Kozoite log K recalculation

[Kaizen]

Hi, 

I added a new mineral, kozoite into my database using the reaction: LaOHCO3 = La+++ + OH- + CO3--.  Upon entering the log K of -24.3 and the "Species in reaction" pane of La, OH and CO3, there was an automatic recalculation to give a reaction: Kozoite + 2H+ = La+++ + H2O + HCO3- with a new log K of +3.2239.  Please refer to the attached screenshot.  I gather that this was all done to reflect a dissolution reaction via H+ addition but I am wanting to check that I did not introduce an error along the way and I am okay to proceed.  

Many thanks for any advice/feedback

[Jia Wang]

Hello Kaizen,

The GWB apps expect all reactions to be written in terms of basis species, so TEdit performs reaction balancing to swap out the aqueous species to do so. Please see 9.2.7 Basis swapping in the GWB Essentials Guide for a description and example. I used the thermo.com.V8.R6+.tdat dataset and tested out the procedures you described and I got a different result. But that can be due to different Log K values for the carbonate and hydroxyl reactions that you might have entered in your database different from the default values? You can check your entry using Rxn, by swapping CO3—and OH- for HCO3- and H2O respectively, to see if you get the original Log K value when you balance the equation. See section 4.1 in the GWB Essentials User's guide for more information on Balancing reactions in Rxn. Please attach your database if you need further assistance.

Best,

Jia 

[Kaizen]

Hi Jia, 

Thanks for the prompt response.  I am going to add in some other minerals so best I get this right before I proceed further.  Attached is the modified database for you to check. 

The original reaction as entered is: LaOHCO3 → La + OH + CO3 logK = −24.1 ± 0.3

Many thanks

thermo.com.V8.R6+.tdat

[Kaizen]

On 10/16/2019 at 11:12 PM, Jia Wang said:

Hello Kaizen,

The GWB apps expect all reactions to be written in terms of basis species, so TEdit performs reaction balancing to swap out the aqueous species to do so. Please see 9.2.7 Basis swapping in the GWB Essentials Guide for a description and example. I used the thermo.com.V8.R6+.tdat dataset and tested out the procedures you described and I got a different result. But that can be due to different Log K values for the carbonate and hydroxyl reactions that you might have entered in your database different from the default values? You can check your entry using Rxn, by swapping CO3—and OH- for HCO3- and H2O respectively, to see if you get the original Log K value when you balance the equation. See section 4.1 in the GWB Essentials User's guide for more information on Balancing reactions in Rxn. Please attach your database if you need further assistance.

Best,

Jia 

Looked at Rxn (screenshot attached) and seems okay, but appreciate if you could check the database previously attached. 

[Jia Wang]

Hi Kaizen,

Thanks for attaching the file and the additional Rxn screenshot. The Log K value in reaction balancing using Rxn should match the resulting Log K for the mineral in TEdit. I see that the Log K value from reaction balancing using Rxn is -21.1 at 25C, which does not match the initial Log K value of -24.3 in your original post above. Using the database attached, I tried adding the kozoite into the database with the Log K value of -24.3 for the reaction LaOHCO3 = La+++ + OH- + CO3—and got 0.0289 as the new resulting Log K value for the reaction Kozoite + 2H+ = La+++ + H2O + HCO3-.  Perhaps you entered -21.1 for your Log K value accidentally when you were creating the new mineral instead of the intended Log K of -24.3? You can modify your entry by deleting the basis species under ‘species in reaction’ and then re-enter the correct Log K value and select the corresponding aqueous species(CO3—and OH-) and basis species (La+++). You can also simply delete the entry and re-add kozoite as a new mineral.

Hope this helps.

Best,

Jia

[Kaizen]

Thanks, seems to be working now.  Appears that I entered -21.1 instead or the correct -24.1 log K.  Running in Rxn and swapping out the species gives the correct log K. Many thanks for your help!