Conceptual Models > Kinetics and rate controlling factors
Kinetics of Mineral precipitation combined with Brine water evaporation
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Jovel:
Hello Everyone,
I am trying to stimulate the kinetic precipitation of Calcite and Fe_tri(OH)3(a) from evaporating brine water in pitzer database.
Title Kinetics Modelling
SOLUTION_MASTER_SPECIES
O(0) O2 0.0 16.00
N NO3- 0.0 14.0067 14.0067
N(+3) NO2- 0.0 14.0067
N(+5) NO3- 0.0 14.0067
N(0) N2 0.0 14.0067
Fe_di Fe_di+2 0.0 Fe_di 55.847
Fe_tri Fe_tri+3 0.0 Fe_tri 55.847
SOLUTION_SPECIES
Fe_di+2 = Fe_di+2
log_k 0.0
Fe_di+2 + H2O = Fe_diOH+ + H+
log_k -9.5
delta_h 13.20 kcal
Fe_tri+3 = Fe_tri+3
log_k 0.0
Fe_tri+3 + H2O = Fe_triOH+2 + H+
log_k -2.19
delta_h 10.4 kcal
Fe_tri+3 + 2 H2O = Fe_tri(OH)2+ + 2 H+
log_k -5.67
delta_h 17.1 kcal
Fe_tri+3 + 3 H2O = Fe_tri(OH)3 + 3 H+
log_k -12.56
delta_h 24.8 kcal
PHASES
Fe_tri(OH)3(a)
Fe_tri(OH)3 + 3 H+ = Fe_tri+3 + 3 H2O
log_k 4.891
Goethite
Fe_triOOH + 3 H+ = Fe_tri+3 + 2 H2O
log_k -1.0
CO2(g)
CO2 = CO2
-log_k -1.468
-delta_h -4.776 kcal
-analytic 10.5624 -2.3547e-2 -3972.8 0 5.8746e5 1.9194e-5
-T_c 304.2 # critical T, K
-P_c 72.86 # critical P, atm
-Omega 0.225 # acentric factor
O2(g)
O2 = O2
-log_k -2.8983
-analytic -7.5001 7.8981e-3 0.0 0.0 2.0027e5
-T_c 154.6; -P_c 49.80; -Omega 0.021
N2(g)
N2 = N2
-log_k -3.1864
-analytic -58.453 1.818e-3 3199 17.909 -27460
-T_c 126.2; -P_c 33.50; -Omega 0.039
Solution 1
temp 26.3
pH 6.13
pe 1.01
unit mg/L
density 1.023
Li 24.5
Na 33600
K 1910
Mg 423
Ca 2850
Sr 61.2
F 0.22
Cl 57800 #Charge
Br 25
N(5) 12 as NH4+
S(6) 2720 as SO4-2
Al 0.47
Mn 2.7
Fe_di 29
O(0) 0.2
water 1.0 #1 kg of water
C(4) 1130 as CO2
EQUILIBRIUM_PHASES 1
CO2(g) -3.5 #equilibrium with atmosphere
O2(g) -0.68
Gypsum 0 0
KINETICS 1
Fe_di_ox
-formula Fe_di -1.0 Fe_tri 1.0
Fe_tri(OH)3(a)
-formula Fe_tri(OH)3(a)
-m 1 # Fe(OH)3(a)-Gehalt zu Beginn der Modellierung
-m0 1 # urspr?nglicher Fe_tri(OH)3(a), mol/L
-parms 22.6 0.162 # A0 in m2, V in dm3 (=L)
-time 86400 seconds in 50 steps # 86.400s in 60s Abschnitten ?
Calcite
-tol 1e-8
-m0 0.077#3.e-3
-m 0.077#3.e-3
-PARMS 50 0.6
RATES
Fe_di_ox
-start
10 Fe_di = TOT("Fe_di")
20 if (Fe_di <= 0) then goto 200
30 p_o2 = SR("O2(g)")
40 moles = (2.91e-9 + 1.33e12 * (ACT("OH-"))^2 * p_o2) * Fe_di * TIME
50 moles = 10^12 * (ACT("OH-"))^2 * (mNO3 + mo2) * Fe_di * TIME
200 SAVE moles
-end
Fe_tri(OH)3(a)
-start
10 A0 = parm(1)
20 V = parm(2)
30 rate = 10^-14 * (1 - SR("Fe_tri(OH)3(a)")) * A0/V * (m/m0)^0.67
40 moles = rate * time
50 SAVE moles
-end
Calcite
-start
1 rem parm(1) = A/V, 1/dm 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 / (273.16 + tc) )
40 k2 = 10^(2.84 - 2177.0 / (273.16 + tc) )
50 if tc <= 25 then k3 = 10^(-5.86 - 317.0 / (273.16 + tc) )
60 if tc > 25 then k3 = 10^(-1.1 - 1737.0 / (273.16 + tc) )
70 t = 1
80 if m0 > 0 then t = m/m0
90 if t = 0 then t = 1
100 moles = parm(1) * 0.1 * (t)^parm(2)
110 moles = moles * (k1 * act("H+") + k2 * act("CO2") + k3 * act("H2O"))
120 moles = moles * (1 - 10^(2/3*si_cc))
130 moles = moles * time
140 if (moles > m) then moles = m
150 if (moles >= 0) then goto 200
160 temp = tot("Ca")
170 mc = tot("C(4)")
180 if mc < temp then temp = mc
190 if -moles > temp then moles = -temp
200 save moles
-end
REACTION 1
H2O -1
28 moles in 50 steps
USER_GRAPH 1
-headings Time SI_Fe_tri(OH)3(a) pH
-axis_titles "Time, hours" "SI" "pH"
-initial_solutions false
-connect_simulations true
-plot_concentration_vs time
-start
5 GRAPH_X TOTAL_TIME/3600
10 GRAPH_Y SI("Fe_tri(OH)3(a)")
20 GRAPH_SY -LA("H+")
-end
USER_GRAPH 2
-headings Time SI_Calcite pH
-axis_titles "Time, hours" "SI" "pH"
-initial_solutions false
-connect_simulations true
-plot_concentration_vs time
-start
5 GRAPH_X TOTAL_TIME/3600
10 GRAPH_Y SI("Calcite")
20 GRAPH_SY -LA("H+")
-end
END
I have the following questions:
1) With pitzer database the SI of O2 is not similar to what is stimulated by atmospheric conditions. Is it possible to stimulate atmospheric conditions as the brine is in contact with atmosphere?
2) The SI of Fe_tri(OH)3(a) based on EQ_P is oversaturated and precipitates initially, However. Kinetic modelling of Fe_tri(OH)3(a) is different than expected. Is there a way to modify the kinetics of precipitation of Fe_tri(OH)3(a).
3) Will the water evaporation step significantly affect mineral precipitation other than pH
Any help and suggestions will be much appreciated.
Thank you
Jovel
dlparkhurst:
(1) You should not use pitzer.dat for this calculation. There are no interactions coefficients for Fe(2) or Fe(3), and so, the activity coefficients will not be meaningful. In general, there are no redox reactions in pitzer.dat. Dissolved oxygen (Oxg) is defined only as an unreactive species.
(2) "Kinetic modelling of Fe_tri(OH)3(a) is different than expected." Really? How am I to know what you expected? My guess is that because there are no redox reactions, you get strange results. Kinetics is very flexible, and I am sure could be adapted to your needs, whatever they are.
(3) Yes, if you remove half the water, you will precipitate more calcite and Fe(OH)3.
Jovel:
Thank you dlparkhurst for your response. I was trying to consider the Pitzer database as the ionic strength is much higher due to the evaporation process but I will consider the phreeqc database for my calculations.
Thanks again.
Jovel
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