Rate equations in database and finding relevant equations of the reactions

[Chatura]

Hi all,

I am a new PHREEQC  user in the field of engineering. Thank you for this forum. I have two questions attached here that faced during my simulation.

1.
I have simulated some mineral brine interactions with kinetic parameters in llnl.dat database.
I have found that their rate equations are different from the literature that I used.
So is there any reference material to know about the rate equations (terms and parameters) used in the llnl database and that will help me to select what suits me.
I hereby attach the llnl rate equations and the equations that I used. The output is vary according to the rate.

2.
Since I am not fully aware of the chemistry part, I want to know the equations that my simulation used when getting it's output. That means when I get the SI what are the reactants that Quartz, Feldspar and other minerals react with the. Is there a way to check the relevant equation. Because the database has all the equations which are relevant and irrelevant.

Thank you.

Code: [Select]

#In llnl

Albite
 -start
1   REM Sverdrup and Warfvinge, 1995, mol m^-2 s^-1
2   REM PARM(1) = Specific area of Albite m^2/mol Albite
3   REM PARM(2) = Adjusts lab rate to field rate
4   REM temp corr: from A&P, p. 162. E (kJ/mol) / R / 2.303 = H in H*(1/T-1/281)
5   REM Albite parameters
10  DATA 11.5, 0.5, 4e-6, 0.4, 500e-6, 0.2, 13.7, 0.14, 0.15, 11.8, 0.3
20  RESTORE 10
30  READ pK_H, n_H, lim_Al, x_Al, lim_BC, x_BC, pK_H2O, z_Al, z_BC, pK_OH, o_OH
40  DATA 3500, 2000, 2500, 2000
50  RESTORE 40
60  READ e_H, e_H2O, e_OH, e_CO2
70  pk_CO2 = 13
80  n_CO2 = 0.6
100 REM Generic rate follows
110 dif_temp = 1/TK - 1/281
120 BC       = ACT("Na+") + ACT("K+") + ACT("Mg+2") + ACT("Ca+2")
130 REM rate by H+
140 pk_H     = pk_H + e_H * dif_temp
150 rate_H   = 10^-pk_H * ACT("H+")^n_H / ((1 + ACT("Al+3") / lim_Al)^x_Al * (1 + BC / lim_BC)^x_BC)
160 REM rate by hydrolysis
170 pk_H2O   = pk_H2O + e_H2O * dif_temp
180 rate_H2O = 10^-pk_H2O / ((1 + ACT("Al+3") / lim_Al)^z_Al * (1 + BC / lim_BC)^z_BC)
190 REM rate by OH-
200 pk_OH    = pk_OH + e_OH * dif_temp
210 rate_OH  = 10^-pk_OH * ACT("OH-")^o_OH
220 REM rate by CO2
230 pk_CO2   = pk_CO2 + e_CO2 * dif_temp
240 rate_CO2 = 10^-pk_CO2 * (SR("CO2(g)"))^n_CO2
250 rate     = rate_H + rate_H2O + rate_OH + rate_CO2
260 area     = PARM(1) * M0 *(M/M0)^0.67
270 rate     = PARM(2) * area * rate * (1-SR("Albite"))
280 moles    = rate * TIME
290 SAVE moles
 -end

#In my literature

Albite
    -start
    10 REM PARM(1) = MSA (Molar surface area) [m^2/mol]
    20 si_alb = SI("Albite")
    30 if (M <= 0 and si_alb < 0) then goto 200             
    40 SA = PARM(1) * M             
    50 if (M = 0 and si_alb > 0) then SA = 1e-05  #nucleation
    #60 k_acid = 10^(-10.16)*EXP(-65.00e+03/8.314*(1.0/TK-1.0/298.15))*(ACT("H+")^(0.457))                 
    70 k_neut = 10^(-12.56)*EXP(-69.80e+00/8.314*(1.0/TK-1.0/298.15))
    #80 k_base = 10^(-15.60)*EXP(-71.00e+03/8.314*(1.0/TK-1.0/298.15))*(ACT("OH-")^(-0.572))
    90 k_rateconst = k_acid + k_neut + k_base
    100 r = k_rateconst * SA * (1-(10^si_alb))
    190 moles = r * TIME
    200 SAVE moles
    -end


[dlparkhurst]

The rate equation you site is from Sverdrup and Warfvinge, 1995, so you can check out that reference. There is also a compilation of rates by Palandri and Kharaka, where you can find a rate equation and a list of references that they used to arrive at their rate parameters.

There will certainly be variations among the differing rate expressions. I think all you can hope for is to bracket the results among the rate expressions that are available.

It is difficult to determine a reactive surface area, so any rate expression you use will also have that variable to consider.

Albite will not be reacting in isolation. You will have many options for the other primary and secondary minerals that are reacting. You must consider which other primary minerals are dissolving. In addition, if you look at the saturation indices for other minerals, your reaction solution will probably be supersaturated with SiO2 phases (quartz, chalcedony, others), gibbsite, clays, and other secondary minerals. Any of these could precipitate, but some are probably more likely than others. If you have mineralogy for your system, you may be able to narrow the selection. Your choice of these auxiliary reactions will affect the rate at which albite approaches equilibrium.

[dlparkhurst]

I'm not sure what you are asking. The reaction equations for minerals are usually defined in the database file, in your case, llnl.dat. The saturation index is the log10 of the ion activity product of the equation (assuming the pure solid has activity of 1.0) divided by the log K at the temperature of the calculation.

A mineral may be defined in EQUILIBRIUM_PHASES, in which case the mineral will dissolve or precipitate to equilibrium (SI = 0), or the moles of mineral will completely dissolve (SI < 0). It is also possible to set a "target saturation index" other than zero, which will cause the program to dissolve or precipitate to the target saturation index.

A mineral may be defined in KINETICS in which case, it will tend toward equilibrium with time. It is also possible that the kinetic reaction will be limited by the amount of kinetic reactant present.

If quartz is included in EQUILIBRIUM_PHASES or KINETICS, then it will dissolve or precipitate SiO2 to approach equilibrium. However, the saturation index of quartz will change, even if quartz is not included in EQUILIBRIUM_PHASES or KINETICS, provided there are any other silica containing minerals that are defined in EQUILIBRIUM_PHASES or KINETICS. In that case, there could be a number of reactions that affect the quartz saturation index, but quartz itself is not reacting.