"Repeated restart of integration."

[Hosseif]

I'm doing reactive transport modeling in which phreeqc has been coupled to a transport solver. I'm simulating dissolution of a mineral according to reaction A(s)=A(aq). It's a kinetic reaction and rate = kS(A-A_eq). initial solution in the domain is A=0.001 and I inject a solution with A=0.002 and dissolution happens. at some points in the simulation I'm getting an error saying ""Repeated restart of integration.""

What could be a possible reason for that?
This is part of my phreeqc input:

SOLUTION_MASTER_SPECIES
[A] [A] 1 1 1

SOLUTION_SPECIES
[A] = [A]
log_k 0



PHASES
[A]_decay
[A]=[A]
log_k 0


SOLUTION 0
units mol/kgw
[A] .002

END

SOLUTION 1
units mol/kgw
[A] .001

END


RATES
[A]_decay
-start
10 if KIN("[A]_decay")>0 then rate = ( TOT("[A]")-.001 )* 50
20 moles = rate * TIME
30 SAVE moles
-end
END


KINETICS 1
[A]_decay
-m 0.1
-cvode true
END



Best,
Hossein

[dlparkhurst]

The sign of moles is important. The sign of moles times the coefficient in formula determines whether the concentration of [A] increases or decreases. I have rewritten your RATES equation so that [A] is removed from solution if the concentration is greater than 0.001 and removed if less than 0.001.


SOLUTION_MASTER_SPECIES
[A] [A] 1 1 1

SOLUTION_SPECIES
[A] = [A]
log_k 0

PHASES
[A]_decay
[A]=[A]
log_k 0

SOLUTION 1
units mol/kgw
[A] .002
END

RATES
[A]_decay
-start
#10 if KIN("[A]_decay")>0 then rate = ( TOT("[A]")-.001 )* 50
10 rate = ( 0.001 - TOT("[A]"))* 50
20 moles = rate * TIME
30 SAVE moles
-end
END

USE solution 1
KINETICS 1
[A]_decay
-formula [A] 1
-m 0.1
-step 1
-cvode true
END

[Hosseif]

Dear David,

Thank you so much.

I just ran the rewritten phrqc file by you. It leads to precipitation of [A]_decay phase while I'm looking for dissolution of [A]_decay phase.

[dlparkhurst]

Then start with a solution with a small [A] concentration.