KC

[snjaykdubey]

DATABASE C:\Program Files (x86)\Phreeqc\Databases\sit.dat
 
I cant run this program i hope if u can help

 kc = cm/sec is converted to mol cm-2 sec-1
Intial ferrous is 0.140 Mol/l

PHASES
mildsteel_waste
   Fe =   +1 Fe+2  +2e-
      log_k   12.75 # without importance
      delta_h   -94.218 # without importance
RATES
mildsteel_waste

-start
REM parm(2) = Reactive surface area (cm2 dm-3)

10  MD = 7.87  #gm/cc
20  Atwt = 55.845 #IronAtomicWt
30  Kc = 1.585489e-14 #units cm/sec
40 if (M <= 0) then goto 100
50 rate = -Kc
60 rate = rate*(MD/Atwt)

70 rate = rate*PARM(2)#kinetic rate in mol/s
80 moles = rate*TIME

100 SAVE moles
-end

SOLUTION 1

units   mol/L
pH      7.0
temp    25

Na 1.69e-1 #From BoundaryWater
Cl 1.60e-1 #From BoundaryWater

KINETICS 1
mildsteel_waste

-m   0.140
-m0  0.140
#-formula Fe -1  Fe+2  1  e-  2
-parms 7.776e6 90300
-step 7.776e6 in 100 steps
-tol 1e-15
INCREMENTAL_REACTIONS true


USER_GRAPH 1
-heading time Fe; -axis_titles days mol/L
  10 GRAPH_X TOTAL_TIME/86400
  20 GRAPH_Y TOT("Fe")
-end

END

[dlparkhurst]

You have a sign issue. Your SAVEd value is negative, so you are trying to remove Fe from solution, but there is no Fe in solution. I think you need to change the sign of your rate expression.

[snjaykdubey]

Dear Sir,

Thanks for your reply,
i made the following correction
i hope if you can go through it AND let me know if i did any mistake.

Problem
I would like to solve corrosion rate for ferrous.
Reaction : Fe = Fe2+ +2e-
Equation : dS/dt = - Kc
But: Kc = cm/sec and S= m
I would like to calculate corrosion rate in Fe mol m-2 sec -1

Graph Expected :  Fe conce vs Time

PHASES
mildsteel_waste
Fe = Fe+2 + 2e-
log_k 12.75
delta_h -94.218 kJ
RATES
Fe
-start
10 MD = 7.87
20 Atwt = 55.845
30 Kc = 1.585489e-14
40 if (M <= 0) then goto 100
50 rate = -Kc
60 rate = rate*(MD/Atwt)
70 rate = rate*PARM(2)
80 moles = -rate*TIME
100 SAVE moles
110 REM parm(2) = Reactive surface area (cm2 dm-3)
-end
SOLUTION 1
units mol/L
pH 7.0
temp 25
Na 1.69e-1 #From BoundaryWater
Cl 1.60e-1 #From BoundaryWater
EQUILIBRIUM_PHASES 1
magnetite            0.00 0.00
KINETICS 1
Fe
-formula Fe 1
-m 0.14
-m0 0.14
-parms 7776000 90300
-tol 1e-015
-steps 7776000 in 100 steps # seconds
-step_divide 1
-runge_kutta 3
-bad_step_max 500
INCREMENTAL_REACTIONS true
USER_GRAPH 1
-heading time Fe; -axis_titles days mol/L
10 GRAPH_X TOTAL_TIME/86400
20 GRAPH_Y TOT("Fe")
-end

awaiting for your reply,

Kind regards,
Sanjay

[dlparkhurst]

I'm not going to check your work. You are the one who knows what you want to calculate, I would only be guessing.