Can be the non water H and O related to the pH?

[Pak]

I was just wondering if somebody knows if there is a way to relate the nonwater H and O given by iPhreeqc or PhreeqcRm with the pH.

Thank you

[dlparkhurst]

There is no simple relationship between non-water H and O and pH, at least in any system other than pure water. Note that non-water H and O includes species like SO4-2 and HCO3-.

The totals of every element, including H and O, plus the charge imbalance is sufficient to calculate the pH, pe, and distribution of species, but that requires solving the nonlinear set of mole balance and mass action equations.

[Jeonghwan Hwang]

I had a question about non-water O at reply. "Note that non-water H and O includes species like SO4-2 and HCO3-"

If the system had gypsum, can the change of non-water O significantly affects to dissolution of gypsum? Assume that the non-water O was changed by some reasons.
I confused because I think that the non-water O, non-water H, and charge imbalance are coupling parameters and should not affect to modeling results, significantly.
But my modeling results showed that the change of non-water O affected to gypsum dissolution...
In my model, the change of non-water O is due to the diffusion between 2 different material.
Material 1 with gypsum has a higher concentration of non-water O, and material 2 without gypsum has a lower concentration of non-water O. Over time, the concentration of non-water O decreases at the boundary of material 1 and dissolution of the gypsum occurs.

If my model showed that results, can I say that it is geochemically right?

Thank you

[dlparkhurst]

Assuming charge balance, adding only O from some source is equivalent to adding O2, or generating a more oxidizing environment. Removing O makes a more reducing environment, which could produce sulfate reduction and dissolution of gypsum.

Looking at the concentrations of non-water H and O may not be the best way to analyze your system. If gypsum dissolves or precipitates it is because of changes in the activities of Ca+2, SO4-2, and H2O. I would look at why those quantities change.