We include our abrasive papers, anything else that might contain
precious metals, in with our sweeps. The refiners have never
complained, and it’s more cost-effective than waiting until we have
hundreds of sheets to refine ontheir own.
Depending on how you use those sheets, there could well be a lot of
value, but it does depend on the grit, how much you use them, and
whether you use oil or water to lubricate them.
Be aware, though, that you should keep using papers until they are
unusable - my dad binned all of my 3M microfinishing papers because
he thought they looked worn out, when in fact they were just
super-smooth. It cost UKP 30 to replace them, and you can’t buy them
super-smooth - they only go like that after a lot of use.