I can offer a little insight. One of the companies I work for buys salvage/returned merchandise (mostly electronics, computers and related devices, office furniture, appliances, etc). We go through the items sorting out what is worth reselling as is, what requires further inspection and repair, and obvious junk beyond repair. The items requiring inspection and/or repair go to me, and about half of what I look at is considered "open box" or "damaged box", gets a cursory inspection, is run though the paces and checked for functionality, and sent on to the people who list it on various online marketplaces. About a fourth of the remaining items sent to me are repairable, which I do and send on to the sellers listed as "seller refurbished". The remaining portion is sent to the junk pile if I can't repair it or if it's missing too many parts to be worth selling. I will sometimes hold back a valuable part (power supply, special cable, etc) from an unsellable part to use for a similar item in the future.
From the junk pile, we sell by weight to recyclers who either break the items down into recyclable parts themselves, or sell them on to firms that handle what they can't, including extracting rare metals from circuit boards. To my knowledge, such firms are based here in the US, but I don't know enough about that side of the chain to name any.