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Electrolysis of Molten Salts

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Refine or Recycle?
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Refine or Recycle?

             

Credit: Dave Dyet
Source: https://commons.wikimedia.org/wiki/File:Analcime_3_with_rock_Hydrous_sodium_aluminum_silicate_McGowan_Creek_Coberg_Hills_Lane_County_Oregon_2215.jpg
License: CC BY-NC 3.0

From this rock and others like it comes one of the most abundant metals known. Aluminum is found in many areas of the world and is used for food packaging and storage, components for vehicles, transmission of electricity, cooking utensils, and building materials, among others.

News You Can Use

  • Aluminum is the most abundant metal on earth and the third most abundant element overall. Because of its relative reactivity (aluminum ranks just below sodium and magnesium in the activity series), it does not exist free in nature. The most common form of aluminum in the ground is aluminum oxide (Al2O3), found as a mixture with ferric oxide in a deposit known as bauxite.
  • The aluminum in bauxite is extracted from other minerals by the Bayer method, a process that has changed little since its initial application in 1893. Sodium hydroxide converts the aluminum oxide to soluble aluminum hydroxide, leaving the iron oxide and other insoluble minerals behind. After separation, the aluminum hydroxide is converted back to its aluminum oxide form for refining. Roughly one ton of aluminum oxide can be obtained from two-three tons of bauxite.
  • The aluminum oxide then undergoes electrolytic reduction to produce metallic aluminum. The metal oxide is dissolved in molten sodium aluminum fluoride (cryolite) and an electric current is passed through the mixture. The solid aluminum metal settles to the bottom of the smelting container and is siphoned off. Large amounts of electricity are needed for this process, so a nearby power source is essential.
  • Credit: Emilian Robert Vicol
    Source: http://www.flickr.com/photos/free-stock/4999892549/
    License: CC BY-NC 3.0

    Although aluminum is a metal, it can be flattened into super thin sheets, which we refer to as aluminum foil [Figure2]

     

  • There are some significant environmental issues associated with aluminum refining. The solid residue from the Bayer process requires disposal of some sort, usually in a landfill. Some of the material has been used as an under layer for road construction. Fluoride products can contaminate the air and soil.
  • Watch a video at the link below to learn more about aluminum refining: https://www.youtube.com/watch?v=fa6KEwWY9HU

Show What You Know

Use the links below to learn more about aluminum production, then answer the following questions.

  1. Why is aluminum used in power transmission lines?
  2. What is the main purpose of the Bayer process?
  3. What is used to convert the aluminum oxide to a soluble material?
  4. What are the major reaction products of the Hall-Heroult process?
  5. How many barrels of oil would be needed to generate the electricity to replace all the aluminum cans in the U.S. that are not recycled in a year’s time?

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