Tire recycling - AbsoluteAstronomy.com

Tire recycling or rubber recycling is the process of recycling

Recycling

Recycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...

vehicles tire

Tire

A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...

s (or tyres) that are no longer suitable for use on vehicles due to wear or irreparable damage (such as punctures). These tires are among the largest and most problematic sources of waste

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...

, due to the large volume produced and their durability. Those same characteristics, which make waste tires such a problem, also make them one of the most re-used waste materials, as the rubber

Rubber

Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...

is very resilient and can be reused in other products. Approximately, one tire is discarded per person per year. Tires are also often recycled for use on basketball courts and new shoe products. However, material recovered from waste tires, known as "crumb," is generally only a cheap "filler" material and is rarely used in high volumes.

Tire lifecycle

The tire life cycle can be identified by the following six steps:

Product developments and innovations such as improved compounds and camber tire shaping increase tire life, increments of replacement, consumer safety, and reduce tire waste.
Proper manufacturing and quality of delivery reduces waste at production.
Direct distribution through retailers, reduces inventory time and ensures that the life span and the safety of the products are explained to customers.
Consumers' use and maintenance choices like tire rotation
Tire rotation
Tire rotation or rotating tires is the practice of moving automobile wheels and tires from one position on the car, to another, to ensure even tire wear. Tire wear is uneven for any number of reasons...

affect tire wear and safety of operation.
Manufacturers and retailers set policies on return, re-tread, and replacement to reduce the waste generated from tires and assume responsibility for taking the ‘tire to its grave’ or to its reincarnation.
Recycling tires by developing strategies that combust or process waste into new products, creates viable businesses, and fulfilling public policies.

Landfill disposal

Tires are not desired at landfills, due to their large volumes and 75% void space, which quickly consumes valuable space. Tires can trap methane

Methane

Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...

gases, causing them to become buoyant, or bubble

Landfill gas migration

Landfill gas migration is a complex process of the gas moving from the site of original deposition to other places via diffusion. Usually, the gas moves from areas of high concentration to areas of low gas concentration around a landfill. The process is also affected by the permeability of the...

to the surface. This ‘bubbling’ effect can damage 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...

s that have been installed to help keep landfill contaminants from polluting local surface and ground water. Shredded tires are now being used in landfills, replacing other construction materials, for a lightweight backfill in gas venting systems, 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....

collection systems, and operational liners. Shredded tire material may also be used to cap, close, or daily cover landfill sites. Scrap tires as a backfill and cover material are also more cost-effective, since tires can be shredded on-site instead of hauling in other fill materials.

Stockpiles and illegal dumping

Tire stockpiles create a great health and safety risk. Tire fire

Tire fire

Tire fires, where tires are stored, dumped or processed, exist in two forms: as fast-burning events, leading to almost immediate loss of control, and as slow-burning pyrolysis which can continue for over a decade. They are noted for being difficult to extinguish. Such fires produce a lot of smoke,...

s can occur easily, burning for months, creating substantial pollution in the air and ground. Recycling helps to reduce the number of tires in storage. An additional health risk, tire piles provide harborage for vermin and a breeding ground for mosquitoes that may carry diseases. Illegal dumping of scrap tires pollutes ravines, woods, deserts, and empty lots; which has led many states to pass scrap tire regulations requiring proper management. Tire amnesty day events, in which community members can deposit a limited number of waste tires free of charge, can be funded by state scrap tire programs, helping decrease illegal dumping and improper storage of scrap tires.

Uses

Tires can be recycled into, among other things, the hot melt asphalt

Asphalt

Asphalt or , also known as bitumen, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits, it is a substance classed as a pitch...

, typically as crumb rubber

Crumb rubber

Crumb rubber is a term usually applied to recycled rubber from automotive and truck scrap tires. During the recycling process steel and fluff is removed leaving tire rubber with a granular consistency. Continued processing with a granulator and/or cracker mill, possibly with the aid of cryogenics...

modifier—recycled asphalt pavement (CRM—RAP), and as an aggregate in portland cement

Portland cement

Portland cement is the most common type of cement in general use around the world because it is a basic ingredient of concrete, mortar, stucco and most non-specialty grout...

concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

Tires can also be recycled into other tires.

Pyrolysis

Pyrolysis

Pyrolysis is a thermochemical decomposition of organic material at elevated temperatures without the participation of oxygen. It involves the simultaneous change of chemical composition and physical phase, and is irreversible...

can be used to reprocess the tires into fuel gas

Fuel gas

Fuel gas can refer to any of several gases burned to produce thermal energy.Natural gas is the most common fuel gas, but others include:* Coal gas or Town gas* Syngas* Mond gas* Propane* Butane* Regasified liquified petroleum gas* Wood gas...

, oils, solid residue (char), and low-grade carbon black

Carbon black

Carbon black is a material produced by the incomplete combustion of heavy petroleum products such as FCC tar, coal tar, ethylene cracking tar, and a small amount from vegetable oil. Carbon black is a form of amorphous carbon that has a high surface-area-to-volume ratio, although its...

, which cannot be used in tire manufacture. A pyrolysis method which produces activated carbon

Activated carbon

Activated carbon, also called activated charcoal, activated coal or carbo activatus, is a form of carbon that has been processed to make it extremely porous and thus to have a very large surface area available for adsorption or chemical reactions.The word activated in the name is sometimes replaced...

and high-grade carbon black has been suggested.

Recent developments in devulcanization enable dealing with substantial volumes, taking 40 mesh whole tire crumb and converting it into value-added compounds without degrading the polymer and without generating any pollution. This new generation in devulcanization technologies operates with very high productivity while maintaining a low energy footprint. The compounds produced from processed tire scrap can be blended with virgin rubber compounds, maintaining performance while substantially reducing the raw material cost. The substantial economies of scale

Economies of scale

Economies of scale, in microeconomics, refers to the cost advantages that an enterprise obtains due to expansion. There are factors that cause a producer’s average cost per unit to fall as the scale of output is increased. "Economies of scale" is a long run concept and refers to reductions in unit...

and value addition now make it possible to make burning of tires entirely unnecessary.

Tire pyrolysis

The pyrolysis

Pyrolysis

method for recycling used tires is a technique which heats whole or shredded tires in a reactor vessel containing an oxygen free atmosphere and a heat source. In the reactor the rubber is softened after which the rubber polymers continuously breakdown into smaller molecules. These smaller molecules eventually vaporize and exit from the reactor. These vapors can be burned directly to produce power or condensed into an oily type liquid, generally used as a fuel. Some molecules are too small to condense. They remain as a gas which can be burned as fuel. The minerals that were part of the tire, about 40% by weight, are removed as a solid. When performed well a tire pyrolysis process is a very clean operation and has nearly no emissions or waste.

The properties of the gas, liquid and solid output are determined by the type of feed stock used and the process conditions. For instance whole tires contain fibers and steel. Shredded tires have most of the steel and sometimes most of the fiber removed. Processes can be either batch or continuous. The energy required to drive the decomposition of the rubber include using directly fired fuel (like a gas oven), electrical induction (like an electrically heated oven) or by microwaves (like a microwave oven). Sometimes a catalyst is used to accelerate the decomposition. The choice of feedstock and process can impact the value of the finished products.

The historical issue of tire pyrolysis has been the solid mineral stream which accounts for about 40% of the output. The steel can be removed from the solid stream with magnets for recycling. The remaining solid material, often referred to as "char", has had little or no value other than possibly as a low grade carbon fuel. Char is the destroyed remains of the original carbon black used to reinforce and provide abrasion resistance to rubber. The solid stream also includes the minerals used in rubber manufacturing. This high volume component of tire pyrolysis, until recently, has made the economic viability very difficult to achieve. Over the past five years two or three companies have discovered ways to recover the carbon in its original form. These companies have been commercially producing and selling recovered carbon black based products that successfully supplement virgin carbon black in rubber and plastics.

Markets

A report from 2003, cited by the EPA, says that markets ("both recycling and beneficial use") existed for 80.4% of scrap tires, about 233 million tires per year. Assuming 22.5 lbs per tire, the 2003 report predicts a total weight of about 2.62 million tons from tires.

The markets predicted by the 2003 report were: tire derived fuel (TDF) using 130 million tires, civil engineering projects using 56 million tires, ground rubber turned into molded rubber products using 18 million tires, ground rubber turned into rubber-modified asphalt using 12 million tires, Exported items using 9 million tires, cut, stamped and punched products using 6.5 million tires, and agricultural and miscellaneous uses 3 million tires.

Tire-derived products stage

Second stage of tire recycling involves the production of alternate products for sale. New products derived from waste tires generate more economic activity than combustion or other low multiplier production, while reducing waste stream without generating excessive pollution and emissions from recycling operations.

Tire-derived products

Whole tires can be reused in many different ways. One way is for a steel mill to use the tires as a carbon source, replacing coal or coke in steel manufacturing. Instead of mining coal from the ground and then burying tires in landfills, the tires are used directly. Tires are also bound together and used as different types of barriers such as: collision reduction, erosion control, rainwater runoff, wave action that protects piers and marshes, and sound barriers between roadways and residences. Entire homes can be built with whole tires by ramming them full of earth and covering them with concrete, known as Earthship
Earthship
An earthship is a type of passive solar house made of natural and recycled materials. Designed and marketed by Earthship Biotecture of Taos, New Mexico, the homes are primarily constructed to work as autonomous buildings and are generally made of earth-filled tires, using thermal mass...

s.

Some Artificial reef

Artificial reef

An artificial reef is a human-made underwater structure, typically built to promote marine life in areas with a generally featureless bottom, control erosion, block ship passage, or improve surfing....

s are built using tires that are bonded together in groups, there is some controversy on how effective tires are as an artificial reef system, an example is The Osborne Reef

Osborne Reef

Osborne Reef is an artificial reef off the coast of Fort Lauderdale, Florida constructed of concrete jacks in a diameter circle.In the 1970s, the reef was the subject of an ambitious expansion project utilizing old and discarded tires...

Project.

The process of stamping and cutting tires is used in some apparel products, such as sandals and as a road sub-base, by connecting together the cut sidewalls to form a flexible net.

Chipped and shredded tires are used as Tire Derived Fuel (TDF); this is not the same as recycling, but TDF helps to eliminate tires from our waste stream and produces a fuel source. They are used in civil engineering applications such as sub grade fill and embankments, backfill for walls and bridge abutments, sub grade insulation for roads, landfill projects, and septic system drain fields.

Shredded tires, known as Tire Derived Aggregate (TDA), have many civil engineering applications. TDA can be used as a backfill for retaining walls, fill for landfill gas
Landfill gas
Landfill gas is a complex mix of different gases created by the action of microorganisms within a landfill.-Production:Landfill gas production results from chemical reactions and microbes acting upon the waste as the putrescible materials begins to break down in the landfill...

trench collection wells, backfill for roadway landslide repair projects as well as a vibration damping material for railway lines.

Ground and crumb rubber, also known as size-reduced rubber, can be used in both paving type projects and in moldable products. These types of paving are: Rubber Modified Asphalt (RMA), Rubber Modified Concrete, and as a substitution for an aggregate. Examples of rubber-molded products are carpet padding or underlay
Underlay
Underlay or underlayment generally refers to a thin layer of cushioning made of materials such as sponge rubber, foam, felt, or crumb rubber; this material is laid beneath carpeting to provide comfort underfoot, to reduce wear on the carpet, and to provide insulation against sound, moisture, and...

, flooring materials, dock bumpers, patio decks, railroad crossing blocks, livestock mats, sidewalks, rubber tiles and bricks, moveable speed bumps, and curbing/edging. The rubber can be molded with plastic for products like pallets and railroad tie
Railroad tie
A railroad tie/railway tie , or railway sleeper is a rectangular item used to support the rails in railroad tracks...

s. Athletic and recreational areas can also be paved with the shock absorbing rubber-molded material. Rubber from tires is sometimes ground into medium-sized chunks and used as rubber mulch
Rubber mulch
Rubber mulch is a type of mulch used in gardens and sustainable landscaping that is made from 100% recycled rubber.-Composition:Rubber mulch generally consists of either waste tire buffings or nuggets of rubber from tires that are ground up whole, after having their steel bands removed...

. Rubber crumb can also be used as an infill, alone or blended with coarse sand, as in infill for grass-like synthetic turf products such as FieldTurf
FieldTurf
FieldTurf is a brand of artificial turf playing surface. It is manufactured and installed by the FieldTurf Tarkett division of Tarkett Inc., based in Calhoun, Georgia, USA. In the late 1990s, the artificial surface changed the industry with a design intended to replicate real grass...

.

Environmental concerns

Due to heavy metals

Heavy metals

A heavy metal is a member of a loosely-defined subset of elements that exhibit metallic properties. It mainly includes the transition metals, some metalloids, lanthanides, and actinides. Many different definitions have been proposed—some based on density, some on atomic number or atomic weight,...

and other pollutants in tires there is a potential risk for the (leaching

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....

) of toxins into the groundwater when placed in wet soils. This impact on the environment varies according to the pH level and conditions of local water and soil. Research has shown that very little leaching occurs when shredded tires are used as light fill material; however, limitations have been put on use of this material; each site should be individually assessed determining if this product is appropriate for given conditions.

Ecotoxicity may be a bigger problem than first thought . Studies show that zinc, heavy metals, a host of vulcanization

Vulcanization

Vulcanization or vulcanisation is a chemical process for converting rubber or related polymers into more durable materials via the addition of sulfur or other equivalent "curatives." These additives modify the polymer by forming crosslinks between individual polymer chains. Vulcanized material is...

and rubber chemicals leach into water from tires. Shredded tire pieces leach much more, creating a bigger concern, due to the increased surface area on the shredded pieces. Many organisms are sensitive, and without dilution, contaminated tire water has been shown to kill some organisms.

External links

European Tyre Recycling Association
European Tyre & Rubber Manufacturers' Association
Rubber Manufacturers Association, United States
International Institute of Synthetic Rubber Producers, Inc., non-profit organization

News

Giant microwave turns plastic back to oil, New Scientist
New Scientist
New Scientist is a weekly non-peer-reviewed English-language international science magazine, which since 1996 has also run a website, covering recent developments in science and technology for a general audience. Founded in 1956, it is published by Reed Business Information Ltd, a subsidiary of...

, 2007-06-26

The source of this article is wikipedia, the free encyclopedia. The text of this article is licensed under the GFDL.