Using Bitman / Cannan as my 2 references with the newer miners with the built in power supplies.
75% or more of the weight is aluminum for the heatsinks and case. Which is totally and easily recyclable.
15% to 20% is the power supply and some steel which are also recyclable in just about any part of the world.
The rest? The circuit boards and chips and other stuff. Yes, it takes a bit more to recycle it, but it's done all over the world every day.
Just because it can be recycled doesn't mean that it would be. Recycling metal is quite a tedious task and many a times, it makes far more sense economically to just throw them to a landfill and mine for new material than trying to waste money and recycle them. E-waste is quite a prominent issue because parts of it are either hard to recycle or expensive to do so, due to the miscellaneous costs incurred in the process as well. Recycling doesn't really do all that much, it doesn't offset the environmental impact from mining it in the first place and incurs even more through the process of recycling it...
The circuit boards are the hardest to recycle and may or may not be.
The same with the power supply and the other small components.
The aluminum is quick and simple.
And on older miners makes up even more.
For the old S9 miner I just took apart full weight: 152 ounces using a postage scale.
Take off the fans, the controller, the fan guards, the other steel bits, 3 ribbon cables, screws and put them in one pile.
Knock off all the heatsinks which are aluminum, and put them on top of the case which is also aluminum. 128 ounces.
Gives me a bit over 84% that can be recycled anywhere.
*The fans were not the ones that came with it, not sure about the fan guards so your numbers might be a bit different.
Any MAJOR farm that can't sell their old equipment on the secondary market because the hardware no longer works is going to have some way to get rid of this stuff.
Remember, there is a monetary value attached to it. Here in NY at the low end you get $0.50 a pound for aluminum, that is me waling in off the street.
If I had more, like I pile all the broken miners from a large operation and strip them. I could probably get 10%+ more if I am bringing in 1000s of pounds.
Now, on the individual scale, yes stuff might nor be recycled, but a commercial operation would never leave that money unclaimed.
-Dave