Moles of H2O with high precision when modeling evaporation to NaCl precip. start

[MichaelZ20]

Hi David,
How can I get moles of H2O with high precision when modeling evaporation to NaCl precipitation start?

DATABASE C:\phreeqc\database\pitzer.dat
SOLUTION_SPREAD
Number   Temp   Density   pH   Ca   Mg   Na   K   Cl   S(6)   Alkalinity
1   25   1.0   6.94   0.0995   0.0354   0.189   0.0101   0.228   0.0586   0.117        
END

USE SOLUTION 1

EQUILIBRIUM_PHASES 1
    Calcite    0    0
    Gypsum     0    0
    Halite     0    H2O  10
   
PRINT
    -high_precision true

USER_PRINT
10 PRINT "Water removal, mol    =   " ??? 
END

Thank you in advance for your reply!

[dlparkhurst]

Mass balance on water is a little tricky. Here I've calculated  (1) the difference in moles of water between the initial and final solution, (2) the amount of water removed by removing water to equilibrate with halite, (3) the water lost to gypsum, and (4) the difference, which I attribute to hydrolysis of HCO3, MgOH+, HSO4-, etc.

Code: [Select]

SOLUTION_SPREAD
Number Temp Density pH Ca Mg Na K Cl S(6) Alkalinity
1 25 1.0 6.94 0.0995 0.0354 0.189 0.0101 0.228 0.0586 0.117       
END
USE SOLUTION 1
EQUILIBRIUM_PHASES 1
    Calcite    0    0
    Gypsum     0    0
    Halite     0    H2O  10
PRINT
    -high_precision true
USER_PRINT
10 PRINT "Change in moles of water, mol     =   ", str_f$((GET(1) - TOT("water"))*1000/GFW("H2O"),20,12)
20 PRINT "Water removed by evaporation, mol =   ", str_f$(EQUI("Halite") - 10.,20,12)
30 PRINT "Water removed by gypsum, mol      =   ", str_f$(EQUI("Gypsum")*2,20,12)
40 diff = (GET(1) - TOT("water"))*1000/GFW("H2O") - (EQUI("Halite") - 10) - EQUI("Gypsum")*2
50 PRINT "Difference, hydrolysis, mol       =   ", str_f$(diff, 20, 12)
END


[MichaelZ20]

David, thank you for your help, but somewhere PUT is absent.

[dlparkhurst]

Sorry, missed the top two lines:

Code: [Select]

USER_PRINT
10 PUT(TOT("water"),1)


[MichaelZ20]

Thank you, David!