If you want to buy
paper doily, please
contact us.
INTRODUCTION
Recycling, collection, processing, and reuse of materials that would
otherwise be thrown away. Materials ranging from precious metals to
broken glass, from old newspapers to plastic spoons, can be recycled.
The recycling process reclaims the original material and uses it in new
products.
In general, using recycled materials to make new products costs less and
requires less energy than using new materials. Recycling can also reduce
pollution, either by reducing the demand for high-pollution alternatives
or by minimizing the amount of pollution produced during the
manufacturing process. Recycling decreases the amount of land needed for
trash dumps by reducing the volume of discarded waste.
Recycling can be done internally (within a company) or externally (after
a product is sold and used). In the paper industry, for example,
internal recycling occurs when leftover stock and trimmings are salvaged
to help make more new product. Since the recovered material never left
the manufacturing plant, the final product is said to contain
preconsumer waste. External recycling occurs when materials used by the
customer are returned for processing into new products. Materials ready
to be recycled in this manner, such as empty beverage containers, are
called postconsumer waste.
YPES OF MATERIALS RECYCLED Just about any material can be recycled. On
an industrial scale, the most commonly recycled materials are those that
are used in large quantities-metals such as steel and aluminum,
plastics, paper, glass, and certain chemicals.
Steel There are two methods of making steel using recycled material: the
basic oxygen furnace (BOF) method and the electric arc furnace (EAF)
method. The BOF method involves mixing molten scrap steel in a furnace
with new steel. About 28 percent of the new product is recycled steel.
Steel made by the BOF method typically is used to make sheet-steel
products like cans, automobiles, and appliances. The EAF method normally
uses 100 percent recycled steel. Scrap steel is placed in a furnace and
melted by electricity that arcs between two carbon electrodes. Limestone
and other materials are added to the molten steel to remove impurities.
Steel produced by the EAF method usually is formed into beams,
reinforcing bars, and thick plate.
Approximately 68 percent of all steel is recycled, making it one of the
world's most recycled materials. In 1994 37 billion steel cans, weighing
2,408,478 metric tons (2,654,892 U.S. tons), were used in the United
States, of which 53 percent were recycled. In 1995 more than 60 million
metric tons (70 million U.S. tons) of scrap steel were recycled in the
United States.
Aluminum Recycling aluminum in the United States provides a stable,
domestic aluminum supply amounting to approximately one-third of the
industry's requirement. In contrast, most of the ore required to produce
new aluminum must be imported from Jamaica, Australia, Surinam, Guyana,
and Guinea. About 2 kg (about 4 lb) of ore, a mixture of aluminum oxides
called bauxite, are needed to make 0.5 kg (1 lb) of aluminum.
The U.S. aluminum industry has recognized the advantage of a domestic
aluminum supply and has established systems for collection,
transportation, and processing. For this reason, aluminum cans almost
always produce a profit in community recycling programs. A number of
states require deposits for beverage containers and have established
redemption centers at supermarkets. The overall recycling rate of all
forms of aluminum is about 35 percent.
Cans brought to collection centers are crushed, baled, and shipped to
regional mills or reclamation plants. The cans are then shredded to
reduce volume and heated to remove coatings and moisture. Next, they are
put into a furnace, melted, and formed into ingots, or bars, weighing
10,000 kg (30,000 lb) or more. The ingots go to another mill to be
rolled into sheets. The sheets are sent to a container plant and cut
into disks from which new cans are formed. The cans are printed with the
beverage makers' logos and are shipped (with tops separate) to the
filling plant.
About 100 billion aluminum beverage cans are used each year in the
United States and about 65 percent of these are then recycled. The
average aluminum can in the United States contains 40 percent
postconsumer recycled aluminum. About 97 percent of all soft drink cans
and 99 percent of all beer cans are made of aluminum.
Plastics Plastics are more difficult to recycle than metal, paper, or
glass. One problem is that any of seven categories of plastics can be
used for containers alone. For effective recycling, the different types
cannot be mixed. Most states require that plastic containers have
identification codes so they can be more easily identified and
separated. The code assigns a particular number to each of the seven
plastics used in packaging. The number 1 refers to polyethylene
teraphthalate (PET) and the number 2 refers to high-density polyethylene
(HDPE). PET can be made into carpet, or fiberfill for ski jackets and
clothing. HDPE can be recycled into construction fencing, landfill
liners, and a variety of other products. Plastics coded with the number
6 are polystyrene (PS), which can be recycled into cafeteria trays,
combs, and other items.
The recycling process for plastic normally involves cleaning it,
shredding it into flakes, then melting the flakes into pellets. The
pellets are melted into a final product. Some products work best with
only a small percentage of recycled content. Other products, such as
HDPE plastic milk cases, can be made successfully with 100 percent
recycled content. The plastic container industry has concentrated on
weight reduction and source reduction. For example, the one-gallon HDPE
milk container that weighed about 120 gm (about 4.2 oz) in the 1960s
weighed just 65 gm (about 2.3 oz) in 1996.
In the United States, the overall recycling of plastic was under 4.7
percent in 1994, with the recycling rate of plastic containers at about
19 percent. Most discarded plastic is in the form of plastic containers.
Plastics made up about 9 percent of the waste stream by weight in 1995.
Paper and Paper Products Paper products that can be recycled include
cardboard containers, wrapping paper, and office paper. The most
commonly recycled paper product is newsprint.
In newspaper recycling, old newspapers are collected and searched for
contaminants such as plastic bags and aluminum foil. The paper goes to a
processing plant where it is mixed with hot water and turned into pulp
in a machine that works much like a big kitchen blender. The pulp is
screened and filtered to remove smaller contaminants. The pulp then goes
to a large vat where the ink separates from the paper fibers and floats
to the surface. The ink is skimmed off, dried and reused as ink or
burned as boiler fuel. The cleaned pulp is mixed with new wood fibers to
be made into paper again.
Paper and paper products such as corrugated board constitute about 40
percent of the discards in the United States, making it the most
plentiful single item in landfills. Experts estimate the average office
worker generates about 7 kg (about 15 lb) of wastepaper (about 1,500
sheets) per month. Every ton of paper that is recycled saves about 1.4
cu m (about 50 cu ft) of landfill space. One ton of recycled paper saves
17 pulpwood trees (trees used to produce paper).
Glass Scrap glass taken from the glass manufacturing process, called
cullet, has been internally recycled for years. The scrap glass is
economical to use as a raw material because it melts at lower
temperatures than other raw materials, thus saving fuel and operating
costs.
Glass that is to be recycled must be relatively free from impurities and
sorted by color. Glass containers are the most commonly recycled form of
glass, and their colors are flint (clear), amber (brown), and green.
Other glass, such as window glass, pottery, and cooking utensils, are
considered contaminants because they have different compositions than
glass used in containers. The recycled glass is melted in a furnace and
formed into new products.
Glass containers make up 90 percent of the total glass used in the
United States. The 1994 recycling rate for glass was about 33 percent.
Other uses for recycled glass include glass art and decorative tiles.
Cullet mixed with asphalt forms a paving material called glassphalt.
For the paper doily
prices
do not hesitate to
contact us.