Humans did not invent glass making: long before humans learned the secret nature was making glass. When lightning struck sand it melted it into long, thin tubes of glass. Erupting volcanoes melted rocks and sand into glass. Humans found this naturally made glass and improved the process. The earliest glass made by humans was probably a glaze on ceramic pottery made somewhere around 3,000 B.C.
Today sand, soda ash, lime, and sometimes gypsum or dolomite are melted together in large furnaces to over 2,000 degrees Fahrenheit until the mixture becomes a syrupy mass. While malleable it can be shaped by blowing to make hollow vessels, drawing into sheets or tubes, pressing into a mold, or sculpting things with globs of hot glass.
Colored glass is produced by adding small amounts of natural elements to the molten glass. For instance, brown glass is made by adding iron, sulfur and carbon to the mix.
Producing virgin glass takes less energy than does producing metal or plastic and glass recycles endlessly without losing any of its strength. Also, glass containers are far more stable than plastic or metal containers so they do not leech or out-gas anything into the food they contain and glass containers can be safely reused over and over.
Crushed recycled glass is called ‘cullet’. The proportion of cullet in new glass can be as high as 90%. Cullet melts at a lower temperature so for every 10% of cullet in the glass mix, the factory can use 2% less energy to produce the same quality of glass.
While glass is made from all naturally occurring materials, nature cannot recover glass through decomposition as it will with some other products. If dumped into a landfill, glass will remain there, taking up space, forever – OK, a million years or so: pretty much forever. Because it does not contain or release any toxins, it is safe to dispose of glass this way, but trashing glass removes a valuable resource from the materials chain.
Advantages of Recycling Glass
Recycling Glass is Sustainable
Glass containers are 100-percent recyclable, which means they can be recycled repeatedly, again and again, with no loss of purity or quality in the glass.
Recycling Glass is Efficient
Recovered glass from recycling is the primary ingredient in all new glass containers. A typical glass container is made of as much as 70 percent recycled glass. According to industry estimates, 80 percent of all recycled glass eventually ends up as new glass containers.
Recycling Glass Conserves Natural Resources
Every ton of glass that is recycled saves more than a ton of the raw materials needed to create new glass, including: 1,300 pounds of sand; 410 pounds of soda ash; and 380 pounds of limestone.
Recycling Glass Saves Energy
Producing new glass means heating sand and other substances to a temperature of at least 2,600 degrees Fahrenheit, which requires a lot of energy and creates a lot of industrial pollution. Making recycled glass products from cullet consumes 40 percent less energy than making new glass from raw materials, because cullet melts at a much lower temperature.
Recycling Glass Saves Money and Helps the Environment
Cullet costs less than the raw materials needed to make glass. Using cullet prolongs furnace life and saves energy since it melts at a lower temperature. Less energy used means reduced emissions of nitrogen oxide and carbon dioxide as well as reduced fuel costs.
Recycled Glass is Useful
Besides serving as the primary ingredient in new glass containers, recycled glass also has many other commercial uses—from creating decorative tiles, insulation and landscaping material to rebuilding eroded beaches.
Recycling Glass is Simple
Glass is one of the easiest materials to recycle. Other than separating and crushing, little preparation is required. Most collection points have separate bins for clear, green and amber. Glass recyclers require separation by color as the different colors of glass are chemically incompatible. NOTE: Heat-resistant glass like Pyrex or borosilicate glass should not be disposed of in the glass container as even a single piece of such material will alter the viscosity of the fluid in the furnace.
Recycling Glass Pays
Several U.S. states offer cash refunds for most glass bottles. In these states recycling glass can actually put a little extra money in your pocket.
How Is Recycled Glass Sorted?
When recycling glass, sorting the glass by color can be done manually using separate bins for the different colors which are kept separate all the way to the crusher.
Modern systems use technology to separate foreign materials from the glass. Conveyors can use blowers to remove paper, float tanks to remove plastic, toss bins to remove aluminum and magnets to remove steel from the flow of crushed glass.
The tricky part uses beams of colored light, sensors and kickers to separate glass in a unified stream into separate streams of clear, amber and green glass. It often takes several passes to produce pristine separation, but this is all automated and requires very little human labor in the process.
Fines too small to be reliably separated are sold as a tri-color mix to companies like Owens Corning who make fiberglass insulation from it.
This glass separation center is a large and expensive complex, so most communities collect the glass and sell it to these centers rather than processing it themselves. Here is a brief look at the separation process:
If your community does not collect glass, ask your waste management service to seek out a buyer and start recycling glass. It generally adds very little to the process and adds another revenue stream to the service.
- http://www.youtube.com/watch?feature=player_embedded&v=LUF_5zrFG9c glass bottles
- http://www.youtube.com/watch?feature=player_embedded&v=4j1hafqSyG0 sheet glass
- http://www.youtube.com/watch?feature=player_embedded&v=IjNusHQOhTM window glass