So... issue one: Space junk may be in *about* the same orbit you are... so, your approach speed may not be anything dangerous - walking speed, or maybe that of a car on a freeway. In that case, you can 'snare' the piece of space junk, and stow it until you have an idea of what you'd like to do.
OR... Space junk may be encountered at a relatively high speed - a few hundred miles per hour. Imagine your car having a head-on crash on the freeway - you and the car you hit are moving about 130-150 mph relative to each other... imagine the carnage. What you'd want to do is not lasso or snare it, but somehow capture it - it's *going* to break apart - you may want to catch it in a large net of some kind that can reduce the kinetic energy slow enough that the 'encounter' isn't catastrophic.
OR... Space junk may be moving at many thousands of miles per hour relative to your collector... you'd need to much more massive, and present a firm surface for it to hit - my thought is, a large metallic scoop or funnel - the kinetic energy is going to be released violently - I'm not sure how to avoid it, so you better have a robust vessel of some kind capable of out-lasting the space junk...
Issue Two: You've collected 10 tons of space junk. Now what? You've got to de-orbit this stuff. You need fuel to do it - so, is it moved to a small Progress-type vessel and sent splashing into the sea? How many of these 'de-orbit' vehicles do you carry? When you maneuver, do you maneuver it as well, or do you later rendezvous & transfer the trash for deorbiting?
Issue 3: You have to have a pretty hefty fuel tank because you'll be chasing junk in many orbits - so, you'll be maneuvering quite often. How do you get re-fueled? How often do you get to return home (or, to the space station?) Your mission will cost several million dollars to perform - is there a return on investment...?