I'm trying to model the kinetics of replacement of calaverite (AuTe2) by gold (Au), in order to fit experimental data.
A simple model with a simple kinetics low for calaverite works rather well if I suppress Au(OH)(aq) from the run. If I use Au(OH)(aq), then the model predicts that my experimental solution is always undersaturated with respect to native Au, and hence calaverite dissolves, but no gold is formed. There is little justification for suppressing Au(OH)(aq) - it is well characterized at 300C and Steffanson and Seward (2003) suggest that the properties are good to ~200C (I'm working at 220C).
It seems that my problem could be solved if I could 1) force gold to precipitate, even in an undersaturated solution (Q/K = 1e-5), and 2) prevent the formed Au to dissolve once it has formed.
I've tried a negative reaction rate for Au (negative is precipitation, right?), in conjuction with the nucleus keyword, but had no luck - always zero mole of Au in the system.
I'm using react v. 7.0.3, and the script with kinetic laws for both Au and Calaverite is below. Let me know if you want the database and conf file to have a play.
Kinetic run: forcing a mineral to precipitate, even if it is undersaturated
in Kinetics and microbes
Posted
Dear group,
I'm trying to model the kinetics of replacement of calaverite (AuTe2) by gold (Au), in order to fit experimental data.
A simple model with a simple kinetics low for calaverite works rather well if I suppress Au(OH)(aq) from the run. If I use Au(OH)(aq), then the model predicts that my experimental solution is always undersaturated with respect to native Au, and hence calaverite dissolves, but no gold is formed. There is little justification for suppressing Au(OH)(aq) - it is well characterized at 300C and Steffanson and Seward (2003) suggest that the properties are good to ~200C (I'm working at 220C).
It seems that my problem could be solved if I could 1) force gold to precipitate, even in an undersaturated solution (Q/K = 1e-5), and 2) prevent the formed Au to dissolve once it has formed.
I've tried a negative reaction rate for Au (negative is precipitation, right?), in conjuction with the nucleus keyword, but had no luck - always zero mole of Au in the system.
Two example runs are visible at
http://gallery.me.com/minmetsol/100108.
I'm using react v. 7.0.3, and the script with kinetic laws for both Au and Calaverite is below. Let me know if you want the database and conf file to have a play.
Thanks for your help,
JOEL
React> show
Reaction runs from 0 years to 2.5 days
Temperature is 220 C
Thermo dataset: ..\thermo_MMS_11May18.dat
Working directory: z:\gwb_work\tellurium
Options: Debye-Huckel
Basis is:
H2O .015 free kg
Na+ .1054 molal
Cl- .01 molal
H2TeO3(aq) 1e-8 molal
O2(aq) 8.45e-5 mol
Au+ 1e-8 molal
HPO4-- .1998 molal
H+ charge balance
Reactants:
10 mg of Calaverite by kinetic rate law
Rate constant = 1.8e-9 mol/cm2 sec
Specific surface area = 51.06 cm2/g
React 0 mol of O2(aq)
Au by kinetic rate law
Rate constant = -3e-9 mol/cm2 sec
Specific surface area = 100 cm2/g
Nucleus density = 200 cm2/cm3
Critical saturation index = 1e-8
Other "show" options: type "show show"