Landfill mining
Encyclopedia
Landfill mining and reclamation (LFMR) is a process whereby solid waste
s
which have previously been landfill
ed are excavated and processed. The function of landfill mining is to reduce the amount of landfill mass encapsulated within the closed landfill and/or temporarily remove hazardous material to allow protective measures to be taken before the landfill mass is replaced. In the process, mining recovers valuable recyclable materials, a combustible fraction, soil, and landfill space. The aeration of the landfill soil is a secondary benefit regarding the landfill's future use. The combustible fraction is useful for the generation of power. The overall appearance of the landfill mining procedure is a sequence of processing machines laid out in a functional conveyor system. The operating principle is to excavate, sieve and sort the landfill material.
The concept of landfill mining was introduced as early as 1953 at the Hiriya
landfill operated by the Dan Region Authority next to the city of Tel Aviv
, Israel
. Waste contains many resources with high value, the most notable of which are non-ferrous metals such as aluminium cans and scrap metal
. The concentration of aluminium in many landfills is higher than the concentration of aluminum in bauxite
from which the metal is derived.
and other substances then refilled with wastes requiring disposal.
Mining construction landfill sites is the simplest form of landfill mining. Construction landfills contain three basic components, wood, scrap metal and gypsum, or drywall, along with a minimal amount of other construction materials. The wood collected can be used as fuel in coal burning power plants and the scrap metal reprocessed.
Mining of municipal landfills is more complicated and has to be based on the expected content of the landfill. Older landfills, in the United States before 1994, were often capped and closed, essentially entombing the waste. This can be beneficial for waste recovery. It can also create a higher risk for toxic waste
and leachate
exposure as the landfill has not fully processed the stewing wastes. Mining of bioreactor landfill
s and properly stabilized modern sanitary landfills provides its own benefits. The biodegradable wastes are more easily sieved out, leaving the non-biodegradable materials readily accessible. The quality of these materials for recycling and reprocessing purposes is not as high as initially recycled materials, however materials such as aluminum and steel are usually excluded from this.
Landfill mining is most useful as a method to remediate hazardous landfills. Landfills that were established before landfill liner
technology was well established often leak their unprocessed leachate into underlying aquifers. This is both an environmental hazard and also a legal liability. In the US, Environmental Protection Agency
fines can tax the local economy up to 30 years after the site has closed. Mining the landfill simply to lay a safe liner is a last, but sometimes necessary resort.
or front end loader
uncovers the landfilled materials and places them on a moving floor conveyor belt to be taken to the sorting machinery. A trommel
is used to separate materials by size. First, a large trommel separates materials like appliances and fabrics. A smaller trommel then allows the biodegraded soil fraction to pass through leaving non-biodegradable, recyclable materials on the screen to be collected.
An electromagnet is used to remove the ferrous
material from the waste mass as it passes along the conveyor belt.
A front end loader
is used to move sorted materials to trucks for further processing.
Odour control sprayers are wheeled tractors with a cab and movable spray arm mounted on a rotating platform. A large reservoir tank mounted behind the cab holds neutralising agents, usually in liquid form, to reduce the smell of exposed wastes.
which separates light organic material from heavy organic material. The separate streams are then loaded, by front end loaders, onto trucks either for further processing or for sale. Further manual processing can be done on site if processing facilities are too far away to justify the transportation costs.
Waste
Waste is unwanted or useless materials. In biology, waste is any of the many unwanted substances or toxins that are expelled from living organisms, metabolic waste; such as urea, sweat or feces. Litter is waste which has been disposed of improperly...
s
which have previously been landfill
Landfill
A landfill site , is a site for the disposal of waste materials by burial and is the oldest form of waste treatment...
ed are excavated and processed. The function of landfill mining is to reduce the amount of landfill mass encapsulated within the closed landfill and/or temporarily remove hazardous material to allow protective measures to be taken before the landfill mass is replaced. In the process, mining recovers valuable recyclable materials, a combustible fraction, soil, and landfill space. The aeration of the landfill soil is a secondary benefit regarding the landfill's future use. The combustible fraction is useful for the generation of power. The overall appearance of the landfill mining procedure is a sequence of processing machines laid out in a functional conveyor system. The operating principle is to excavate, sieve and sort the landfill material.
The concept of landfill mining was introduced as early as 1953 at the Hiriya
Hiriya
Hiriya is a former waste dump located southeast of Tel Aviv, Israel.-History:Hiriya takes its name from the pre-1948 Arab village of al-Khayriyya, which was built on the site of the ancient biblical town of Beneberak....
landfill operated by the Dan Region Authority next to the city of Tel Aviv
Tel Aviv
Tel Aviv , officially Tel Aviv-Yafo , is the second most populous city in Israel, with a population of 404,400 on a land area of . The city is located on the Israeli Mediterranean coastline in west-central Israel. It is the largest and most populous city in the metropolitan area of Gush Dan, with...
, Israel
Israel
The State of Israel is a parliamentary republic located in the Middle East, along the eastern shore of the Mediterranean Sea...
. Waste contains many resources with high value, the most notable of which are non-ferrous metals such as aluminium cans and scrap metal
Scrap Metal
Scrap Metal were a band from Broome, Western Australia who played rock music with elements of country and reggae. The members had Aboriginal, Irish, Filipino, French, Chinese, Scottish, Indonesian and Japanese heritage. The band toured nationally as part of the Bran Nue Dae musical and with...
. The concentration of aluminium in many landfills is higher than the concentration of aluminum in bauxite
Bauxite
Bauxite is an aluminium ore and is the main source of aluminium. This form of rock consists mostly of the minerals gibbsite Al3, boehmite γ-AlO, and diaspore α-AlO, in a mixture with the two iron oxides goethite and hematite, the clay mineral kaolinite, and small amounts of anatase TiO2...
from which the metal is derived.
Practical applications
Landfill mining is also possible in countries where land is not available for new landfill sites. In this instance landfill space can be reclaimed by the extraction of biodegradable wasteBiodegradable waste
Biodegradable waste is a type of waste, typically originating from plant or animal sources, which may be degraded by other living organisms. Waste that cannot be broken down by other living organisms are called non-biodegradable....
and other substances then refilled with wastes requiring disposal.
Mining construction landfill sites is the simplest form of landfill mining. Construction landfills contain three basic components, wood, scrap metal and gypsum, or drywall, along with a minimal amount of other construction materials. The wood collected can be used as fuel in coal burning power plants and the scrap metal reprocessed.
Mining of municipal landfills is more complicated and has to be based on the expected content of the landfill. Older landfills, in the United States before 1994, were often capped and closed, essentially entombing the waste. This can be beneficial for waste recovery. It can also create a higher risk for toxic waste
Toxic waste
Toxic waste is waste material that can cause death or injury to living creatures. It spreads quite easily and can contaminate lakes and rivers. The term is often used interchangeably with “hazardous waste”, or discarded material that can pose a long-term risk to health or environment.Toxic waste...
and leachate
Leachate
Leachate is any liquid that, in passing through matter, extracts solutes, suspended solids or any other component of the material through which it has passed....
exposure as the landfill has not fully processed the stewing wastes. Mining of bioreactor landfill
Bioreactor landfill
Landfills are the primary method of waste disposal in many parts of the world, including United States and Canada. Bioreactor landfills are expected to reduce the amount of and costs associated with management of leachate, to increase the rate of production of methane for commercial purposes and...
s and properly stabilized modern sanitary landfills provides its own benefits. The biodegradable wastes are more easily sieved out, leaving the non-biodegradable materials readily accessible. The quality of these materials for recycling and reprocessing purposes is not as high as initially recycled materials, however materials such as aluminum and steel are usually excluded from this.
Landfill mining is most useful as a method to remediate hazardous landfills. Landfills that were established before landfill liner
Landfill liner
A landfill liner, or composite landfill liner, is intended to be a low permeable barrier, which is laid down under engineered landfill sites...
technology was well established often leak their unprocessed leachate into underlying aquifers. This is both an environmental hazard and also a legal liability. In the US, Environmental Protection Agency
United States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
fines can tax the local economy up to 30 years after the site has closed. Mining the landfill simply to lay a safe liner is a last, but sometimes necessary resort.
Tools and machinery
The parts of the mining process are the different mining machines. Depending on the complexity of the process more or fewer machines can be used. Machinery is easily transported on trucks from site to site, mounted on trailers. The following machines are added in order in increase of mining complexity:- Excavators
- Moving floor and elevator conveyor belts
- A coarse rotating trommelTrommelA trommel is a screened cylinder used to separate materials by size - for example, separating the biodegradable fraction of mixed municipal waste or separating different sizes of crushed stone....
screen - A fine rotating trommel screen
- A magnet
- Front end loader
- Odor control sprayer
The mechanics of mining
An excavatorExcavator
Excavators are heavy construction equipment consisting of a boom, stick, bucket and cab on a rotating platform . The house sits atop an undercarriage with tracks or wheels. A cable-operated excavator uses winches and steel ropes to accomplish the movements. They are a natural progression from the...
or front end loader
Loader (equipment)
A loader is a heavy equipment machine often used in construction, primarily used to load material into or onto another type of machinery .-Heavy equipment front loaders:A loader A loader is a heavy equipment machine often used in construction, primarily used to load material (such as asphalt,...
uncovers the landfilled materials and places them on a moving floor conveyor belt to be taken to the sorting machinery. A trommel
Trommel
A trommel is a screened cylinder used to separate materials by size - for example, separating the biodegradable fraction of mixed municipal waste or separating different sizes of crushed stone....
is used to separate materials by size. First, a large trommel separates materials like appliances and fabrics. A smaller trommel then allows the biodegraded soil fraction to pass through leaving non-biodegradable, recyclable materials on the screen to be collected.
An electromagnet is used to remove the ferrous
Ferrous
Ferrous , in chemistry, indicates a divalent iron compound , as opposed to ferric, which indicates a trivalent iron compound ....
material from the waste mass as it passes along the conveyor belt.
A front end loader
Loader (equipment)
A loader is a heavy equipment machine often used in construction, primarily used to load material into or onto another type of machinery .-Heavy equipment front loaders:A loader A loader is a heavy equipment machine often used in construction, primarily used to load material (such as asphalt,...
is used to move sorted materials to trucks for further processing.
Odour control sprayers are wheeled tractors with a cab and movable spray arm mounted on a rotating platform. A large reservoir tank mounted behind the cab holds neutralising agents, usually in liquid form, to reduce the smell of exposed wastes.
Operational flow
Excavators dig up waste mass and transport it, with the help of front end loaders, onto elevator and moving floor conveyor belts. The conveyor belts empty into a coarse, rotating trommel. The large holes in the screen allow most wastes to pass through, leaving behind the over-sized, non-processable materials. The over-sized wastes are removed from inside the screen. The coarse trommel empties into the fine rotating trommel. The fine rotating trommel allows the soil fraction to pass through, leaving mid-sized, non-biodegradable, mostly recyclable materials. The materials are removed from the screen. These materials are put on a second conveyor belt where an electromagnet removes any ferromagnetic debris. Depending on the level of resource recovery, material can be put through an air classifierAir classifier
An air classifier is an industrial machine which sorts materials by a combination of size, shape, and density. It works by injecting the material stream to be sorted into a chamber which contains a column of rising air...
which separates light organic material from heavy organic material. The separate streams are then loaded, by front end loaders, onto trucks either for further processing or for sale. Further manual processing can be done on site if processing facilities are too far away to justify the transportation costs.