PhreeqcUsers Discussion Forum

Beginners => PHREEQC basics => Topic started by: JW on April 06, 2020, 09:33:35 AM

Title: Error in a simple solution with Exchange site
Post by: JW on April 06, 2020, 09:33:35 AM
I would like to simulate just a simple solution; a solid who has exchange site is added into a pure water.
So, I coded as follows with the database, llnl.dat.

SOLUTION 1
   ph 7 charge

EXCHANGE 1
   X 1

But, it resulted in a convergence error.

Please, let me know what is wrong in the code.
Thank you in advance.
Title: Re: Error in a simple solution with Exchange site
Post by: dlparkhurst on April 06, 2020, 03:38:40 PM
What cations will fill the exchange sites? Considering the database you are using, which exchange reactions would be applicable?
Title: Re: Error in a simple solution with Exchange site
Post by: JW on April 07, 2020, 01:42:11 AM
I see.
I had to define associated cations in SOLUTION when EXCHANGE was defined.
OK. Thank you.
Title: Re: Error in a simple solution with Exchange site
Post by: dlparkhurst on April 07, 2020, 02:43:42 AM
Yeah, phreeqc.dat does not have a definition for HX (it is commented) and H+ is the only cation in your solution. So, you could define or uncomment the HX reaction, but that would give you an inititial exchange composition of HX, which is unrealistic. Better to initialize with a a solution that has a plausible cation.

You can initialize the exchanger without equilibrating with a solution:

Code: [Select]
EXCHANGE
NaX 0.5
CaX2 0.1
END