Yeah. A lot of plastics are 100 percent recyclable. Eventually you just mine the landfill if it is worthwhile. No? Destroying the plastic seems a waste.
Possible selection and confirmation bias as I design plastic products.
A ton of them are recyclable in their pure state, but I get the impression that a lot of seemingly mundane plastic products these days are actually surprisingly complicated mixes/composite materials: I know something simple like a potato chip bag is at least a 3-layer composite structure, and you've got inks from the label, metal from the barrier layer, polypropylene from the film, and polyethylene from the adhesive layer.
On top of that, the polypropylene film itself is likely a multilayer structure of different copolymers and crystallinities, and it all turns a crappy little thing like a chip bag in to something damn hard to recycle.
Yeah, we already mine tailings from old mines, since the old mining processes were less efficient, and those tailings are now considered economically recoverable ores.
There is another fungus which is capable of turning cellulose from wood into diesel. A fungus which could digest plastic into fuel would be great. http://www.ens-newswire.com/ens/nov2008/2008-11-04-02.asp
Of course this fungus should not be injected into the dump sites. Better dig up the plastic and have it converted into fuel in a chemical plant.