Unexpected pH drop with increasing W:R

[Sanjoy]

Hello GWB support,

 

I'm investigating the change in fluid pH associated with water-rock reactions with changing water-to-rock ratio (W:R) and temperature. I find that the pH change tracks nicely with the formation of a particular mineral but there is a sudden drop in pH going from W:R = n to W:R = n+1 that I cannot explain. It happens at both high and low temperatures, at the same W:R. I originally thought it was some kind of mineral buffer effect, but I have suppressed everything I could think of to simplify the problem as much as possible following advice from Brian F., but this jump still baffles me.

 

I'd very much value your insight.

 

I'd rather not post my script here, but would be happy to email it to you, as well as xls file with the data plotted.

 

Thanks!

[Brian Farrell]

Hi Sanjoy,

 

If you'd prefer, you can send your script to support@gwb.com. We're currently teaching a Reactive Transport Modeling short course in Australia, but we'll try to take a look at this as soon as we can.

 

Cheers,

 

Brian Farrell

Aqueous Solutions LLC