PhreeqcUsers Discussion Forum
Beginners => PHREEQC basics => Topic started by: frenzy_geochem on April 02, 2020, 01:00:57 PM

Hii all,
Today, I got stuck on a little problem. I want to try and simulate how H2S(g) created from Solution 1 reacts with Solution 2. I cannot put 'USE solution 1' as I want to keep the solutions seperated. It is only the H2S(g) I want to add to Solution 2. When that has happened, I want to heat solution 2 (but I don't think that is a problem). Any ideas?
PHASES
H2S(g)
H2S = + 1.0000 H+ + 1.0000 HS
log_k 7.9759
delta_h 1.08 kcal
Fix_pH
H+ = H+
log_k 0
SOLUTION 1
water 0.0155
temp 25
pH 0.15
Na 1.29
S(2) 0.645
S(6) 0.71
END
EQUILIBRIUM_PHASES
Fix_pH 7 NaOH 10
SOLUTION 2
water 0.04
temp 25
pH 2
Fe(+3) 0.3
Cl 0.9
END
REACTION_TEMPERATURE 1
25.0 85.0 in 12 steps
USE Solution 2
USE Reaction_temperature 1
END

You haven't created any H2S(g) with solution 1. You need to use either EQUILIBRIUM_PHASES or GAS_PHASE to partition H2S(g) out of solution into a gas phase. If the gas evolves to a known partial pressure, you could use EQUILIBRIUM_PHASES. If the gas evolves into a fixed volume (or fixed pressure), you could use GAS_PHASE.
Here is one experiment where 1 L (kg water) evolves H2S(g) into 1 liter of head space.
SOLUTION 1
water 0.0155
temp 25
pH 0.15
Na 1.29
S(2) 0.645
S(6) 0.71
END
USE solution 1
GAS_PHASE 1
fixed_volume
pressure 1
volume 1
temperature 25
H2S(g) 0
SAVE gas_phase 1
END
SOLUTION 2
USE gas_phase 1
END