Not using nanobots, but some municipal waste incineration plants are already recovering valuable metals. A more recent development is using dry discharge of bottom ash to recover >95% of all metals [1].
From 100 000 metric tons of clinker, ZAV Recycling AG in Hinwil (Switzerland) is extracting 60kg of gold, 1500kg of silver and 800 metric tons of copper each year.
From 100 000 metric tons of clinker, ZAV Recycling AG in Hinwil (Switzerland) is extracting 60kg of gold, 1500kg of silver and 800 metric tons of copper each year.
[1] http://www.hz-inova.com/cms/wp-content/uploads/2016/03/04b_R...