Jump to content

React problems


 Share

Recommended Posts

HI,

 

i am having problems with some calculations in react,

I am making a pH sliding of Zn++, i put the calculations with charge balance of Cl- and without charge balance.

 

I get error for the charge balance, and the calculations stop for the pH of ~8.5

 

"Caution: molality of Cl- component forced negative by charge balance: -2.782e-007

*N-R didn't converge after 400 its., maximum residual = 4.83e+121, Xi = 0.5800

 

Cutting step size to find solution

Residuals too large, 662-th interation

-- Didn't wake up, abandoning path"

 

For the sliding without the balance using react and even SpecE8 it can't compute from pH ~12.5 to ~13.8 but can compute for pH of 14.

Why is that?

 

I also find out that if i change the delxi from 0.01 to 0.001, making more dots the programs crushs and stops the compute arouth pH ~3.5 - ~6. Why is that? shouldn't it calculate the same for all?

with_CB.rea

without_CB.rea

Link to comment
Share on other sites

Hi:

 

Apologies for the delay.

 

In your first script, as the error message indicates, you run out of Cl- for charge balance, and it is forced to negative concentrations. You can remedy this by either beginning with a higher anion concentration, or better yet, consider a base titration (NaOH for example), rather than a pH slide, as this avoids negative concentration issues. Unless this is a pure solution, it's a good idea to have some background electrolytes (Na, Cl).

 

The issue with the smaller reaction path steps occurs right when Zincite reaches saturation- you are essentially removing 1/10th the proton mass at each step, and this creates an unstable matrix when Zincite becomes supersaturated and React attempts to swap it in for the Zn++ matrix component. I'm not sure exactly why this happens, but this model is being run with a large charge imbalance- I recommend fixing the first model, with charge balance, as this should result in a model that is more stable overall. The same goes for the non-convergence issue at high pH.

 

I hope that helps,

 

Tom Meuzelaar

RockWare, Inc.

RockWare, Inc.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
×
  • Create New...