We continue to extract metals from the earth's crust, with the associated risks to people and the environment, although only half of some of the metals we have already extracted are actually used. So, where are these unused metals? In many cases the world of the Urks.

Björn Wallsten, fresh PhD from Linköping University's Division for Environmental Technology and Management, has written the world's first doctoral thesis in Urban Mining, titled The Urk World -- Hibernating Infrastructures & the Quest for Urban Mining. The word 'Urk' is an abbreviation seen on old Swedish infrastructure maps. It stands for 'urkopplad', Swedish for 'disconnected'.

Beneath Swedish cities like Norrköping (population approx. 135,000) and Linköping (population approx. 150,000) there are kilometres of disconnected cables and pipes: decommissioned DC mains, gas lines, disconnected AC mains, heavy-duty electrical cables that served now-defunct mills and factories, remnants of old tram lines, district heating pipes and much more. In Norrköping alone this adds up to at least 5,000 tonnes of iron, copper and aluminium, that is sitting in the ground, unproductive.

The studies conducted by Björn Wallsten show that there are already four or five kilos of disconnected copper per person in the infrastructure of Swedish cities.

But is it worth retrieving these volumes of copper, iron and aluminium?

According to Björn Wallsten's thesis, the answer is clearly no:

Swedish environmental legislation is not designed to handle this type of metal storage. The law is unclear when it comes to 'urks', so in practice they are seen as low-risk environmental waste.

"The responsibility to deal with them doesn't end up on a single party, which means they are low priority and something people just want to forget, if they haven't already done so," says Björn Wallsten.

This will soon be a major problem.

"If we continue to upgrade the Swedish electricity and telecommunications networks while ignoring the copper in the cables, Sweden will soon have as much scrapped and unused copper per person as there is copper in use per person in most developing countries," he explains.

Moreover, copper is an example of a metal of which we have extracted more than half of the known resources in the earth's crust, and where mining continues at a steady pace.

Therefore, in his thesis Björn Wallsten investigated different strategies for extracting the metals we have buried. Firstly, simply digging them up at sites where the concentration is high, for example in older industrial areas. Secondly, removing the decommissioned lines when excavation is underway for maintenance, repairs or when new infrastructure is installed.

But with current legislation, attitudes to resources, low metal prices and existing techniques for excavating recovering metals, neither strategy is directly profitable.

"One disadvantage of recycling during maintenance is that for instance in Linkoping it would take 100 years to recover the 60 per cent of 'urks' that are located close to the operational power grid. But synchronising removal with roadworks is still a move in the right direction. Excavating available 'urks' would reduce carbon emissions emanating from power grid maintenance," he says.

But at the national level, other measures are required.

"We need a whole new approach to how we deal with resources in the community, we need the political will and new regulatory frameworks for a green shift. Hopefully my thesis will help encourage both research and policy to focus on society's use of resources. For example urban mining should be an important area of research in sustainable urban development."

Bjorn Wallsten's thesis, The Urk World -- Hibernating Infrastructures & the Quest for Urban Mining, is part of a larger research project: Resources 2.0 -- Urban and Landfill Mining. Research coordinator is Joakim Krook, assistant professor at Linköping University's Division for Environmental Technology and Management.

Research on urban mining investigates urban areas as mines and resource bases for many different materials.