A Short Introduction To Glass Recycling

Glass is one of the few materials that can be repeatedly recycled with little or no effect on its strength, quality, or integrity. Q&As in this blog entry include:

1. What is glass made of?
2. How is glass recycled?
3. Should you break glass prior to recycling it?
4. Should you separate non-container from container glass when recycling?
5. Should you separate glass by color?
6. Should you wash glass before you recycle it?
7. Is glass recycling difficult?

1. What is glass made of?

Glass is primarily composed of three materials:

Ø  Sand, aka sodium silicate (SiO2)

Ø  Limestone, aka calcium carbonate (CaCO3)

Ø  Soda ash, aka sodium carbonate (Na2CO3)

These are heated together in a furnace at 3,090o F until liquified. As this molten mixture cools, it hardens more quickly than its molecules can “settle,” making it easily moldable into many different shapes and things. E.g., bottles, glassware, bowls, appliance parts, and decorative items.

Attesting to the desirability of glass recycling, much of it’s manufactured by adding cullet to the sand/limestone/soda ash mixture, where “cullet” is the industry term for furnace-ready recycled scrap glass.

2. How is glass recycled?

Unwanted glass is collected from homes, businesses, and public recycling bins and brought to a recycling facility where it’s initially sorted by type and color, followed by further sorting to remove contaminants, labels, caps, etc.

The glass is then cleaned to remove any remaining impurities before being crushed into small pieces (i.e., cullet), which is mixed with other raw materials (sand, limestone, and soda ash) to make new glass products.

This mixture is heated in a furnace at 3,090o F until liquified. Then, it’s formed into new glass containers or products, and slowly cooled to prevent stress and cracking.

3. Should you break glass prior to recycling it?

No. This is because glass is preferred “whole” in most recycling programs, as it’s easier to sort than if it were in many little pieces. If glass pieces are too small to be easily sorted, they wind up being combined and yielding a lower quality glass than what’s obtainable from discrete batches of cullet.

4. Should you separate non-container from container glass when recycling?

Yes. Non-container glass (e.g., from windows, mirrors, optical equipment, etc.) is typically treated with chemicals. Not only does this potentially contaminate the sand/limestone/soda ash mixture, it affects the melting point of the cullet. So, glass recyclers prefer that you separate one from the other.

5. Should you separate glass by color?

It depends. Because glass can be recycled repeatedly, it’s desirable to maintain its original color from generation to generation. Mixing different colors of cullet militates against this. Thus, some recyclers require that you segregate clear, green, and brown glass. However, some “single stream” recyclers don’t require you to sort by color. They do it themselves.

6. Should you wash glass before you recycle it?

Yes. Although the glass is washed before processing, it can attract vermin and become malodorous during storage and transport if it contains food residue or other contaminants.

7. Is glass recycling difficult?

Glass recycling conserves natural resources, reduces the need for raw materials, and lowers energy consumption. Yet, there are some onsite challenges. Among them:

Glass weighs more than other waste (e.g., aluminum) and isn’t as flexible as others (e.g., cardboard). This can make storing glass cumbersome and transporting it to a recycling facility costly and energy-intensive. Thus, an efficient collection and transportation system is crucial to keeping the process economical.

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