Beginners > PHREEQC basics

Converting from molality (mol/kgw) to mg/l for high solubility minerals

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dlparkhurst:
To do this calculation correctly, you will need to use pitzer.dat, phreeqc.dat, or Amm.dat. These databases have the molar volume information to calculate density accurately. The following gives the molality, mol/L, and mol/kgs concentrations for a solution saturated with gypsum at 25 C.

SOLUTION
END
USE solution 1
EQUILIBRIUM_PHASES 1
   Gypsum 0 10
USER_PRINT
10 PRINT "Density:   ", RHO
20 PRINT "SO4, mol/kgw (molality): ", TOT("S(6)")
30 PRINT "SO4, mol/L:              ", TOTMOL("S(6)") / SOLN_VOL
40 PRINT "SO4, mol/kgs:            ", (TOTMOL("S(6)") / SOLN_VOL) * RHO

Results:

Density:      9.9908e-01
SO4, mol/kgw (molality):    1.5085e-02
SO4, mol/L:                 1.5040e-02
SO4, mol/kgs:               1.5026e-02

Tom:
Great! Thanks David, that is a considerable improvement which will certainly help myself and hopefully others.


For clarification, am I right in thinking this BASIC line would give mg SO4/L ?

50 PRINT "SO4, mg/l:            ", (TOTMOL("S(6)") * 96.06) / SOLN_VOL


and then this line would give mg SO4/kgs ?

60 PRINT "SO4, mg/kgs:        ', ((TOTMOL("S(6)") * 96.06) / SOLN_VOL) * RHO

Thanks

dlparkhurst:
Yes. Note that TOT("S(6)") is the sum of all SO4-2 species (SO4-2, NaSO4-, CaSO4, etc), not just the bare ion SO4-2 (which would be MOL("SO4-2").

dlparkhurst:
Think you also need a factor of 1000 mg/g. 96 is g/mol, and you want mg.

Note you can use GFW("SO4") to calculate the gram formula weight of sulfate.

Tom:
Ahh yes, great spot, thanks.

I had copied it from the file where I was after simply g/l.

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