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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