Database selection for solid precipitation

[IliasBouchkira]

Dear all,

Currently, I'm working on the study of fouling phenomena involved in the wet-process phosphoric acid, which consists of leaching a phosphate-containing mineral using sulfuric acid, the phosphate ore contains mainly (P, Ca, F, Si, Mg, Al, Fe), and sulfuric acid favors the S(6).

I would like to perform simulations and to predict the main solid phases that can precipitate during this digestion reaction throughout predicted saturation indices. I'm wondering which Database is more accurate for these simulations? Is there any advice...

Thank you in advance;

 

[dlparkhurst]

The pitzer.dat database would be the most suitable because it is accurate to higher ionic strengths. However, pitzer.dat does not include the elements P, Al, or Fe; so, unless you find or estimate Pitzer parameters for these elements, you will have to use another database.

The ionic strengths and high concentrations make the activity corrections for ion-association models suspect. Sit.dat is kind of an intermediate between the Pitzer approach and ion-association. I would probably run simulations with phreeqc.dat or wateq4f.dat, llnl.dat, and sit.dat, comparing results frequently. Where possible, I would compare a simplified system between these databases and pitzer.dat.

I think any calculations would be "semi-qualitative" at best. Any experimental mineralogy or X-ray diffraction of actual solids would be much more reliable.

[MichaelZ20]

Pitzer databases for PHREEQC from THEREDA (https://www.thereda.de/en/) may help you.

[IliasBouchkira]

Dear all,

Thank you for your answers; I performed many simulations using different Databases, I believe that the Pitzer Database is the most accurate, some recent works of my supervisor were related to the estimation of the Pitzer parameters for phosphate, and we included them to the database.

I have one more question related to the predicted phases, i don't know the difference between (SiO2(a), SiO2(am), Cristobalite, and Chalcedony) especially that they are defined in the phase part by the same reaction: SiO2 + 2H2O = H4SiO4

Are there any papers to read to understand the difference between them?

Thank you so much in advance.

[dlparkhurst]

The various SiO2 phases represent different crystallinities and, consequently, different solubilities (log Ks) of the solid. You can track down references for some of the phases from the citations in the WATEQ4F manual--https://pubs.er.usgs.gov/publication/ofr91183.