PhreeqcUsers Discussion Forum

Beginners => PHREEQC basics => Topic started by: tianshiyu on October 17, 2019, 09:01:22 AM

Title: Saturation index
Post by: tianshiyu on October 17, 2019, 09:01:22 AM
First, I want to thank dlparkhurst for helping me. But I couldn't reply to you in my last post, I had to created a new post.Now I have another problem need to consult you. I use EQUILIBRIUM_PHASES to make the SI=0(hydroxyapatite), but hydroxyapatite only settle at a High supersaturation and I didn't know the value. So in the simulation process, the hydroxyapatite will settled at a low pH(pH6-7) than reality(pH7-9). Is there any way to make the simulation more realistic?
thank you again for your reply.
Title: Re: Saturation index
Post by: Pak on October 17, 2019, 12:54:09 PM
Maybe changing the themodynamic equilibrium constant? not sure.
Title: Re: Saturation index
Post by: tianshiyu on October 17, 2019, 02:21:35 PM
But the themodynamic equilibrium constant is the database default. Is there any method to change it?
Title: Re: Saturation index
Post by: dlparkhurst on October 17, 2019, 02:57:59 PM
You can use a PHASES data block in your input file that redefines the phase with a different equilibrium constant. Just copy the definition from the database and put it in your input file.

The equilibrium constant for hydroxyapatite does vary among the databases, so varying within that range may be reasonable. If you need to change the log K more than that, you may be missing something.
Title: Re: Saturation index
Post by: tianshiyu on October 19, 2019, 07:18:32 AM
Thank you a lot. I think I might have a clue!