Mining landfill Soil
Landfill soil mining and reclamation (LFMR) is a process whereby
solid wastes which have previously been landfilled 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 regrading 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.
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 waste 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 landfills 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.
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 trommel screen
* A fine rotating trommel screen
* A magnet
* Front end loader
* Odor control sprayer
The mechanics of mining
An excavator 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.
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 metal debris.
Depending on the level of resource recovery, material can be put
through an air classifier 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.
From http://en.wikipedia.org/
