Recycling Issues in Materials Science and Engineering

One of the current environmental/economic/societal buzzwords is sustainability. In this context, sustainability represents the ability to maintain an acceptable lifestyle at the present level and into the indefinite future while preserving the environment. This means that over time and as populations increase in size, the Earth s resources must be used at a rate such that they can be replenished naturally and that emission levels of pollutants are maintained at acceptable levels. For engineers, this concept of sustainabihty translates into being responsible for the development of sustainable products. An internationally accepted standard, ISO 14001, has been established to help organizations comply with applicable laws and regulations and address the delicate balance between being profitable and reducing impacts on the environment.  

Most metal alloys (e.g., those with Fe or Cu), to one degree or another experience corrosion and are also biodegradable. However, some metals (e.g., Hg, Pb) are toxic and, when placed in landfills, may present health hazards. Furthermore, whereas alloys of most metals are recyclable, it is not feasible to recycle all alloys of every metal. In addition, the quality of alloys that are recycled tends to diminish with each cycle. 

Aluminum alloys are very corrosion resistant and, therefore, nonbiodegradable. Fortunately, however, they may be recycled in fact, aluminum is the most important recyclable nonferrous metal. Because aluminum is not easily corroded, it may be totally reclaimed. A low ratio of energy is required to refine recycled aluminum relative to its primary production. In addition, a large number of commercially available alloys have been designed to accommodate impurity contamination. The primary sources of recycled aluminum are used beverage cans and scrapped automobiles. 

The ceramic material consumed by the general public in the greatest quantities is glass, in the form of containers. Glass is a relatively inert material and, as such, does not decompose thus, it is not biodegradable. A significant proportion of municipal landfills consists of waste glass this is also true of incinerator residue. 

One reason that synthetic polymers (including rubber) are so popular as engineering materials is their chemical and biological inertness. On the down side, this characteristic is really a liability when it comes to waste disposal. Most polymers are not biodegradable and, therefore, do not biodegrade in landfills major sources of waste are from packaging. 

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