PHREEQC is a computer program written in the C++ and C programming languages that is designed to perform a wide variety of aqueous geochemical calculations.
I used PHREEQC to perform geochemical calculation on the mineral phases occurring in a lake but would like to know how to validate the results.
To validate your result at least you have to go for the geochemistry of the Aquifer system for verification.
Since it is a lake water chemistry problem, you would need to collect samples of lake sediments.
This is a tricky problem.
1) Are you sure of the correctness of the water analyzes? Is the solution electrically neutral?
2) Is the correct ionic activity model chosen for the real ionic strength of the solution?
Look, for example, in (Broder J. Merkel · Britta Planer-Friedrich. Groundwater Geochemistry. A Practical Guide to Modeling of Natural and Contaminated Aquatic Systems).
Perhaps you need to change the database, for example, from freexi to pitzer.
3) Have any existing and possible minerals introduced into the system?
4) If you are sure that the solution is in equilibrium with some minerals, then the model solution should also be in equilibrium with them (no dissolution, no precipitation). The temperature at the place of interaction with minerals differs from the temperature of the laboratory; the analysis must be calibrated about the temperature of the lake.
5) If the system is open in air, then it is necessary to select the partial pressure of CO2 first. The criterion is balance with existing minerals.
6) If the system is closed to air, then it must be remembered that НСО3- is usually analyzed, but there is also H2CO3 and CO3--.
They must be found, for example, by calculation; or selection of Р(СО2) with control according to the correspondence of pH.
Only after these operations have been completed, it is possible to simulate hydrogeochemical processes in the lake.
Good luck
That is a very good question and I was doing the same search, then I came along with an article written by McCleskey et al, 2012. "A new method of calculating electrical conductivity with applications to natural waters". The idea is as follows: if you have measurements from Electric conductivity on your waters and you calculate the electric conductivity and charge balance with Phreeqc, they have calculated corrections for each element regarding ionic strength and Temperature. They utilise a correction for ionic molal conductivity with Lattey's equation that accounts for variations on a range of 0-95°C and up to 1 mol/kg in ionic strength. The code runs smoothly, but bear in mind that the calculations depend on your data but also on the accuracy of the database you use.
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