Text book chemistry example AgCl precipitation

[mac]

Hi,

I am trying to set up a very simple model for a classroom excercise on solubility using specE8. Later, I intend to have the students mix AgNO3 + KCl and have a look on solubility / residual Ag concentration etc. To start, i added only Ag / Cl into water.

database: thermo_minteq.tdat

add 0.1 mol / L Ag+, & Cl-

use H+ to balance charge.

 

The results show that Cerargyrite is oversaturated, yet there are no minerals in the system.  This is puzzling me, considering the low solubilty of AgCl in water (+low Ksp in database). When i do an activity plot, Cerargyrite shows up (with max conc. of dissolved Ag ~ 10^-4,5)

 

I am aware this is a very basic question, but maybe somebody could help me out? Why dont i get solid AgCl in specE8

Thanks and best regards,

Mac

 

 

 

 

AgCl.txt Act_AgCl.ac2 AgCl.sp8

[Jia Wang]

Hello Mac,

Thank you for posting your files. If you are using SpecE8, you will not observe mineral precipitation. SpecE8 calculates the chemical mass distribution of a fluid in a static system and does not allow minerals to precipitate. In the GWB, you can model a single-node dynamic system using the React application.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

 

[Jia Wang]

Hello Mac,

Just to follow up on my previous message. If you are only interested in looking at the solubility of minerals, you can use SpecE8 and swap the mineral of interest into the Basis and calculate fluid speciation. Please see section 7.2 Equilibrium Models in the GWB Essentials User Guide for further explanation on how swapping works.

Hope this helps,
Jia

[mac]

Dear Jia,

 

Great, thank you for your help and the hint on using SpecE8 for checking solubility !

 

Cheers,

mac