Simulating change in SI as a function of pH over time

[DyliS]

Hello,

I am trying to simulate the change of SI of MSH phase over time as a function of pH. I've attached the input file and the modified database that is being use to carry this out. When I run this input file, I keep getting the same error pasted down below. I'm not sure what the problem is after fixing this error or the syntax I have might be throwing this error as an accident.  Any guidance will be appreciated.

Thank you
~Dylan

(
ERROR: Syntax_error : missing " or ( in line:
ERROR:  in BASIC line
 20   if (SI("M075SH") => 0)then goto 100
ERROR: Fatal Basic error in rate Periclase.
)

[dlparkhurst]

You need to use ">=" rather than "=>".

Also need to remove spaces after the hyphens in the KINETICS definitions.

This code runs, but periclase is supersaturated, so the RATES expression always evaluates to zero.

Code: [Select]

SOLUTION 1
    temp      25
    pH        7 charge
    pe        4
    redox     pe
    units     mmol/kgw
    density   1
    Na        10
    Si        5
    N(5)      15
    Mg        30
    -water    1# kg

RATES
    Periclase
-start
  1   rem PARM(1) = normalized surface area
 10  if (M <= 0)then goto 100
 20  if (SI("M075SH") >= 0)then goto 100
 30  si_MSH075 = SI("M075SH")
 40  if M > 0 then area = PARM(1)*M
 50  rate = 10^(-0.9877436 * (-LA("H+"))- 3.9806115) * area
 60  moles = rate * TIME
100 SAVE moles
-end

KINETICS 1
 Periclase
  -tol 1e-8
  -m0  0
  -m  6.38e-3
  -parms 3.005e5 # normalized surface area (cm^2)
  -steps 3600 in 10 steps # steps are in seconds, 10 hours

USER_GRAPH 1
-headings Reaction MSH(0.75) MSH(1.5) Brucite pH
-chart_title "MgO Dissolution"
-axis_titles "Time (s)" "Saturation Index " "pH"
-initial_solutions true
-start
10 graph_x  SIM_TIME
20 graph_y SI("M075SH") SI("M15SH") SI("Brc")
30 graph_sy  -LA("H+")
-end


[DyliS]

Thank you for your help!

[Erdinc]

Hello David,

One of the mineral that i have in my slag is Periclase. I struggle to find rates block for this mineral. I saw on one of the post that you have RATES of Periclase. Can I please ask the source of this data below and can i use it?

thank you.


RATES
    Periclase
-start
  1   rem PARM(1) = normalized surface area
 10  if (M <= 0)then goto 100
 20  if (SI("M075SH") >= 0)then goto 100
 30  si_MSH075 = SI("M075SH")
 40  if M > 0 then area = PARM(1)*M
 50  rate = 10^(-0.9877436 * (-LA("H+"))- 3.9806115) * area
 60  moles = rate * TIME
100 SAVE moles
-end

KINETICS 1
 Periclase
    -tol 1e-8
    -m0  0
    -m  6.38e-3
    -parms 3.005e5 # normalized surface area (cm^2)
    -steps 3600 in 10 steps # steps are in seconds, 10 hours

I have calculated my moles and area for periclase as per below.
25.2 mol/L
0.699m2/L

Periclase
    -formula  MgO  1
    -m        25.2        mol/L
    -m0       25.2       mol/L
    -parms    1 0.699 2    (m2_periclase/L_pores)
    -tol      1e-08

[dlparkhurst]

The rate equation was given in the original post. I do not know the source. They were using a modified version of the Cemdata thermodynamic database. Perhaps you can track it down through the literature. There is an article on Cemdata18 in Cement and Concrete Research.

Alternatively, Palandri and Kharakha provide a rate for Mg(OH)2 that you could potentially use. Chen ZHU has compiled rates in PHREEQC format from P&K as well as other sources. I think you can find a download at https://hydrogeochem.earth.indiana.edu/index.html.