Equilibrim - Isotopes (SO4 and H2O)

[fcgarcia]

Hi everyone,
I'm new in phreeqc and have a problem estimating mixing percentages between different types of waters in a mining environment.
The problem is that I need to estimate % of different water, but I don't have enough info about the extreme members. Until now, I already know with more certainty that I have natural water (I know SO4 concentration, SO4 isotopes, and H2O isotopes) and pre and postprocess water (SO4 concentration, SO4 isotopes, and H2O isotopes), but I don't know the water from tailings, and there is no way to have a sample. But, what I do have and know is the isotopic composition of SO4 within the tailings, and the concentration and isotope composition (SO4 and H2O) of process water that is used in the mine.
So, I was wondering if it is possible to use pheeqc to help with this problem and want to know what you think. Can I use equilibrium phases for my process water (input SO4 isotopes and H2O isotopes) and my SO4 tailing isotopes? Is it possible to do this on phreeqc ? Do you see a problem?
Thank you! Feedback will be welcome!

[dlparkhurst]

I'm not sure what you are trying to do. Are you trying to use INVERSE_MODELING to estimate the composition of a partially known solution, or are you trying to use forward modeling to estimate the composition of a tailings water?

Give a little more information on the actual water compositions and an attempt at the model you are proposing.

[dlparkhurst]

Maybe you just want to set up mole balance equations with the data that you have. It will be a little messy with four balances--34S, D, 18O, and sulfate, but possible, say in Excel. Perhaps just setting up the equations will give you some insight.