A great article about HP's closed loop for used HP cartridges.
The technical details are:
Customer returning the empty cartridges to HP using a Freepost bag or label. Not any cartridges are accepted, they must be HP brand.
When the cartridges arrive they are put through a machine that de-bags them, then they are passed along a conveyor belt to the x-ray machine that quickly sorts the cartridges into family types
From there the cartridges are passed to a shredder which shreds all the cartridges into small pieces, they are then passed through a separator that separates the metals from the plastics.
The cartridges have now become a raw material, the plastics are mixed with other PET plastics, usually from recycled water bottles and made back into HP ink cartridges.
New HP cartridges have between 50 and 70% recycled material.
The article goes on to express concerns about HP's focus on shredding and recycling rather than reuse. This is a really good point, and worth further thought. How might cartridges be reused whilst maintaining protection against counterfeits?