In cities across the world, there are millions of tons of obsolete cables and pipes. The grounds underneath our cities are like mines. In Sweden, hidden deposits of aluminum, copper and lead have a value of several tens of billions of dollars on the world market.

Cable-X is developing techniques to extract metals from old pipes

Telephone companies and utilities install new communication and power cables everyday, and in many cases, the old wires remain. They are simply too expensive and technically difficult to dig up.

High metal prices and increasingly demanding environmental legislation means that interest is increasing to recover these abandoned metals.

That’s why more and more people are asking whether we should use the land under our feet as a future mine.

To do this, one has to chart the discoveries, develop cost-effective methods for extraction of the metals, and analyze the technical, economic and legal conditions.

“Cities like mines,” a research project at Linköping University, is trying to identify the amount of metal embedded in Swedish urban infrastructure. The emphasis here is on those parts of the systems that are not used. The project also includes developing systems for the extraction of metals and to evaluate technologies from an economic and environmental perspective. “Cities like mines,” is being financed by Vinnova and includes the participation of scientists, the recycling industry and several municipalities.

Urban mining complements mining

“The increasing competition for natural resources means that we want to access the untapped reservoir of material hidden in buildings, in the ground and in landfills,” says Joakim Krook, a lecturer in Environmental Technology at Linköping University and project manager for the “Cities like mines” project.

“We feel that many decision makers in society and the business community are concerned that there will be a shortage of key materials, particularly certain metals. The shortage is caused by a combination of external changes such as increased population, economic and technological growth in developing countries, and the fact that we have already extracted a significant proportion of the metals contained in known deposits,” says Krook.

“A sign of what is happening is the increasing prices for strategic metals. We know that large stores of these substances are hidden in urban infrastructure and buildings. The amount of copper in our buildings and cities around the world is comparable to what remains in the world’s known deposits,” continues Krook.

“So there is a potential to replace traditional mining with “urban mining” – locating metal volumes that are not being used, that are hibernating, so to speak. There are buildings that are not used, electronics and furniture, and buried cables, gas and other metal tubes that are no longer part of our infrastructure,” says Krook.

Precious metals in old industrial parks

As part of the project “Cities like mines,” researchers at Linköping University examined the town of Norrköping. The ground under buildings and roads consist of many different materials that are interesting from a recycling point of view. They include for example:

  • District heating pipes of steel.
  • Water and sewage pipes of copper, iron and steel.
  • Lighting cables containing copper and aluminum.
  • Copper and aluminum in cables for high and low voltage.
  • Telephone cables containing copper.
  • Buried abandoned pipelines made of steel and copper.

The study in Norrköping lasted for a year and was based on a very large amount of data. It included mapping the disconnected wires, tubes, and pipelines; studying digitized maps; analyzing GIS data and other information from the owners of the wires; and historical statistics from the municipality on the technical systems.

The survey showed that for Norrkoping has about 5,000 tons of metal in its disconnected infrastructure systems. “To be specific, we found 4,455 tons of iron in the fully disconnected city gas/heating network, 560 tons of copper in the fully disengaged DC network and the disconnected parts of the AC network, and 27 tons of aluminum in disconnected cables,” says Björn Berglund, researcher at the Environmental Technology department at Linköping University.

A sub-project was to study an old industrial area in the city center. The idea is that Norrköping will modernize the area and convert it into a residential and commercial area. The plans include demolishing all the buildings, remediating the contaminated soil, and recycling the infrastructure that is currently hidden under the surface. Altogether, there are 100 km of buried materials in the area weighing an estimated 300 tons with an economic value close to SEK 5 million.

Should one go out with pick and shovel and start digging? No, it’s not that simple of course, as both the technology and metal prices play a crucial role.

In the case of cleaning up an entire industrial area, traditional technology with exhumation could apply and may be cost effective. How do you recover metals in the cables under buildings and streets? Here it is more difficult and expensive to dig or drill, but there are interesting technologies that open up new possibilities. With the price of copper at SEK 50/kilo, and excavation costs of around SEK 1,000/meter, the development of new recycling methods is in full swing.

New recycling practices

Researchers at Linköping University’s Environmental Technology department have received SEK 3 million from Formas to evaluate different techniques to extract metals from the disconnected infrastructure systems that are buried under cities.

The project, “Economic and environmental evaluation of metal extraction from unplugged network of cities,” is a cooperation between researchers at the Linköping’s Tekniska Verken, Observation Networks AB, Stena Metall AB and Cable-X.

Within the framework of the project, a cheap method to recover the metal core of copper cables is being tested in Linköping.

Here is how it works: An organic and biodegradable solvent is pumped into the copper cable that reduces the friction between the cable and the casing. The copper core can then be pulled out with a winch. The technique was developed by Austrian company Cable X and is being applied in Sweden.

“We see great potential in the possibility of recycling cable cores of copper in an environmentally sound way,” says Rolf Neuendorff, Swedish representative for Cable-X and participant in the research project.

“Old copper pipes are being replaced by high-performance fiber optic cables and the combination of the recovery of copper and the exploitation of the resulting cavity in the cord is very interesting from an economic standpoint. With this technology we can use cables that are up to 300 m long, but it is most common with lengths of around 125 m. The time for extraction of the cable core including preparation depends on the type of cable and takes anywhere from 1.5 to 5 hours.”

The article was published in December 2011