Americans tossed 292.4 million tons of trash into landfills in 2018, or about 5 pounds of garbage per person per day. Once in a landfill, much of that trash undergoes some wild chemistry, often polluting the surrounding area. But amid all the stinking refuse is potentially valuable material, and some environmentalists and engineers see landfills as a resource to be tapped.
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Landfill mining is the process of uncapping a landfill and sifting through its cells of garbage to reclaim any sort of e-waste, heavy metals, or other recoverable materials that can then be returned to manufacturers and recycled into new products. It sounds promising, but landfill mining has yet to take off widely. I asked some environmental scientists to explain why.
Travis P. Wagner
Professor Emeritus of Environmental Science and Policy, University of Southern Maine and co-author of “Landfill mining: Case study of a successful metals recovery project,” published in the journal Waste Management
There are millions of tons (and billions of dollars in value) of recoverable metals, plastics, and other materials currently stored in landfills. The simple reason mining does not occur is economics: for multiple reasons, the costs to mine a solid waste landfill are currently greater than the value of recoverable materials.
The cost of any mining operation includes extraction of the target ore, processing to concentrate the ore (beneficiation), managing the associated wastes, transporting and selling the material, and finally closing and reclaiming the mine. These costs must be lower than the revenues made from selling the mined material. While the mining of solid waste landfills has many environmental benefits, it is subject to the same economic conditions as traditional mining.
At a typical solid waste landfill, there is inadequate knowledge as to what, where, and how much target material is there. This makes assessing the cost to mine and the potential revenues very difficult. Landfills also present an additional cost: not knowing how much and what types of hazardous materials are present and where they are located. Their presence raises serious worker safety and environmental risks.
Processing landfilled waste to concentrate the material is perhaps the highest cost. For example, with metals, the typical concentration of metal in solid waste is about 5 percent. The other 95 percent of trash has to be temporarily removed and subsequently moved back into the landfill. And, many metals are not isolated but are part of a multi-material article. The cost to remove all the non-metal components can exceed the market value of the steel.
Finally, because of the significant environmental risks in mining a landfill, a landfill mining operation would be permitted only if there were sufficient contingency funds (or insurance). Sufficient funds would be required prior to the start of mining that would ensure the mining operator could cover the costs to properly close and reclaim the mined landfill and to remediate any environmental impacts.
Lúcia Helena da Silva Maciel Xavier
Senior Researcher at the Center for Mineral Technology in Rio De Janiero and co-author of “A comprehensive review of urban mining and the value recovery from e-waste materials,” published in Resources, Conservation and Recycling
First, it is important to differentiate between urban mining and landfill mining. Urban mining is defined as the set of processes for the material obtained from secondary resources. Mostly from waste or post-consumer products. Mining from landfills is one of the possibilities of urban mining.
Mining from landfills presents some limiting aspects, such as the content of organic material that can ‘contaminate’ recoverable materials and also the diversity of materials that turns it difficult to identify and classify materials. Analogously, to the mining of low-grade deposits, which are economically unfeasible.
Finally, urban mining tends to gain space in new business models by the segregation of secondary resources at the source, such as from the selective collection and the carrying out of specific campaigns (e.g. e-waste, metal fractions). However, the main motivation for urban mining lies in the need to obtain materials classified as critical and available with frequency and quantity in secondary resources. For example, we have platinum in automotive catalysts, gold in printed circuit boards, and copper in wires and cables.
Jeff Murray
Vice President and Landfill Practice Leader at HDR
I recently helped facilitate a public open house for a proposed expansion of a lined landfill requiring mining of a closed but unlined legacy landfill. While most attendees understood the need and appreciated the care the community took to remove a liability and provide disposal capacity, there were a couple of residents who were insistent that if a portion of the landfill could be mined, why not mine the entire site and move the landfill to another part of the county? Their motivation was not recovery of recyclable materials or remediation, but righting a perceived wrong when the property was established as a landfill site over 40 years ago.
This story showcases one of the issues facing landfill mining in the United States. In Europe, where they view landfills more negatively, they’ve been mining old landfill sites for decades. So why isn’t it more popular here? In simple terms, we have a separate set of motivations. Energy costs are still comparatively low because of the availability of fossil fuels and natural gas, so we don’t value the energy potential of waste buried in landfills. There is not a strong appetite for energy from waste in many locations that could benefit from the energy value of buried plastics and undegraded organic material. Landfill mining is expensive relative to the cost of developing a new landfill site or just transporting waste to a regional disposal facility in someone else’s backyard. The costs for excavation, physical screening, and managing odors and liquids can be significant barriers.
The recycling market demand for steel, aluminum, or precious metals is not high enough in most instances to offset the costs of mining and cleaning. Americans have been separating valuable plastic and metals from the waste stream poorly for decades, despite long-running education efforts. Our waste could contain valuable material, but once in the ground, that value proposition is significantly lower. Environmental, social and governance pressure is ramping up but isn’t as mature as in other parts of the world. ESG will certainly affect our transition to a more circular and sustainable economy, but it likely won’t initiate widespread landfill mining and reclamation activities. Greenhouse gas emission reduction is not a strong motivator as well. Much of the degradation of organic materials from old landfills occurred in the first decade or two following disposal. Unless the mined waste is less than 10 years old (then why did you bury it in the first place?), the net greenhouse gas reductions after considering the equipment and fuel required may be de minimis.
The popularity of landfill mining may increase over time, with some shifts in the factors above. In the meantime, we’ll continue to monitor Europe and Asia as they explore cost-effective methods. My 25 years of experience in landfills as a solid waste consulting engineer indicates that landfill mining is an intriguing proposition. But will it become a sizable portion of my practice in the next 15 years? Let’s just say I am not pinching my nose or holding my breath.
