From Wikipedia, the free encyclopedia - View original article
In metallurgy, a non-ferrous metal is any metal that is not ferrous, including alloys, that does not contain iron in appreciable amounts. Generally more expensive than ferrous metals, non-ferrous metals are used because of desirable properties such as low weight (e.g., aluminium), higher conductivity (e.g., copper), non-magnetic property or resistance to corrosion (e.g., zinc). Some non-ferrous materials are also used in the iron and steel industries. For example, bauxite is used as flux for blast furnaces, while others such as wolframite, pyrolusite and chromite are used in making ferrous alloys.
Important non-ferrous metals include aluminium, copper, lead, nickel, tin, titanium and zinc, and alloys such as brass. Precious metals such as gold, silver and platinum and exotic or rare metals such as cobalt, mercury, tungsten, arsenic, beryllium, bismuth, cerium, cadmium, niobium, indium, gallium, germanium, lithium, selenium, tantalum, tellurium, vanadium, and zirconium are also non-ferrous. They are usually obtained through minerals such as sulfides, carbonates, and silicates. Non-ferrous metals are usually refined through electrolysis.
Due to its extensive use, non-ferrous scrap metal is usually recycled. The secondary materials in scrap are vital to the metallurgy industry, as the production of new metals often needs them. Some recycling facilities resmelt and recast non-ferrous materials; the dross is collected and stored onsite while the metal fumes are filtered and collected. Non-ferrous scrap metals are sourced from industrial scrap materials, particle emissions and obsolete technology (for example, copper cables) scrap. Precious non-ferrous materials are usually sourced from jewellery, electronics and used industrial catalysts. Recycling non-ferrous materials can pose hazards due to exposure. Skin disorders, respiratory problems and poisoning have been reported as health hazards.
Extraction and use of non-ferrous materials pollutes the environment. Though the pollution agents vary for each non-ferrous metal (like red mud for aluminium), they often include sulfur dioxide, particulates and various constituents such as fluorides. Sulfur dioxide is a known problem as most non-ferrous metals are extracted from sulfide ores. They can be recovered in high amounts and be sold as liquid sulfur oxide or sulfuric acid. Submicron metallic particulates are released in every aspect of the production of non-ferrous metals. These particulates may be removed through baghouses, electrostatic precipitators and drop scrubbers. Constituents such as fluorides vary from smelter to smelter and can be recovered or removed through special processes.
Non-ferrous metals were the first metals used by humans for metallurgy. Gold, silver and copper existed in their native crystalline yet metallic form. These crystals, though rare, are enough to attract the attention of humans. Less susceptible to oxygen than most other metals, they can be found even in weathered outcroppings. Copper was the first metal to be forged; it was soft enough to be fashioned into various objects by cold forging, and it could be melted in a crucible. Gold, silver and copper replaced some of the functions of other resources, such as wood and stone, owing to their ability to be shaped into various forms for different uses. Due to their rarity, these gold, silver and copper artifacts were treated as luxury items and handled with great care. The use of copper also heralded the transition from the Stone Age to the Copper Age. The Bronze Age, which succeeded the Copper Age, was again heralded by the invention of bronze, an alloy of copper with the non-ferrous metal tin.