Recycling Techniques

Ever wonder how different types of materials get recycled? Check out this list of commonly recycled materials.

Recycling Techniques

Aggregates & concrete

Concrete aggregate collected from demolition sites is put through a crushing machine, often along with asphalt, bricks, dirt, and rocks. Smaller pieces of concrete are used as gravel for new construction projects. Crushed recycled concrete can also be used as the dry aggregate for brand new concrete if it is free of contaminants.


The large variation in size and type of batteries makes their recycling extremely difficult: they must first be sorted into similar kinds and each kind requires an individual recycling process. Additionally, older batteries contain mercury and cadmium, harmful materials which must be handled with care.

Biodegradable waste

Biodegradable waste can be recycled into useful material by biological decomposition. There are two mechanisms by which this can occur. The most common mechanism of recycling of household organic waste is home composting or municipal kerbside collection of green wastes sent to large scale composting plants.

Alternatively organic waste can be converted into biogas and soil improver using anaerobic digestion. Here organic wastes are broken down by anaerobic microorganisms in biogas plants. The biogas can be converted into renewable electricity or burnt for environmentally friendly heating. Advanced technologies such as mechanical biological treatment are able to sort the recyclable elements of the waste out before biological treatment by either composting, anaerobic digestion or biodrying.

Electronics disassembly and reclamation

The direct disposal of electrical equipment—such as old computers and mobile phones is banned in many areas due to the toxic contents of certain components. The recycling process works by mechanically separating the metals, plastics and circuit boards contained in the appliance. When this is done on a large scale at an electronic waste recycling plant, component recovery can be achieved in a cost-effective manner.

Electronic devices, including audio-visual components (televisions, VCRs, stereo equipment), mobile phones and other hand-held devices, and computer components, contain valuable elements and substances suitable for reclamation, including lead, copper, and gold. They also contain a plethora of toxic substances such as dioxins, PCBs, cadmium, chromium, radioactive isotopes, and mercury. Additionally, the processing required to reclaim the precious substances (including incineration and acid treatments) release, generate and synthesize further toxic byproducts.

In the United States, an estimated 70% of heavy metals in landfills come from discarded electronics. Some regional governments are attempting to curtail the accumulation of electronics in landfills by passing laws obligating manufacturers and consumers to recycle these devices, but because in many cases safe dismantlement of these devices in accordance with first world safety standards is unprofitable, historically much of the electronic waste has been shipped to countries with lower or less rigorously-enforced safety protocols. Places like Guiyu, China dismantle tonnes of electronics every year, profiting from the sale of precious metals, but at the cost of the local environment and the health of its residents.

Mining to produce the same metals, to meet demand for finished products in the west, also occurs in the same countries, and the United Nations Conference on Trade and Development (UNCTAD) has recommended that restrictions against recycling exports be balanced against the environmental costs of recovering those materials from mining. Hard rock mining in the USA produces 45% of all toxics produced by all USA industries (2001 US EPA Toxics Release Inventory).

Printer ink cartridges & toners

Printer ink cartridges can be recycled. They are sorted into different brands and models which are then resold back to the companies that created these cartridges. The companies then refill the ink reservoir which can be sold back to consumers. Toner cartridges are recycled the same way as ink cartridges, using toner instead of ink. This method of recycling is highly efficient as there is no energy spent on melting and recreating the recycled object itself.

Ferrous metals

Iron and steel are the world's most recycled materials, and among the easiest materials to recycle, as they can be separated magnetically from the waste stream. Recycling is via a steelworks: scrap is either remelted in an Electric Arc Furnace (90-100% scrap), or used as part of the charge in a Basic Oxygen Furnace (around 25% scrap). Any grade of steel can be recycled to top quality new metal, with no 'downgrading' from prime to lower quality materials as steel is recycled repeatedly. 42% of crude steel produced is recycled material.

Non-ferrous metals

Aluminium is shredded and ground into small pieces. These pieces are melted in an aluminium smelter to produce molten aluminium. By this stage the recycled aluminium is indistinguishable from virgin aluminium and further processing is identical for both.

Due to the large amount of energy required to extract aluminum from ore and it's low melting point, the environmental benefits of recycling aluminium are enormous. Approximately 5% of the CO2 is produced during the recycling process compared to producing raw aluminium (and an even smaller percentage when considering the complete cycle of mining and transporting the aluminium). Also, as open-cut mining most often used for obtaining aluminium ore, mining destroys large sections of natural land.

For example, an aluminium can is 100% recyclable every time it is recycled, it saves enough energy to watch television for about three hours (compared to mining and producing a new can).


Glass bottles and jars are gathered via curbside collection schemes and bottle banks, where the glass is sorted into color categories. The collected glass cullet is taken to a glass recycling plant where it is monitored for purity and contaminants are removed. The cullet is crushed and added to a raw material mix in a melting furnace. It is then mechanically blown or molded into new jars or bottles. Glass cullet is also used in the construction industry for aggregate and glassphalt. Glassphalt is a road-laying material which comprises around 30% recycled glass. Glass can be recycled indefinitely as its structure does not deteriorate when reprocessed.


Recycled paper is made from waste paper, usually mixed with fresh wood pulp. If the paper contains ink, it must be deinked. This also removes fillers, clays, and fiber components.

Almost all paper can be recycled today, but some types are harder to recycle than others. Kraft paper, papers coated with plastic or aluminum foil, and papers that are waxed, pasted, or gummed are usually not recycled because the process is too expensive. Different types of paper are usually sorted before recycling, such as newspapers and cardboard boxes.

Different grades of paper are recycled into different types of new products. Old newspapers are usually made into new newsprint, egg cartons, or paperboard. Old corrugated boxes are made into new corrugated boxes or paperboard. High-grade white office paper can be made into almost any new paper product: stationery, newsprint, magazines, or books.

Sometimes recyclers ask for the removal of the glossy inserts from newspapers because they are a different type of paper. Glossy inserts have a heavy clay coating that some paper mills cannot accept. Since the paper is weighed down by the clay coating, a paper mill gets more recyclable fibers from a ton of pure newsprint.

Paper can only be recycled a finite number of times due to the shortening of paper fibers making the material less versatile. Often it will be mixed with a quantity of virgin material, referred to as downcycling. This does not however exclude the material from being used in other processes such as composting or anaerobic digestion, where further value can be extracted from the material in the form of compost or biogas.


Plastic recycling is the process of recovering scrap or waste plastics and reprocessing the material into useful products. Compared to glass or metallic materials, plastic poses unique challenges - because of the massive number of types of plastic, they each carry a resin identification code, and must be sorted before they can be recycled. This can be costly - while metals can be sorted using electromagnets, no such 'easy sorting' capability exists for plastics. In addition to this, while labels do not need to be removed from bottles for recycling, lids are often made from a different kind of non-recyclable plastic.

Plastics recycling rates lag far behind those of other items, such as newspaper and aluminium; consumers are typically unsure of how to recycle plastics, and compared to paper and metals fewer recycling facilities exist.

Finally, recycled plastic is less appealing to manufacturers than new plastic.


A form of metal recovery associated to recycling is "shipbreaking". This is the process of breaking a ship into smaller, recyclable pieces of metal. It often has a number of major drawbacks to the local community and the local environment where shipbreaking occurs.

Shipbreaking tends to occur in poor countries where lack of or insufficient safety standards, labor laws and wage agreements makes them a lucrative area for demolition work. India, Pakistan, Turkey and Bangladesh make up the majority of these countries.

Toxic material in the form of metals, gas, fumes and exhaust often contaminate a large area surrounding the ship breaking yards, including nearby villages and sleeping quarters for the workers, which are commonly placed nearby the yards.

Material such as paint, electrical equipment, wire, anodes and coatings are often burned or simply dumped in the dismantling process. This releases metals such as mercury, lead, arsenic and chromium.

Polychlorinated organic compounds are another source of toxic material that can be found in transformers and cable insulation often burned or dumped in and around the ship breaking yard.

It is believed that many of the social, economical and environmental drawback in shipbreaking could be alleviated greatly by adhering to safe handling of the recycling process, or the ship owner decontaminating the toxins from the ship before it gets sent to be demolished.


When considering textile recycling one must understand what the material consists of. Most textiles are composites of cotton (biodegradable material) and synthetic plastics. The textile's composition will affect its durability and method of recycling.

Workers sort and separate collected textiles into good quality clothing and shoes which can be reused or worn. These sorting facilities are in a trend of being moved from developed countries such as the UK to developing countries.

Damaged textiles are further sorted into grades to make industrial wiping cloths and for use in paper manufacture or material which is suitable for fibre reclamation and filling products. If textile reprocessors receive wet or soiled clothes however, these may still end up being disposed of in landfill, as the washing and drying facilities are not present at sorting units.

Fibre reclamation mills sort textiles according to fibre type and colour. Colour sorting eliminates the need to re-dye the recycled textiles. The textiles are shredded into "shoddy" fibres and blended with other selected fibres, depending on the intended end use of the recycled yarn. The blended mixture is carded to clean and mix the fibres and spun ready for weaving or knitting. The fibres can also be compressed for mattress production. Textiles sent to the flocking industry are shredded to make filling material for car insulation, roofing felts, loudspeaker cones, panel linings and furniture padding.