PhreeqcUsers Discussion Forum

Processes => Dissolution and precipitation => Topic started by: PabloCM on August 11, 2015, 02:12:48 PM

Title: Convergence problem
Post by: PabloCM on August 11, 2015, 02:12:48 PM
Hi,
I was trying to graph the solubility of Fe2(SO4)3 as a function of pH using the database llnl.dat, but I came across many convergence errors with my input file.
Any help is welcomed.
Thanks!
Title: Re: Convergence problem
Post by: dlparkhurst on August 11, 2015, 04:31:12 PM
Your mineral is too soluble for the aqueous model. The ion-association models (like llnl.dat) are not adequate for the high concentrations that are generated.  Here is a calculation that goes up to 10 molal, the pH goes down to about 0.2 because of Fe-OH complexing, and the mineral is still 6 orders of magnitude undersaturated.

SOLUTION 1
   -temp 15
   -pe 10
   #-water .1
   -pH 8
   O(0)   1   O2(g)   -0.7
INCREMENTAL_REACTIONS
REACTION
Fe2(SO4)3 1
10 in 10 steps
USER_GRAPH 1
   -headings pH x
   10 graph_x -act("H+")
   20 graph_y LOG10(tot("Fe"))
END
Title: Re: Convergence problem
Post by: PabloCM on August 13, 2015, 12:05:09 PM
Thank you very much for your reply.