How stuff is recycled
First published February 2010, last updated November 2012
Our busy modern lives disconnect us from all sorts of things – how food is grown, how goods are produced, our waste dealt with, and the processes behind recycling. The following is a brief overview how some products are recycled past the point of extraction from the waste stream.
Aluminum can recycling process
After arriving at a smelter and inspected, the crushed aluminum cans are shredded. The pieces are then heated to remove the paint and any moisture, after which the material passes over fine screens to remove contaminants.
The material is heated again to melting point (around 600C) and chemicals added to separate more impurities that are then skimmed off. Aluminium and other metals may then be added to bring molten material to the required alloy specification.
The molten aluminum is poured into very large ingots and once cooled and cleaned, sent through rollers multiple times until a thin sheet is produced; which can then be remade into cans.
It’s an energy intensive process, but the recycling energy savings are around 95% compared to mining and smelting from new raw materials and aluminium can be recycled an unlimited number of times.
Steel can recycling process
After arriving at a steel smelter, bales of crushed cans are placed in a furnace with other recyclable steel. Molten iron is added and oxygen is pumped into the furnace, which heats up to around 1700 degrees Celsius, for 30 minutes. By the end of this time, impurities have been driven or skimmed off.
The molten steel is poured into large ingots, which go through multiple rollers while still very hot until the desired thickness is achieved for making products such as cans.
While the steel can recycling process doesn’t have as many stages as aluminium cans, much higher temperatures are used therefore requiring more energy. Regardless, the recycling energy savings are around 62 – 74%. Steel can be recycled over and over in this way.
Plastic soda bottles and bottled water containers
This deals specifically with PETE (or PET) plastics (plastic resin code 1).The bottles are first inspected for foreign materials then sorted into colors. The bottles are then sterilised, crushed and chopped into flakes.
The flakes undergo another separation and cleaning process to remove remaining foreign materials. The flakes are then chemically reverse engineered by either methanolysis or glycolosis, which can restore the material to the original raw materials and blended to create new PET.
The recycling energy savings of plastic soda and water bottles is around 90%.
Glass bottle and jar recycling process
Glass bottles are separated by color and broken into small pieces, usually at a recycling center, in order to cut down on volume for shipping. They are then transported to a bottle making plant where the material is crushed. Magnets, filters and vacuums remove foreign objects such as labels and metals. The cleaned powdered glass, known as cullet, is mixed with raw materials and placed in a furnace which melts it into molten glass; ready to be formed into new bottles and jars.
Glass recycling uses only two-thirds the energy needed to manufacture glass from raw materials.
Paper recycling process
The paper is sorted according to quality and shipped to a paper mill where water is added in order to turn it into a pulp. Foreign matter is then removed by various filters and screens. Chemicals are added to remove the ink from the pulp. Depending on the type of process, de-inking can be a simple detergent process or one that may involve chlorine or other more harmful chemicals depending on the ink being removed. The ink used in newspapers and packaging these days is usually soy-based; however, copy machine and laser printed document “ink” is a plastic polymer burned onto the page that requires harsher processes to remove.
Once de-inked, pulp is flushed with more water and air is injected to form an inky foam that is skimmed. The remaining water is drained and reused. The pulp is then bleached – more often with hydrogen peroxide these days as chlorine can combine with organic materials to form dioxins – one of the most deadly of man-made poisons.
More chemicals may be added at that point and the final pulp is either pressed into sheets and dried or mixed in with virgin pulp.
Recycling paper uses about 60% less energy than making paper from new materials; however, each time paper is recycled, it loses quality – so in effect it is really downcycled each time. Given the wide range of processes that may be used, not all recycled paper is created equal from an environmental aspect.
Another product often recycled is motor oil – most people don’t realize that motor oil can be fully recycled into new motor oil as it never wears out; it just gets dirty. I describe the motor oil recycling process here.
As you can see from above – recycling isn’t all that straightforward and there can be a lot of chemicals involved. We all need to continue recycling of course, but reducing consumption is equally as important. For example, perhaps next time you feel like a can of soda, consider heading to the tap for a glass of water instead. Instead of buying newspaper, duck online and read it there.
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