rate of basalt glass dissolution

[Anvj0705]

I am trying to calculate rate of dissolution of basalt glass using existing model. I put my initial parameters. Now question is, how to print rate in output file?

TITLE Glass_Basalt dissolution rate

SOLUTION 1
 temp 90
 ph 8.7 charge
 units mmol/kgw
 Na 5.011e-5   

SAVE SOLUTION 1
END

USE SOLUTION 1
Kinetics 1 define Glass parameters
 Glass                                    # Name of phase
    -formula    Si1Ti0.03Al0.307Fe0.183Mg0.186Ca.206Na0.091K.009O3.169 1    # Glass formula
   -m0         1                                                   # Initial moles of mineral
    -parms      0 2.706 0                                                  # Three parameters as explained below as 4.509 m2/g surface area
 -steps 1972800 in 47 steps #24 days
  INCREMENTAL_REACTIONS TRUE
  SOLUTION_SPECIES
SAVE SOLUTION 2

RATES
Glass #SiTi0.03Al0.31Fe0.18Mg0.19Ca0.21Na0.09K0.01O3.168, M 114.08 g/mol

-start
2 if (PARM(1) = 0) then  goto 3 else goto 5
3 if PARM(3) = 0 then S = PARM(2) * m * 114.08 else S = ((m/m0)^(2/3)) * 144.08 * PARM(2)
4 GOTO 1000
5 S = PARM(2)*TOT("water")
##------------------Kinetic calculation---------------------##
      # parameters
1000 if (m0<=0) then go to 5000
1001 Aa = 1.08e-4   #mol.m-2.s-1
1003 Ea = 21500   #J.mol-1
1006 R = 8.3144 #J.deg-1.mol-1
1007 ACTI = (ACT ("H+")^3)/(ACT("Al+3"))
1008 n = 1/3
1009 Sig = 1
      #rate equation
2000 rplus = Aa * ACTI^n  * exp(-Ea/ (R * Tk)) * S
3000 rate = rplus * (1 - (SR ("Glass")^(1/Sig)))
4000 moles = rate * TIME
#5000 SAVE moles
6000 SAVE rate
-end

SELECTED_OUTPUT
     -file Glass_rate.txt
     -reset false
USER_PUNCH
     -headings Time(year) SI(Albite) pH Tot_SiO2 Tot_Al TOT_Na rate
     -start
     10 punch TOTAL_TIME/31556925 SI("Albite") LA("H+")*(-1) TOT("Si") TOT("Al") TOT("Na") "rate"
     -end
END     

[dlparkhurst]

I don't have your PHASES definition for the mineral GLASS, so I cannot run the script that evaluates SR("Glass").  Here are some comments.

You should multiply the rate by the internal variable TIME in the rates definition. Use line 5000, not 6000.

If you want to print the average rate for the glass kinetic reaction over a time step, you can use the Basic functions KIN_DELTA and KIN_TIME.

Code: [Select]

20 PUNCH KIN_DELTA("Glass") / KIN_TIME # mol/second

The Basic function KIN("Glass") will give the amount of kinetic reactant at any point of the calculation.

[Anvj0705]

Thank you for your valuable comment.

 The basic functions KIN_DELTA and KIN_TIME is working very well.

But I still didn't get rate definition?
Here, when I am using "5000 SAVE moles"- I am getting different mole of elements than using "SAVE rate" command.

Here I am sharing PHASE of Glass which is taken from Carbfix.dat

Thanks for your critical comments in advance...

Code: [Select]

Glass
Si1.00Al0.35O2(OH)1.05 + 0.35 OH- = 0.35 Al(OH)4- + SiO2
log_k -2.36449
-analytic 77.82514814711445 0.032450265390183614 -1502.5932036570116 -33.02705435543141 -216815.051931841 -7.454186812457974e-6


[dlparkhurst]

RATES expects SAVE to be the moles of reaction that are reacted over a time subinterval given by the variable TIME. Almost always SAVE is calculated as a rate times TIME. So, the units for SAVE are moles, not moles per second. Naturally, you will get a different result if you SAVE different values during a run.

Plot KIN("Glass") to see the amount of  glass remaining to be reacted (moles), and plot KIN_DELTA("Glass")/KIN_TIME to see the rate of glass consumption (mol/sec).

Note that you can use PRINT statements to debug or clarify what is going on in the RATES definition. The PRINTed results will be in the output file.

[Anvj0705]

Thank you for valuable response.

I have a problem with an experiment result.
In my experiment, I tried to calculate rate of dissolution of basalt glass rock (Amorphous) with respect to silicon, experimentally. Here I can't neglect the secondary phases. Element concentration in reactive solution was collected with time. With time concentration is increasing but there is a sudden fall due to SI of certain phases and constant for the time being, then it increases with time.
I collected chemistry of secondary phases using SEM-EDX. I am getting some crystalline and amorphous phases as secondary product due to glass dissolution.

I want to modal my experimental result.

How to select phases in EQULIBRIUM PHASES with solution considering crystalline and amorphous phases?

[dlparkhurst]

To use EQUILIBRIUM_PHASES, you need to have definitions in PHASES for all of the minerals that you want to include. To define a mineral in PHASES, you need a balanced chemical reaction and an equilibrium constant at the temperature(s) at which the reactions occur.

I don't know whether you will have all of the necessary information for the amorphous and crystalline phases that are produced. It may be that the secondary phases are also precipitating kinetically, which would require additional rate expressions for these phases.

Assuming you have complete analytical data at various point in the dissolution of glass and you know the stoichiometry of the secondary phases, you could rough-in definitions of PHASES and do speciation modeling to see if there are constant Ion Activity Products for these phases.

I might try a little bit of INVERSE_MODELING. The data requirements are simpler, in that you don't need an equilibrium constant, only the stoichiometries of the phases that are reacting. In concept, you should be able to calculate inverse models for how much of each phase reacts to produce each time point when you have chemical analytical data. You do need complete analytical data to do the inverse modeling. Ideally, you would get consistent mole transfers of glass and secondary minerals as a function of time. These time series could lead to quantification with equilibrium or kinetic modeling. It sounds simple, but inverse modeling can be harder than it seems. I would not spend too much time on it, but it should give you a sense of whether the system is working the way that you expect.