Editorial Feature

Glass Recycling - An Introduction

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

Sources and Further Reading

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