High ionic strength surface complexation model

[JRen]

I am working on a surface complexation model with very high ionic strengths. I am utilizing ionic strengths between 0.5 M and 6.65 M.

Is the Pitzer database the most appropriate option in this ionic strength range for a surface complexation model? Also, can the Pitzer database be utilized with arsenate?

[dlparkhurst]

The Pitzer database is the most appropriate database for that ionic strength range.

However, nor arsenic redox state is included in pitzer.dat. You don't have many good options. It may be possible to find Pitzer parameters for arsenate, especially if you have a simple medium (single dominant cation-anion solution). If you have to use an ion-association model, you will be best off if the medium is NaCl because many of the activitiy coefficients are fit to sodium chloride solutions.