Water speciation fixing pH and [CO2(aq)]

[Jicé]

Hello all,

Does anybody know how to run a simulation given:
- a fixed pH
- a fixed dissolved Carbon Dioxide [CO2(aq)] concentration;

Currently, I'm:
- Calculating CO2 partial pressure (pCO2) depending on water temperature, expected [CO2(aq)], pH and m-Alkalinity;
- Running a EQUILIBRIUM_PHASES PhreeqC simulation using this pCO2, as well as an amount of 10mol [CO2(g)] initially present in the GasPhase;

My problem today is that:
- even if I got almost the same [CO2(aq)]: 0,549ppmCO2 simulated by PhreeqC starting from 0,555ppmCO2 expected;
- pH simulated by PhreeqC is 8,99, whereas expected pH is 9,39;

Any advice on this?

Thanks in advance,

[dlparkhurst]

If you want a fixed pH and fixed PCO2, then you can use EQUILIBRIUM_PHASES with Fix_pH and CO2(g). So I am not sure what else you are trying to do simultaneously. Perhaps you should attach a file.