PhreeqcUsers Discussion Forum

Processes => Inverse modelling => Topic started by: BalabaJ on March 17, 2017, 04:19:44 PM

Title: Inverse Modeling for a leaching study
Post by: BalabaJ on March 17, 2017, 04:19:44 PM
Hi Mr. Parkhurst,

I am trying to use the inverse modeling to predict what minerals had participated in a leaching experiment.  I ran into some convergence problems with the model that I setup for the task. The input file is attached for your review. 

I have tried several things including adding the fictitious aqueous species ("SOLUTION_SPECIES H2O + 0.01e- = H2O-0.01 log_k   -9.0), increasing the iterations to 200, and decreasing the converge tolerance.  None of the above seems to help solving the problems. 

Could you please shed some lights on the problems?   

Thank you.

Best,
Jason   
 
Title: Re: Inverse Modeling for a leaching study
Post by: dlparkhurst on March 17, 2017, 06:14:55 PM
A couple of things. The program is failing on the speciation of solution 2. First, the pH is >12, which results in a high OH- concentration, such that I think the OH- contribution to alkalinity is greater than the input alkalinity. If that is the case, the program fails. Second, I don't think it is possible to charge  balance with pe for this water. In general, it would be a very unusual situation where it makes sense to try charge balancing with pe.
Title: Re: Inverse Modeling for a leaching study
Post by: BalabaJ on March 17, 2017, 07:55:01 PM
Indeed, it should be unusual using pe to balance charge balance.  Thank you for pointing it out.

I have updated the input file and it passed the solution stage.  However, the simulation was now not able to balance both solutions.  I changed the uncertainties but it was not able to resolve the errors. 

Could you please point out what might have caused the problem?

Thank you.

Best,
Jason
Title: Re: Inverse Modeling for a leaching study
Post by: dlparkhurst on March 20, 2017, 07:34:56 PM
Your analyses do not balance very well. The first solution charge balance is -36% and the second is -25%. Check your analyses. Analyses should balance to less than 10%.
Title: Re: Inverse Modeling for a leaching study
Post by: BalabaJ on March 25, 2017, 12:28:55 PM
Thank you, Mr. Parkhurst.  It is what happened.