Assuming from your post that this was "officially" donated, do you happen to know if they had the jump through any hoops to get around the risk of getting done for illegal waste disposal?
One if the mums on the school run works in the office at our local Hanson's quarry (we'll one of them...) and she's offered to try sorting some belt, but wasn't sure if they'd have issues as it's classed as waste.
Previously, I've just got it from the lads working the quarry floor who don't give a toss about the regs, so long as they don't get caught, but my contact has since moved on...