A quick search suggests that most "weeded" books are sold on or donated rather than burnt or sent to landfill. Do you have sources that say otherwise?
Ours has a volunteer run used bookstore that sells a few for pennies on the dollar. Vast majority are shredded
Just go to a local library and ask a librarian or anyone who has a lot of books and tries to give them away; sadly, in most cases, they pick the valuable ones, and the rest just get sent for destruction (Burning).
It is pretty standard procedure.