Urban Mining of Metals

by Chris Tuppen

Chris Tuppen (British, born 1954) has been involved in sustainability for over twenty years. He runs Advancing Sustainability LLP and is an honorary professor at Keele University. He was previously BT’s chief sustainability officer.

By 2052, for many materials, and especially metals, urban mining will exceed extractive mining. That is to say, it will become more economically attractive to recover and recycle than to dig and refine. This transformation will be driven by a combination of three key factors.First will be the increasing scarcity of some naturally occurring metal ores. Second will be high level of societal stocks for many of the more common elements such as iron and aluminum. And third will be ever-higher processing costs associated with ore refining.


There are several interrelated factors to consider in predicting specific metal ores for which demand may soon exceed supply. The first is natural abundance. For a metal ore to be economically recoverable it needs to occur in a concentrated fashion. Natural abundance, in either the earth’s crust or its oceans, gives a clue to its overall availability, but not the full story. For example, although the world’s oceans host around 15,000 tonnes of dissolved gold10 valued at ~USD 750 billion, it’s in such low concentrations that it’s simply not worth recovering. (At least not yet!)

Second, consider reserves. At any point in time the metals industry has good knowledge about untapped, economically viable, proven reserves and a reasonable estimate of undiscovered resources. Both of these figures continually change as new discoveries are made and existing mines are depleted. Some elements are sufficiently common for scarcity not to be a problem for decades to come. In those cases the total resource is ample and new reserves are likely to be found whenever the old ones are depleted.

Finally, some of the rarer metals are often recovered as a byproduct of other metal extraction. For example, only 30% of new silver is mined directly; the remaining 70% is a by-product of lead, zinc, copper, or gold production. The indium used for LCDs and touchscreens, for instance, all comes from lead and zinc smelters.

Societal Stocks

Over the centuries large quantities of metals have been transferred from underground rock to aboveground products. There are now substantial stocks of metal in manufactured items12—over fourteen billion tonnes of steel and in excess of two hundred million tonnes of copper, to take two examples. Major infrastructure development, especially in the emerging economies, will further increase societal stocks, and when population growth levels off, this will mean larger fractions of primary demand can be provided through recycling.

The recycling rates of many heavily used metals are already high: around 80% for steel, for example. If one assumes that around 4% of societal steel stock reaches the end of its life every year, and that recycling rates remain high, one can predict that urban rather than extractive mining will be the dominant source of new steel before 2020.

Ore Processing Costs

Most metals have to be chemically extracted from their ores using large amounts of energy, often emitting significant quantities of CO2 and other pollutants in the process. The increasing cost of energy and carbon will be reflected in the economics of the metal industry.

The processing of ore also often requires resources from other scarce natural systems, especially the provision of water. For example, even though Chile’s water demand is already six times greater than water renewals, the water consumption of the Chilean mining industry is still expected to increase by 45% by 2020.

Other Influences

But these key factors don’t tell the whole story. The advent of urban mining will also be influenced by geopolitics. Some elements are concentrated in just a few places, and access can be restricted by conflicts and/or trade barriers. For example, the Democratic Republic of the Congo is rich in minerals, but links to human rights abuses has led to campaigns for such minerals to be avoided. From a different perspective, Europe is highly dependent on imports for many crucial metals, and the European Commission, concerned about future availability, has recently highlighted that China produces 95% of all rare earth concentrates, Brazil 90% of all niobium, and South Africa 79% of all rhodium.

The distribution of metal usage also changes as demands change. For example, the introduction of the digital camera has seen a large reduction in the use of silver in conventional photographic film. But this has been more than compensated for by the use of silver in everything from contacts in PV panels to thin fibers in socks to counteract odors.

Efficiency matters, too. Metal stocks will last longer if the amount used per unit of production can be substantially decreased. This has already happened in a number of instances, such as the thickness of metal in beverage cans and the miniaturization of electronic equipment.

When a suitable substitute exists, it extends the reserves of a metal. But the availability of suitable alternatives varies considerably and is dependent on the chemical and physical properties required for any specific application.

Metals to Watch

Taking all these factors into consideration, it is quite straightforward to predict which metals will be in good supply for years to come.

Fortunately these include the industrially critical elements aluminium, iron, silicon, and titanium. Metals frequently listed on “endangered” lists include indium, silver, and some of the rare earths.

Indium is inherently scarce; estimates place its economically viable proven reserves at around 11,000 tonnes, which represents a fifteen years’ supply at current consumption rates.17 Even the most optimistic estimate of predicted global resources comes out at a mere 50,000 tonnes. Over the past fifteen years indium production has increased more than tenfold. This has been due to its increasing use in optically active compound semiconductors and the use of indium tin oxide as a transparent electrical conductor across the front of computer, smartphone, and TV screens as well as thin-film solar panels. Fortunately these applications require only small amounts per unit of production, with a typical screen needing only around 50 mg of indium.

The downside of this frugalness is that societal stocks of indium are highly dispersed, making recovery for reuse very difficult. As the prices of screens and PV panels continue to fall, and demand thereby increases, it will be increasingly difficult to supply—and recycle—sufficient indium. There are prospects of carbon nanotubes offering a substitute for transparent conductive films, but this could be a long way off.

Silver has economically viable proven reserves of around 500,000 tonnes,20 representing seventeen years of current consumption. It is widely used in industrial applications as well as for jewelery, silver plate, and coins. Some uses are growing very rapidly; in particular the solar industry has emerged as a significant industrial user. Silver demand for this sector grew 30% in 2009 and is expected to show a further tenfold increase over the next several years.

The rare earths neodymium, dysprosium, and terbium are all used to make strong, lightweight magnets that are particularly effective in wind turbines and electric cars. The rare earths (also known as the lanthanides) are notoriously difficult to separate from each other.

From a natural abundance perspective they are not that rare. However, viable sources are scarce. China not only hosts the biggest reserves of usable rare earth ore but completely dominates its processing.

Based on proven and projected reserves, projected consumption levels, and current recycling rates, indium, silver, dysprosium, and quite a few more metals could well have “run out” by 2052. Some will undoubtedly be “saved” by technological developments and substitutions, while shortages of others will prompt greater recovery and recycling to take place.

Ultimately this analysis leads me to conclude that over the next forty years there will be major increases in urban mining—in some cases because reserves are no longer available, and in others because large societal stocks will make it more financially attractive to recover and recycle than to dig and refine. So, at least for metals, the dream of circular material flows will eventually happen—but through conventional economic drivers rather than philosophy.