Editorial Feature

Glass Recycling - An Introduction

Jan 4 2013

Glass is a non-crystalline material that is optically transparent and brittle. Glass is obtained from three key substances that include limestone, sand and baking soda. Glass is a recyclable material and can be easily disposed without causing much harm to the environment.

Glass is available in a number of varieties including but not limted to:

Laminated glass
Flat glass
Tempered safety glass
Float glass
Self cleaning glass
Mirrors
Safety glass
Picture frame glass
Patterned glass
Energy efficient glass
Sheet glass

Characteristics of Glass

Following are the significant characteristics of glass:

It is not affected by most chemicals and also by weather
It can be molded or blown into different shapes
Glassware with heat resistant properties can withstand high temperatures levels
It is a hygienic material and does not have any toxic substances
It is resistant to wear and tear
It is possible to sterilize glass containers without altering the solution inside
It can be re-melted very often
It is a biologically inactive and inert material
It has an amorphous and disordered structure
Commercial glass has a nonporous and smooth surface
Glass does not stain, deteriorate and corrode

Manufacturing Process of Glass

The manufacturing process of glass involves four significant steps that include the following:

Preparation of raw material
Melting in a furnace
Forming
Finishing.

These four steps are mostly used to manufacturer all glass varieties except for a few changes in the forming and finishing processes.

The first step is to crush the raw materials that include soda ash, sand and limestone. These crushed materials are then stored in elevated bins.
The materials are transferred to a weigher and mixer through a gravity feed system and mixed with cullet
From here, the mixture is sent into a batch storage bin that stores the mixture and then drops the mixture into the melting furnace that is capable of producing between 50 and 300 t of glass on a daily basis
The mixture passes the feeder to enter the melting furnace and remains on the top surface of the molten glass in the furnace
The mixture melts and passes through the melter and goes into the refiner
The molten glass is heat conditioned in the refiner and is now ready for the forming process
The molten glass is now ready to be shaped by pressing and blowing, pressing, drawing, blowing, floating or rolling
The product obtained after these processes enters the final stage of coating and annealing

Applications of Newly Manufactured Glass

The applications of glass include:

Electrical transmission and illumination
Optical and scientific research instruments
Architectural applications
It is used to make doors and windows for commercial and domestic buildings, car safety windows, computer screens, picture tubes in television sets, kitchenware, etc.
The most recent usage of glass is to connect computer centers and telephone calls using glass fibers

Environmental Impact of Glass Disposal

The manufacturing process of glass pollutes the environment by emitting carbon dioxide, sulfur dioxide and nitrogen oxides. Emissions of dust during the mixing, storage, handling and transportation processes pollute the environment.

Reduction in dust emissions can be brought about using closed convectors, efficient loading and unloading processes, enclosed silos for storing batch materials and separate batch preparation and storage areas, minimizing the usage of fine particles by humidification using alkali solutions or water and carrying out proper control operations in the furnace feed area.

The emission of sulfur oxides in the air can be controlled by reducing the quantity of sodium in the batch materials and also by using fuels containing low sulfur levels. Metals emitted in the sub-sectors can be controlled by using efficient dust abatement methods. The usage of efficient techniques to reduce the emission of greenhouse gases and treat waste water from industries will control and protect the environment from these pollutants. Glass is easily recyclable and must not be thrown into landfills as it degrades very slowly.

Recycling Process

Glass is a non-degradable material and can thus be recycled multiple number of times. Glass is one of those materials that can be very easily recycled. Glass is recycled through the following steps:

Broken glass is usually thrown away and this glass from the bin is taken to a glass treatment plant
It is separated based on its colors and the impurities are then removed from the glass
The glass now goes through the crushing and melting process that helps in creating a product called a ‘cullet’
The recycled glass is finally molded into the desired products
Molding does not take place if the recycled glass is used for decorative and manufacturing purposes
Glass products like glass bottles and jars are reused in shops.

Applications of Recycled Glass

Following are the applications of recycled glass:

For making landscaping material, decorative tiles, and new glass containers
As an aggregate in concrete and a flux agent in the manufacturing of brick
In the production of ceramic sanitary ware
The cullet made from recycled glass can be used for fiberglass, fluxes and frictionators
Mow-quality cullet is used in the manufacturing of driving safety reflective beads, roadbed aggregate and fiberglass insulation