Asked by: John Loader, Leyburn
A growing number of firms believe that landfill mining could soon be economically viable. The idea is to plunder waste sites for resources like precious metals from discarded electronic equipment. Circuit boards contain small amounts of copper, tin and even gold. It turns out that a tonne of electronic waste contains as much gold as 17 tonnes of ore.
It's hard to say definitively when landfill mining will become a truly commercial proposition. First, we need to crack the technology for efficiently harvesting valuable materials from waste. Various magnetic techniques already exist for removing ferrous - and even non-ferrous metals. But a US aluminium company called Alcoa is working on a method called fractional crystallisation for separating alloys from each other. I'd love to tell you how it works, but Alcoa owns the technology and isn't giving anything anyway.
Get more fascinating Q&As from BBC Focus magazine by following @sciencefocusQA