(Smelter of the VOEST-Alpine, Austria)
Flashback: Metals are chemical elements displaying certain properties, notably metallic lustre, the capacity to lose electrons to become cationic (a positive ion), and the ability to conduct heat and electricity, by which it is normally distinguished from a non-metal. This group of materials comprises about two thirds of the known elements. Some elements, e.g. arsenic and antimony, exhibit both metallic and non-metallic properties, and are called metalloids. Metals are categorised in the periodic table according to their electron orbital arrangements which correspond in similar chemical properties. Such groups include the alkali metals (group Ia in the periodic table), the alkaline earth metals (group IIa), and the rare earth metals (lanthanide and actinide series). Most metals other than the alkali metals and the alkaline-earth metals are called transition metals. The oxidation states, or valence, of the metal ions vary from +1 for the alkali metals to +7 for some transition metals.
Chemically, the metals differ from the non-metals in that they form positive ions,
basic oxides and hydroxides. Upon exposure to moist air, a great many metals undergo corrosion, i.e.
enter into a chemical reaction, in that the oxygen of the atmosphere unites with the metal to form the
oxide of the metal, e.g. rust on exposed iron.
Al is not the only metal worth recycling; e.g. the nonferrous metal like Copper (Cu), or ordinary tins (usually made of steel) can contribute enormously when speaking about cutting energy costs and boosting efficiency. Ferromagnetic metals like steel and iron (Fe) can easily be separated from other dia- or paramegnetic materials. Non-magnetic materials require more sophisticated techniques to successfully separate them into their pure fractions.
Collection: With the available modern separation technologies, metal collection does not require to be split into its respective fraction at the collection site (Fe, Al, etc.). Though it has to be said that only those "household-metals" should be collected that are safe to use in the food industry (cans, foil, etc). These are more or less pure in their composition (no alloys and other compound materials) and therefore do not interfere with the smelting process).
Separation: Automated separation devices enable almost ideal separation efficiency. Powerful electromagnets separate the ferromagnetic fraction from the non-magnetic components, while high-frequency eddy current inducers enable separation of the para- and diamagnetic fractions.
Processing: The separated fractions are delivered to suitable smelters
where they are reprocessed to new materials. Being more or less pure, these materials do not require
energy-demanding extraction processes such as a blast-furnace. Mineral ore, on the other hand must
be processed in such a furnace in order to remove the impurities, which trap the metal oxides. In the
case of copper (Cu) for example, the blast furnace is chiefly used in smelting, i.e. extracting
metal from their ores by a series of induction steps. The basic principle is the reduction of the ores by
the action of carbon monoxide, i.e. the removal of oxygen from the metal oxide in order to obtain elemental
copper (aquisition of negative charges to obtain elemental Cu0). A blast furnace is kept
operational for as long as the internal insulating sheath protects the reaction chamber. Cu-ore treated
in a blast furnace yields a copper sulfide mixture, which requires further refined by electrolytic means.
Þ For final deposition, refer to the landfill section.
Metal processing (from left to right: iron, copper, aluminum)
References: Chang R. (1994); Chemistry 5th ed.; McGraw-Hill; New York - USA
For additional information visit one of the following web-sites
http://the Hall process
http://www.encyclopedia.com / periodic table