The process of glass recycling

To be recycled into more glass products, glass needs to be separated first into colours: green, brown and clear.

In Taranaki the colour sort is done at collection - as shown in this video.

It is then crushed into small pieces called cullet. Cullet is a very valuable material in the production of new glass as it helps the batch melt quickly and reduces the energy required by the furnaces by 20-25%.

Not all recycled glass is used to make new glass. Crushed glass is used as a feedstock for other industries, though most of these applications are international rather than New Zealand based .

Many large fibreglass plants are using over 30% recycled glass content for new products.

Crushed glass is being used by the world’s leading manufacturer of reflective glass beads designed for highway and airport traffic safety use. Scarce natural minerals can be replaced by using crushed glass in the manufacture of road paints, as in Canada.

There are also an increasing number of specialty end use markets, some of which are used here in New Zealand. Crushed glass is used as an alternative to sand for sandblasting, as a filter in swimming pools, as an abrasive cleaner for fine jewellery and as a small percentage of road construction material.

Benefits of glass recycling

Glass is made from natural materials including sand, soda ash and limestone. It is infinitely recyclable and doesn't reduce in quality, unlike plastic which downgrades and can only be recycled a limited number of times. All new glass containers made in New Zealand contain recovered materials from recycled glass. 

Every tonne of glass that is recycled saves more than a tonne of the raw materials needed to create new glass so reduces the need for quarrying.

Making new glass means heating sand and other substances to a temperature of about 1550 degrees Celsius, which requires a lot of energy and creates a lot of industrial pollution, including greenhouse gases. One of the first steps in glass recycling is to crush the glass and create a product called “cullet.” 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.

Because glass is made from natural and stable materials such as sand and limestone, glass containers have a low rate of chemical interaction with their contents. As a result, glass can be safely reused, for example as refillable water bottles.

Glass itself is not regarded as a threat to the environment because it is inert. If subjected to weathering forces, glass will break down into small particles of silica, which is one of the most common elements on earth. There are adverse effects on the environment from the original mining for the glass making ingredients.

Action and Awareness in New Zealand

The Glass Packaging Forum (GPF) promotes the environmental benefits of glass packaging and manages the accredited Glass Packaging Forum Product Stewardship Scheme.

The Glass Forum financially supports promoting recycling at events and /or programmes designed to raise awareness about glass recovery.