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Basalt weathering


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HI everyone,

 

I am working on simulating basalt weathering. I wish to show with the help of GWB that:
1) Basalt weathers directly to kaolinite under slightly acidic conditions and flowing water
2) Basalt weathers to smectite under slightly acidic conditions and/or stagnant water condition
3) Smectite formed in turn again weathers to kaolinite under acidic flowing water conditions

All above are facts and I would just like to show these conditions using GWB simulations.

Following are the steps taken to do the same:

1) Inlet Pane: Rainwater composition

2) Reactant pane: Albite, Anorthite, K-feldspar, Diopside, Fayalite, Quartz voloume % specified as found in basalt. The rate constants, Specific surface area and nucleus density provided for all the above mentioned minerals as well as for Kaolinite and Smectite-low-Fe-Mg.

3) Initial pane: same as inlet

4) Domain pane: Linear with 1m x 1m x 1m volume of rock, discharge = 1m/year, 100 nodes

5) Medium pane: Porosity = 5%

 

Problems faced:

1) Should initial = inlet?

I am a bit confused by the "SOIL WEATHERING" example in Geochemical and Biogeochemical Reaction Modeling book by Dr. C. Bethke.

Shouldn't the initial condition be the rock composition and the inlet be the rainwater composition?

 

2) I am getting result only in case of Albite % = 80-90, rest all composition combinations are either not converging or there is excessive charge imbalance or decrease in porosity at "node 1"

 

3) Even if I am taking Anorthite or Diopside as 90 volume % and nothing else, I am not getting results.

 

 

I would be very grateful to you if you can guide me through solving my problem statement.

 

> time start = 0 day, end = 1 yr
> width = 1 m
> height = 1 m
> Nx = 100
> discharge = 1 m/yr
> porosity = .05
> dispersivity = 1 cm
> scope = initial
> H2O = 1 free kg
> HCO3- = .1 mg/l
> pH = 7
> Na+ = 2 mg/l
> Cl- = 3.8 mg/l
> balance on Cl-
> K+ = .3 mg/l
> Mg++ = .3 mg/l
> Ca++ = .1 mg/kg
> SO4-- = .6 mg/l
> O2(aq) = 7 mg/kg
> Al+++ = 1 ug/kg
> SiO2(aq) = 1 ug/kg
> Fe++ = 1 ug/kg
> scope = inlet
> H2O = 1 free kg
> HCO3- = .1 mg/l
> pH = 7
> Na+ = 2 mg/l
> Cl- = 3.8 mg/l
> balance on Cl-
> K+ = .3 mg/l
> Mg++ = .3 mg/l
> Ca++ = .1 mg/l
> SO4-- = .6 mg/l
> O2(aq) = 7 mg/kg
> Al+++ = 1 ug/kg
> SiO2(aq) = 1 ug/kg
> Fe++ = 1 ug/kg
> fix fugacity of CO2(g)
> kinetic K-feldspar rate_con = 3e-17 surface = 1000 nucleus = 4000
> kinetic Albite 25 volume% rate_con = 1e-16 surface = 1000
> kinetic Quartz 2 volume% rate_con = 4.2e-18 surface = 1000 nucleus = 4000
> kinetic Kaolinite rate_con = 1e-17 surface = 1e5 nucleus = 4000
> kinetic Gibbsite rate_con = 5e-17 surface = 4000 nucleus = 4000
> kinetic Anorthite 20 volume% rate_con = 3.16e-8 surface = 1000 nucleus = 4000
> kinetic Diopside 25 volume% rate_con = 4.36e-11 surface = 600 nucleus = 4000
> kinetic Fayalite 5 volume% rate_con = 1.58e-5 surface = 1000
> kinetic Smectite-low-Fe-Mg rate_con = 1.05e-15 surface = 6.1e5 nucleus = 4000
> precip = off

 

Thank you.

Basalt_Weathering.x1t

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