Glass Recycling

Did you know?

• Over 12,000 tonnes of glass were collected for recycling in Canberra in 2005-06
• Only about one third of glass containers (bottles and jars) are recycled in Australia.  The goal by 2010 is for this to have increased to 55%.
• Making glass from recycled material requires only 40% of the energy necessary to make glass from sand.
• Visy Recycling Glass Division recycles around 450,000 tonnes of glass each year.

Introduction

The discovery of glass dates back to the Phoenicians more than 5,000 years ago, while the method of hand blowing glass bottles is believed to have been invented by the Egyptians in the First Century BC. For 2,000 years, hand blowing glass bottles continued to be the principal way of making glass bottles. However, during the last hundred years or so, mechanised glass blowing techniques have revolutionised the production of glass containers, allowing bottles to be produced quickly and cheaply. Today, glass containers are widely used to package a huge array of foods and drinks.

Manufacture

The three main raw materials used to make glass containers are sand (to provide silica), soda ash (to reduce the melting point) and limestone (to increase hardness). Crushed glass, called cullet, is now the major raw material for glass manufacturing in Australia. Other ingredients are used in small amounts, the proportions of each depending on the type of glass required. To make glass containers the mix of ingredients, known as a batch, is fed continuously into furnaces and melted at about 1,500 degrees C. The molten glass from the furnaces is then conveyed to moulding machines where globules of glass are dropped into moulds. Air is blown into the hot globules to form bottles, which are cooled slowly and then despatched to bottling plants for filling.

Recycling

Bottles and jars collected in recycling schemes are sorted into clear, amber and green glass. This is either done manually or through the use of sophisticated technology which sees and sorts according to colour (these machines can also remove contaminants at this point).  Otherwise, containers of different coloured glass are then taken to a beneficiation plant to upgrade the quality of the waste glass before reprocessing. At these plants, contaminants such as metals, plastic, china, ceramics and stones are removed, and the glass is crushed. The cullet is transported to the glass-making factory where it is used with the other batch materials to make new glass containers.

According to ACI Glass Packaging, new glass bottles may be made with up to 100% cullet. However, "The actual percentage depends on the quantity and quality of cullet available. In Australia today, cullet represents, on average, 45% of the batch materials" (ACI Glass Packaging, 1997) There may be some energy savings in using cullet in glass manufacture, but the savings depends on the percentage of cullet used. Using cullet, however, does save resources. Each tonne of cullet saves 1.1 tonnes of raw materials.

Lightweighting

Glass manufacturers today make glass bottles that are much lighter than bottles made in previous years. This process, called 'lightweighting', saves considerable amounts of energy and raw materials. ACI Glass Packaging state that a 'stubby' beer bottle made in 1986 weighed 260 g, but by 1994, the same size 'stubby' weighed only 180 g. This is a reduction of 31%. By 2000, it is expected that these bottles will weigh 170g.

Sources

ACI Glass Packaging, poster and brochure (1997).

Beverage Industry Environment Council, 1996, Recycling Audit and Garbage Bin Analysis, June-September.

Visy Recycling, online: http://www.visy.com.au/recycling/