Concentration is set to zero.
ERROR: Calculations terminating due to input errors.


What I made mistake? I wait for your response.
Thanks a lot.

[dlparkhurst]

I suggest first, do not define the elements and aqueous species. Use llnl.dat or minteq.v4.dat, which have definitions for Cr.

If you really need to define Cr yourself, then use these databases as examples.

[Sergio]

I define Cr.
But I am not too secure about my results. The software can resolve the situations some like:
One sample solid mixing water, acid or not, can dissolve some ions, depends on Kps, right? I will mix two solutions, the first only water and another solution with many elements. The software will give me all possible reactions when the water mixing with the aqueus ions? Including redox and pH?
Ca+2 transformin in Ca(OH)2 or Fe+2 turning Fe+3. Or, and other situation, Cr+3 reducing in Cr+2 or vice-versa. Or will I have to declare the reactions?

[dlparkhurst]

Too many questions. Try it and look carefully at the results.