I am trying to fit reaction parameters for experimental results, and I see that I need some help in understanding the process.

My experiment consists of injecting a solution of nanoplastic particles (the studied material) and bromide ions (as conservative tracer) into fully-water-saturated soil column. Just to make it clear -

**I want to model the affinity of the nanoplastic particles to the soil**.

I have managed to model my results for the bromide tracer, and obtained a ro and dispersivity values, which I understand I can use for the nanoplastic particles (but I'm not sure how...)

So, after following tutorials and some basic guidance from colleagues, I think I got most of the settings right (but I don't know for sure).

Assuming I did, here are the things I am not sure about:

1. In the "Solute Transport - General Information" section - which model should I choose for the nanoplastic particles? I am injecting my study solution into a saturated soil column, from bottom to top, at a relatively low flow rate (1 mL/min).

2. In the "Solute Transport - Reaction Parameters" section - which parameters I should check for 'fitted'? Like I mentioned, I already have solid ro and Disp. values from the tracer model. So depending on the answer to the first question (which model?), how should I proceed to choose the parameters? Which ones should I use and which should I leave at zero? And which should be fitted?

I hope this question is not too much trouble and can be answered (at least partially) through the forum. If some details are missing in order to answer it, please let me know and I will provide them.

Thanks in advance,

D.