In this page you can find a detailed description for unlocking "Reduce, Reuse, Recycle" achievement in Prey. You get this achievement by recycling at least 20 objects at the same time. You can do this by using one of the gadgets called Recycler Charger.
Warning - You won't get this achievement if you throw 20 objects into a big "stationary" Recycler!
This achievement can be done at any moment after you get one of the Recycler Charges - presented in the picture above. Those charges can be found in various places in the station (in the later parts of the game you can even craft them yourself). You can find them in, e.g. Volunteer Quarters in Neuromod Division or in the safe in Security Office in Talos I Lobby.
When you get one of the charges you should save the game (you don't want to lose any valuable items!) and be sure that you have at least 20 different items in your inventory (besides junk you can also use, e.g. weapons, ammo or food). Start dropping them one by one so they can all lay on the ground next to where the protagonist is (you can see it in the picture 1). Take a few steps back and throw the Recycler Charge at the items. When the charge explodes all items are sucked in (picture 2) and converted into materials. At the same time you, for your efforts, get the achievement.