Processes > Reactive transport modelling
Transport with kinetic of calcite precipitation
(1/1)
WJJ:
Dear all,
I am currently trying to investigate calcite precipitation within a column. The problem consists of three stages: 1. dissolution of aragonite in the H2O-CO2-CaCO3 system, which is referred to as 'aragonite dissolution' in the script below; 2. aeration to increase the saturation index of calcite, which is referred to as 'aeration (decreasing CO2)'; 3. then the output solution is defined as solution 0 that will transport to the domain. In summary, the solution with SI_calcite of 0.4 transports to the domain, and calcite is expected to precipitate as the reactive solution transports through the cell. However, it seems that my code does not work well. Could you give me some suggestions or recommendations? Thank you.
--- Code: ---RATES
Calcite
-start
1 rem M = current number of moles of calcite
2 rem M0 = number of moles of calcite initially present
3 rem PARM(1) = A/V, cm^2/L
4 rem PARM(2) = exponent for M/M0
10 si_cc = SI("Calcite")
20 if (M <= 0 and si_cc < 0) then goto 200
30 k1 = 10^(0.198 - 444.0 / TK )
40 k2 = 10^(2.84 - 2177.0 / TK)
50 if TC <= 25 then k3 = 10^(-5.86 - 317.0 / TK )
60 if TC > 25 then k3 = 10^(-1.1 - 1737.0 / TK )
70 t = 1
80 if M0 > 0 then t = M/M0
90 if t = 0 then t = 1
100 area = PARM(1) * (t)^PARM(2)
110 rf = k1*ACT("H+")+k2*ACT("CO2")+k3*ACT("H2O")
120 rem 1e-3 converts mmol to mol
130 rate = area * 1e-3 * rf * (1 - 10^(2/3*si_cc))
140 moles = rate * TIME
200 SAVE moles
-end
END
# aragonite dissolution
SOLUTION 0
temp 25
pH 7
pe 4
redox pe
units mmol/kgw
density 1
-water 1 # kg
EQUILIBRIUM_PHASES 1
Aragonite 0 10
CO2(g) -0.1 10
Calcite 0 0
SAVE solution 0
End
# Aeration (decreasing CO2)
USE solution 0
EQUILIBRIUM_PHASES 2
Calcite 0.4 0
REACTION 1
CO2(g) 1
-30.5 millimoles in 1 steps
SAVE solution 0
END
solution 1-20
temp 25
pH 7
pe 4
redox pe
units mmol/kgw
density 1
-water 1 # kg
SAVE solution 1-20
END
KINETICS 1-20
Calcite
-m0 0
-parms 5.0 1
-tol 1.e-8
END
TRANSPORT
-cells 20
-lengths 0.002
-shifts 200
-time_step 36 secs
-flow_direction forward
-boundary_conditions constant constant
-diffusion_coefficient 1.0e-9
-dispersivities 0
-print_frequency 5
-punch_frequency 5
USER_GRAPH 1
-headings Dist pH
-axis_titles "Distance" "Ca+2"
-start
10 GRAPH_X DIST
20 GRAPH_Y m("Ca+2")
-end
END
--- End code ---
dlparkhurst:
1. If you include Calcite in equilibrium phases, then all of the aragonite dissolves and reprecipitates as calcite.
2. I suggest you set the CO2(g) partial pressure to -3.4 in equilibrium phases, rather than REACTION.
3. The definition of EQUILIBRIUM_PHASES 1 will be used in cell 1 in the TRANSPORT calculation. And, you probably don't want a constant boundary condition at the outlet.
WJJ:
Thank you for your kind help! I will try as you suggested.
dlparkhurst:
And m("Ca+2") is not the correct Basic function.
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