I don't know about quail but I did have them for a short period of time and I put a small pan in the pen with sand and a little DE mixed with in and they loved it. They would get in there and dust all the time. I don't know if they really needed it but it didn't hurt.
Like everyone else has said, they love sand/dust boxes. I put one in each of my pens every so often, and I just use sand from a naturally sandy knoll close to the pens. I wonder sometimes if they don't ingest as much as they kick out while doing their bathing. I really keep it on hand for them in the summer months when I give them my bad tomatos from the garden.............(it's their seed-grinder
Don't need it but they love it. I notice I get more eggs when they have sand in their boxes. It's where they can hang out, lay their eggs.
Go to safety if something is after them from the bottom. They get their treats there. In my case a spray of Millet once in a blue moon (tomatoes hugh, hum).
Ya, the DE helps keep ants away and other little pesky critters too.
They'll sing for you when they are happy happy.
I buy a bag of play sand every month for them. Don't have a sandy knoll. But I have been known to just use sandy dirt mixed with the sand when I am running low. Cause I want those eggs.
I think once you start them on sand boxes, they hold their eggs ransom for more sand. Smart birds, huh.
I didnt have any sand but I did have a bag of cheap potting soil that was dried out, they went nuts. My birds had never seen dirt before. There was a brawl to see who was in the box next, could only hold 5 birds at a time.... Bill