I recently tore down a flourite/dirt tank, and have been gradually trying to recover/clean the flourite.
I've just been letting the mix dry out, and then whenever I do a waterchange or something (I'm trying to just use waste water for this...), I'll dump it in the bucket/box with the mix, stir things up a bit, and then try and drain off as much 'floaties' as possible.
I think my flourite is relatively clean now - I wouldn't hesitate to reuse it, but I wouldn't feel comfortable selling it to someone else.
And I was dealing with regular flourite black. I imagine sand would be quite a bit slower and more problematic, but if you are patient, I imagine the same winnowing process will work, it'll just take a bit more time/effort.
I think letting it dry twixt rinsings may be helpful, as a lot of the dirt components tend to float if they aren't waterlogged...