As commodity prices boom, old waste dumps are being mined for their metals
For decades, electrical equipment which no longer had any functional value, was placed in waste landfills without a thought for their metal value. Since 2000, the market price for raw copper has fluctuated greatly. Suddenly, it was economically worthwhile to mine the landfills for this hidden treasure. Countries like Switzerland and Germany, with good records of the placement of special wastes in their underground waste disposal sites, were in a position to cost-effectively recover these metals from hazardous waste.
The practice of landfill mining does not come without risks. Fluctuations in the commodity price makes long-term planning and investment in safety infrastructure risky. Umwelt.Science looks at the case of transformers, which contain polychlorinated biphenyls, a group of compounds which are classed as toxic by the Stockholm Convention, and banned under European, German and Swiss law. How is the excavation and recycling of transformers managed?
Urban mining, or landfill mining, is a field which is dependent on the economic value of materials. It has traditionally been cheaper to import raw material from mines than to recover it from waste in a landfill. The first time a waste landfill was excavated in Europe was in 1990 (Spitzau Landfill, Vienna). Germany conducted a pilot demonstration project at Burghof/Horrheim Deponie, in 1993-4. Since then, several thousand tonnes of waste have been excavated from German landfills. The main reasons have been for environmental safety, such as water table protection, or for reassignment of land use. In only 13% of the cases1, was the operation specifically to recover materials for recycling.
From an environmental perspective, it would seem logical to reutilise materials as much as possible, preserving the environment from the impacts of mining, and the depletion of resources. Examples of recovery of heavy metals from hazardous waste landfills are: nickel and vanadium from heavy oil, selenium from mercury-selenium slurry, tellurium from concentrates from non-ferrous industries, and copper from PCB-containing transformers. Copper is less present in landfills than other metals, such as iron, but has a much higher market value. Overall, copper provides twice the revenue as iron in landfill mining operations.
Polychlorinated biphenyls (PCBs) are a group of organochlorine compounds once commonly used in a broad range of industrial applications, including as dielectric fluids and coolants in electrical devices, such as transformers, motors, and capacitors. These compounds vary in the number and placement of chlorine atoms, and consequently their properties, such as solubility and environmental persistence, but what they all have in common is that they are highly toxic and carcinogenic. They are all persistent in ecosystems, and bioaccumulate, their concentrations in organisms increasing the further up the foodchain, from fish and birds to humans. As a result, they are regulated by the Stockholm Convention on POCs (persistent organic compounds) (2001), and bans exist worldwide on their manufacture, use, transport and storage. They must be disposed of as hazardous waste.2
Throughout the 1980s and 1990s, despite the bans, there have been many incidents and accidental releases, leading to widespread contaminations of the air, water and ground, with incalculable cost to human and environmental health. Since these compounds are persistent, so too are the health effects. One can only hope that this earlier careless and blasé attitude towards the hazards of organochlorines like PCBs is less persistent.
Now, the recent interest in urban mining for the economic recovery of landfilled materials opens up a new avenue for locked away PCBs and other POCs to return to the surface. The manufacturing and use sectors may have learnt to deal with the dangers correctly, through the force of law. Recycling, however, may be done by different industry sectors.
The transformers are removed from their underground landfill (Class IV), and brought to the surface, where they are shipped to a recycling firm. Here, they are opened, the PCB-containing liquid contents flushed out, and the metal cleaned and shredded, before being returned to the material market. The metals recovered include copper, aluminium and soft iron.
The construction, authorisation and operation of a Landfill Class IV is regulated at the European level by EUR directive 2003/33/EG. In Germany, this is applied through the Landfill Ordinance. Where a methodical system of traceability has been maintained, as is the case by the underground depositories in Bad Hersfeld and Zielitz bei Magdeburg (operated by K+S KALI GmbH), materials may be recovered selectively. In these deposits, the wastes were stored by type, and any possibility of contact with air and groundwater excluded. Careful documentation ensures that the wastes may be found and recovered, even after many years. 3
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