There are a few different companies (1, 2, 3, 4, 5, …) working on a few different techniques, methods, and technologies to capture and clean the space junk orbiting around the earth.
There is, however, one thing in common in all of them, and that’s the fact that they are all looking to de-orbit the space junk by either burning it through the atmosphere or if too big, letting it hit the earth in unpopulated areas.
Here I suggest another option to consider that I couldn’t find in any of these projects ( LMK if there is a project that I missed ).
In short, we don’t need to send them back to earth, we can create a repository of them in orbit, like an island of compact space junk, glued together (or a few of them if needed, based on their orbital properties), which should be much cheaper, and easier to do as it takes a lot of energy to de-orbit them all. it also makes it easier to make reusable machines to do it rather than one-use machines that will burn with the debris they are collecting and directing towards the earth.
Later, once we have the inevitable technology in place for in-orbit manufacturing, we can use the piles of valuable, raw material to build other stuff, in-orbit, rather than re-mining and re-sending them back again from the earth, moon, or asteroids.
We can also (and perhaps much easier) use them as fuel for different kinds of propulsion where matter is needed, and it doesn’t matter what kind of matter, just matter, preferably massive matter!
In simple words, we can accelerate particles, ions, atoms, and molecules of the space junk we collected and use them as a very cheap and effective source of propulsion for long space travels.
Another possible use case could be to accelerate them enough and use them to impact an approaching rock early enough to change its trajectory…