 | The common glass (soda-lime glass) is surprisingly friendly when it comes to the environment. It uses common, easy to extract materials, the production process does not generate much waste, and the recycling ratios of glass are one of the highest of all materials (about 50% in US, 60% in UK, up to 95% in Switzerland).
Glass is composed of about 70% silica (silicon oxide, or, basically, sand), 15% soda (sodium carbonate), 15% lime (calcium oxide, usually made on site from limestone), and minor amounts of other additives. Thus the name of the common glass: soda-lime glass. Glass is used in huge variety of product, but vast majority is made into windows or into containers. For many uses glass needs to be made with different additives. For example, replacing the lime with lead oxide produces "crystal" glass, replacing soda and lime with boron oxide produces borosilicate glasses such as Pyrex, etc. However, we do not consider these specialty glasses in this article.The production of glass is composed of three major parts:
- preparation of raw materials (here, for example, a lot of water is used -- to wash the recycled bottles...);
- melting (here the most energy is used - usually in form of burning of natural gas);
- forming and annealing (where the products assume their final shapes).
The information about the production process of the glass is taken from the British Glass website, and in particular, from excellent publication "UK Manufacture - a mass balance study 2008". We realize that the data contained there is specific to the UK, however, glass production is mature and standardized enough to extend this data to cover the world average.
|
