Surface complexation

[Kirkoff Xn]

Hi there,

I am trying to rework example 10.4 in the Geochemical and Biogeochemical Reaction Modeling book. On Table 10.1, I have hard time to understand how you found % of sites. 

E.g. the first weak site species, >(w)FeOH2+, Its concentration is 1.232 mmolal. I know that its site density is 0.2 mol/mol mineral. Can you elaborate how you found  65.9% here? 

Thanks

 

[Kirkoff Xn]

Along the same lines, I would like to know how you calculated the Maximum sorbed and metal concentrations in solution [mg/kg] based on below attached table (retrieved from https://academy.gwb.com/acid_drainage.php)

[Jia Wang]

Hello,

The % of sites is the concentration of the weak site species divided by the total concentration. On the table, you can see that the total concentration is 1.871 mmolal. If you divide 1.23 mmolal byt 1.871 mmolal, you get 0.657. If you run the simulation in the example and use Gtplot to export the numerical data for species concentration to Excel, you can calculate the percent for each surface species. The exported values carry more significant digits and you will see that they match the rounded values in the % of site column. More details regarding exporting numerical data from simulations can be found in section 8.5 in the GWB Essentials User Guide.

With regards to how the table of maximum concentration of metal sorption was calculated in the Co-precipitation example, please see this post.

Hope this helps,
Jia Wang
Aqueous Solutions LLC