React abandoning effort

[Sam]

I am trying to get react to generate a speciation diagram for Al+++,Al3((OH)4)5+,Al2((OH)2)4+,AlOH2+,Al((OH)2)1+,Al(OH)3,Al(OH)4- .In the command pane I put the following:

 

0.01 molal Na+

0.01 molal Cl-

10 mmolal Al(OH)4-

...Error Al(OH)4- needs to be swapped in to the basis

 

when I go to the basis pane to add Al(OH)4- or any other Al species or try to swap it I do not find it in the Aqueous list.So I have only Al+++, H+ ,Cl- and H2O in the basis.

continuing with the commands:

pH = 2

slide pH to 8

precip = off

go

 

Then I get the following message:N-R did not comverge after 400 its,maximum residual = 4.52 e+120,Xi=0.3400...--Didn't wake up,abandoning path.Please help.

[Sam]

I am trying to get react to generate a speciation diagram for Al+++,Al3((OH)4)5+,Al2((OH)2)4+,AlOH2+,Al((OH)2)1+,Al(OH)3,Al(OH)4- .In the command pane I put the following:

 

0.01 molal Na+

0.01 molal Cl-

10 mmolal Al(OH)4-

...Error Al(OH)4- needs to be swapped in to the basis

 

when I go to the basis pane to add Al(OH)4- or any other Al species or try to swap it I do not find it in the Aqueous list.So I have only Al+++, H+ ,Cl- and H2O in the basis.

continuing with the commands:

pH = 2

slide pH to 8

precip = off

go

 

Then I get the following message:N-R did not comverge after 400 its,maximum residual = 4.52 e+120,Xi=0.3400...--Didn't wake up,abandoning path.Please help.

[Brian Farrell]

Hi Sam,

 

A few things. Unless you're setting a free constraint, you typically set the component concentration, or total Al concentration, in the Basis. You can just add Al+++, H2O, H+, Na+, and Cl- to the Basis, and React will calculate the distribution of mass between all the possible species which can be formed from combinations of the Basis species, including the various Al species you mentioned below.

 

Basis swaps are performed when the default Basis set might not be the best way to describe your system. If a fluid is in equilibrium with quartz, for example, you would swap Quarts into the Basis and set its mass, rather than specifying the concentration of SiO2(aq). Since Al(OH)4- is prevalent at hight pH, you might swap that into the Basis in place of Al+++ if you are starting with a basic solution, but you're starting with an acidic solution here so there is no need to perform a basis swap, since the Al+++ is prevalent under acidic conditions.

 

Oftentimes when people make speciation diagrams like this they choose to turn charge balance off. In reality, of course, electroneutrality must be maintained, but in a simple model like this where you're only looking at Al speciation this may not be necessary.

 

I think another issue is the high concentration of Al you've set in the Basis. Is this realistic for your system? Since you've turned mineral precipitation off, minerals like Gibbsite become supersaturated very quickly.

 

You might try using Act2 to create similar diagrams. The one in Figure 5.4 b might be helpful to you (just remove the SiO2 from the system). That will show you how concentration/ activity and pH affect the speciation of Al.

 

Do you know why all of your posts are showing up twice?

 

Hope this helps,

 

Brian Farrell

Aqueous Solutions LLC