KINETICS quartz units

[geo_afonso]

I'm doing some rock simulations with a brine of 55.6 g/l salinity with supercritical CO2.
When I put quartz in the KINETICS block with a value in parms (1) of 0.733 in m2/mol as suggested by the database (phreeqc.dat), Silicon has a very low dissolution rate which is not compatible with the experimental results I have.
When I put the value in cm2/mol, i.e. 7330, the Silicon value increases, which is more compatible with the experimental results.
Do anyone know if the parms (1) value for quartz should be in cm2/mol or m2/mol?
Thanks in advance

[dlparkhurst]

phreeqc.dat does say m^2/mol.

You can try other rate expressions. You can use phreeqc_rates.dat, where quartz would be defined as follows for a Palandri and Kharaka rate according to the database notes:

Code: [Select]

RATES
Quartz_PK # Palandri and Kharaka, 2004
-start
 5  REM PARMS: 1 affinity, 2 m^2/mol, 3 roughness, 4 exponent
 10 if parm(1) = 1 then affinity = 1 else affinity = 1 - SR("Quartz") : if affinity < parm(1) then SAVE 0 : END
 20 rate = RATE_PK("Quartz")
 30 IF M > 0 THEN area = M * parm(2) * parm(3) * (M/M0)^parm(4) ELSE area = 0
 40 SAVE area * rate * affinity * TIME
-end
Or as follows for the Hermanska and others rate:

Code: [Select]

RATES
Quartz_Hermanska  2022
-start
 5  REM PARMS: 1 affinity, 2 m^2/mol, 3 roughness, 4 exponent
 10 if parm(1) = 1 then affinity = 1 else affinity = 1 - SR("Quartz") : if affinity < parm(1) then SAVE 0 : END
 20 rate = RATE_HERMANSKA("Quartz")
 30 IF M > 0 THEN area = M * parm(2) * parm(3) * (M/M0)^parm(4) ELSE area = 0
 40 SAVE area * rate * affinity * TIME
-end

You can also use Kinec_v3.dat, which I think should also give the Hermanska and others rate. Here is their definition:

Code: [Select]

Quartz#SiO2; M 60.08 g/mol
-start
1 name$ = "Quartz"
2 if (PARM(1) = 0) then  goto 3 else goto 5
3 if PARM(3) = 0 then S = PARM(2) * m * GFW(PHASE_FORMULA(name$)) else S = m0 * ((m/m0)^(2/3)) * GFW(PHASE_FORMULA(name$)) * PARM(2)
4 GOTO 100
5 S = PARM(2)*TOT("water")
##----------------- Dissolution only or precipitation only option---------------------##
100  if (PARM(4) = 0) then  goto 1000 else goto 110
110 if (PARM(4) = 1) Then GoTo 150 else goto 200 #
150 if (SR (name$) < 1) Then GoTo 5000 else goto 1000# warning no dissolution reaction
200 if (SR (name$) > 1) Then GoTo 5000 else goto 1000 # warning no precipitation reaction
##------------------Kinetic calculation---------------------##
#Parameters
1000 Aa = 4.03e-4#mol/m2/s
1001 Ab = 0.105#mol/m2/s
1002 na = 0.309
1003 nb = -0.41
1004 Ea = 45600
1005 Eb = 80000 
1006 R =  8.314 #J.deg-1.mol-1
1007 ACTI = act("H+")
1009 Sig = 1
#rate equations
2002 rplusa = Aa* (exp(-Ea/ (R * Tk)))*(ACTI^na)* S
2003 rplusb = Ab* (exp(-Eb/ (R * Tk)))*(ACTI^nb)* S
2009 rplus = rplusa + rplusb
3000 rate = rplus * (1 - (SR("Quartz")^(1/Sig)))
4000 moles = rate * time
5000 save moles
-end

with the following notes:

Code: [Select]

#Parameters:
#Four parameters are necessary when using rates from Kenec.dat:
# - The first parameter specifies if the specific surface area is entered as m2 per g of rock (0) or m2 per kg of water (1)
# - The second parameter specifies the specific surface area of the mineral (in m2/g or m2/kgw depending on the choice of the first parameter)
#  - The third parameters define how the surface area changes during dissolution and has three possible values. This option is only available when the first parameter is 0. If the first parameter is 1, the surface area is always constant.
#   0: The surface area changes linearly with the moles of the mineral present
#   1: The surface area changes according to the geometry of dissolving cubes or spheres
#- The fourth  parameter specifies the dissolution and precipitation option
# 0: allow dissolution and precipitation
# 1: allow precipitation only
# 2: allow dissolution only