Re: Alkaline Solutions and CO2

["David L Parkhurst" <dlpark@xxxxxxxx>]

Here's a file that should help. It adds CO2 to your solution until calcite
is saturated. It also adds NaOH to maintain the pH at 10. If you add enough
CO2 to get close to 1 atmosphere pCO2 (as it looks like you intended from
your input file), you will have a very concentrated solution of NaHCO3 and
the program could fail to converge. . In this run, it takes about 25
micromoles of CO2 to get to calcite saturation, but you need to add 100
micromoles of NaOH and log(pCO2) is -7. It helps to add the oxygen to
define the redox condition more robustly.

David




SOLUTION 1 Nutrient Solution, pH 10, No CO2
temp 30
pH 10
pe 4
redox pe
units umol/kgw
density 1
B 0.16
Ca 700
Cl 256 charge
K 133
Mg 133
Na 0
N(-3) 47
N(5) 423
P 3
Zn 0.1
Cu 0.04
Fe 5
Mn 0.2
S(6) 500
C 0.00001
-water 1 # kg

EQUILIBRIUM_PHASES 1
# Fix pO2 at .1 atm
O2(g) -1
# Add CO2(g) until calcite saturation
Calcite  0.0  CO2(g) 10
# Add NaOH to pH 10
FIX_H+  -10. NaOH 10

PHASES
# Fake phase used to fix pH
FIX_H+
      H+ = H+
      logK 0

END
David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225