To unlock this you have to manually recycle 100 scrap cubes using a Manticore tug ship.
You can do this in two ways:
1: Poor guy method
* Fly to a scrap cube while piloting a Manticore tug.
* Right click (or F) the scrap cube and select the option to tow it.
* Now tow it to a NPC scrap recycling station, fly above the "drop point" and press F to release the cube.
This will litterally take days to do, as scrap processors are located far from the scrap fields and travel speed is very limited while towing a cube. It's not impossible but would probably challenge your patience. Skip this method and wait until you are rich.
2: Rich guy method
* Build a scrap processing station in a system that contain scrap. Windfall 4, for example.
* Build 10 scrap processors to speed this up as they have a long cooldown between accepting a cube.
* Set the station to only accept scrap from your faction. (trade rules)
* Build several Manticore tugs. I bought 50.
* Assign all manticore tugs to salvage for the station.
* Now keep an eye on the ships. Before they return their scrap to the station, select them (grouped or 1-by-1) and fly them to a location close to the station.
* Now teleport to the ships one at a time and unload their cargo in the scrap processors.
Note: Any automatic return of scrap to the station does not count. You must deposit 100 scrap cubes manually to unlock the achievement.
Note 2: The amount you have returned is tracked in player statistics as "objects recycled". When it reaches 100, the achievement unlocks.