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In the 1970s, increasing environmental awareness renewed interest in recycling. Today, about 32% of the average 1,643 pounds of waste produced annually per person in the United States is recycled. Significantly less municipal waste is being dumped in our dwindling landfills. Chemical engineers have played a key role in building the post-consumer and industrial waste recycling industry.

Any successful recycling program must have three basic qualities

• A suitable collection infrastructure,
• Appropriate reprocessing techniques to convert the waste into suitable end products, and
• A need or a market for the recycled products.

Recycling aluminum

Chemical engineers and metallurgists have worked together for decades to perfect metal recycling techniques. Sometimes it is easy. For instance, stainless-steel cans can often be recycled directly back into the steel mill feed stream with little or no prior processing. Recycling aluminum, however, is more challenging.

The process for recycling aluminum was developed by chemical engineers in the 1960s, and aluminum is now one of the most widely recycled materials. Almost two-thirds of the aluminum cans in the United States are recycled, and 85% to 90% of the aluminum in cars is recycled.

Before aluminum is reused, all lacquer, paint, and labels are removed in a heated oven. Cans are then chopped into small pieces and added to a molten aluminum bath along with chemicals to remove any impurities. The remaining aluminum is formed into ingots for reuse by fabricators.

The widespread use of recycled aluminum saves energy and reduces pollution, because mining and processing raw bauxite ore to extract the aluminum it contains is very energy and waste intensive. Specifically,

• Each one ton of aluminum cans produced from recycled cans saves five tons of bauxite;
• The reuse of aluminum cans reduces air pollution by 99% and energy consumption by 95% compared with the production of virgin aluminum from bauxite; and
• The 54 billion cans that the United States recycled in 2006 saved the equivalent of 15 billion barrels of crude oil.

Recycling paper

Paper is another post-consumer product that is now routinely recycled. Because paper mills cannot use recycled paper as a direct substitute for virgin tree pulp, chemical engineers have devised and optimized processes that involve

• Blending recycled paper and water to produce a pulp slurry,
• Removing all inks and other performance chemicals in the paper, and
• Filtering the slurry to remove solid impurities.

One of the biggest technical hurdles chemical engineers had to overcome was the fact that recycled pulp has shorter fibers than virgin pulp. This characteristic makes the finished paper weaker and less attractive. By combining virgin pulp (typically from wood chips) with recycled pulp, chemical engineers solved the problem with a processing technique that produces newsprint and other recycled-paper products that meet all strength and aesthetic requirements.

Today, more than 70% of the newsprint in the United States is collected for reuse, significantly reducing both the disposal burden on landfills and the environmental costs of harvesting virgin wood.

Recycling plastics

Because plastics are used in so many aspects of our daily lives, they represent an ever-growing part of the nation's waste stream. In landfills they present a particular problem, as they do not degrade readily. In addition, significant amounts of crude oil and energy are used in producing plastics.

We can now recycle most plastics into useful products. Because of chemical-engineering innovations, plastics are separated by machine and reprocessed without significant material breakdown, enabling reuse of many such plastic products as pipe, toys, and decorations. This process not only protects our environment from plastic litter but also helps the United States become more energy independent.

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