SOLUTION 1#temp 220#pressure 210pH 6.8units mg/Ldensity 1 calcCa 1.19Cl 101#F 21Fe 0.0025K 165Mg 0.5#N(-3) 8.2Na 1147S(6) 572Si 469 as SiO2Alkalinity 2343 as HCO3ENDREACTION_TEMPERATURE220USE solution 1EQUILIBRIUM_PHASESMtg(g) 2.3 10GAS_PHASE 1-fixed_volume-pressure 210-volume 1e-10CO2(g) 0Mtg(g) 0END

Dear David, Thank you very much for your suggestion. I tried to use your suggested code to Phreeqc (for Windows) but which ever database I would use, I was getting an error. Actually I was gettingERROR: Gas not found in PHASES data base, Mtg(g).ERROR: Phase not found in data base, Mtg(g).ERROR: Calculations terminating due to input errors.I am a bit confused why Mtg is not recognised. I tried to use Phreeqc Interactive, although I could add Mtg in the equilibrium and gas phase; however, in the gas phase I had to add an initial temperature (I used 220oC) and in the initial solution I could not define density 1 calc in the initial solution and also I had to add a pe. I used pitzer.dat.When I tried to run this, I got a Warning: Numerical method failed. [SOLUTION 1 temp 220 pH 6.8 pe 1.8 redox pe units mg/l density 1 Ca 1.19 Cl 101 F 21 Fe 0.0025 K 165 Mg 0.5 N(-3) 8.2 Na 1147 S(6) 572 Si 469 as SiO2 Alkalinity 2343 as HCO3 -water 1 # kgREACTION_TEMPERATURE 1 220GAS_PHASE 1 -fixed_volume -pressure 210 -volume 1e-010 -temperature 220 CO2(g) 0 Mtg(g) 0EQUILIBRIUM_PHASES 1 Mtg(g) 2.3 10]

SOLUTION density 1 calc