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Dross is a mass
Mass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...

 of solid
Solid is one of the three classical states of matter . It is characterized by structural rigidity and resistance to changes of shape or volume. Unlike a liquid, a solid object does not flow to take on the shape of its container, nor does it expand to fill the entire volume available to it like a...

Impurities are substances inside a confined amount of liquid, gas, or solid, which differ from the chemical composition of the material or compound.Impurities are either naturally occurring or added during synthesis of a chemical or commercial product...

 floating on a molten metal. It appears usually on the melting of low-melting-point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

s or alloy
An alloy is a mixture or metallic solid solution composed of two or more elements. Complete solid solution alloys give single solid phase microstructure, while partial solutions give two or more phases that may or may not be homogeneous in distribution, depending on thermal history...

s such as tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...

, lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

, zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

 or aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, or by oxidation
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....

 of the metal(s). It can also consist of impurities such as paint leftovers. It can easily be skimmed off the surface before pouring the metal into a mold
Molding (process)
Molding or moulding is the process of manufacturing by shaping pliable raw material using a rigid frame or model called a pattern....

 or casting flask.

With tin and lead the dross can also be removed by adding sodium hydroxide pellets, which dissolve the oxides and form a slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...


Dross, as a solid, is distinguished from slag, which is a liquid. Dross product is not entirely waste material; aluminium dross, for example, can be recycled
Aluminium recycling
Aluminium recycling is the process by which scrap aluminium can be reused in products after its initial production. The process involves simply re-melting the metal, which is far less expensive and energy intensive than creating new aluminium through the electrolysis of aluminium oxide , which must...

 and is used in secondary steelmaking
Steelmaking is the second step in producing steel from iron ore. In this stage, impurities such as sulfur, phosphorus, and excess carbon are removed from the raw iron, and alloying elements such as manganese, nickel, chromium and vanadium are added to produce the exact steel required.-Older...

 for slag deoxidation
A deoxidizer is a chemical used in a reaction or process to remove oxygen. In comparison with antioxidants, deoxidizers are not used for stabilization during storage but for oxygen removal during manufacture...


Etymology and usage

The term dross derives from the Old English word dros, meaning the scum produced when smelting metals. By the 15th Century it had come to refer to rubbish in general. Dregs and the geological term druse
Druse (geology)
In geological usage druse or druzy is a coating of fine crystals on a rock fracture surface, vein or within a vug or geode.- Occurrence :Druse occurs worldwide, the most common is perhaps quartz druse within voids in chert or agates...

 are also thought to be etymologically related. Metallurgical dross is referenced as a metaphor for worthless material in the Bible and in other religious texts.

External links

  • AZoM.com – Aluminium Dross Recycling
  • Herbert F. Lund. The McGraw-Hill recycling handbook. Chapter 37.23: United Kingdom
    United Kingdom
    The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

    : European Union
    European Union
    The European Union is an economic and political union of 27 independent member states which are located primarily in Europe. The EU traces its origins from the European Coal and Steel Community and the European Economic Community , formed by six countries in 1958...

     Directive Percipitates Aluminum "Dross" Recycling
    Recycling is processing used materials into new products to prevent waste of potentially useful materials, reduce the consumption of fresh raw materials, reduce energy usage, reduce air pollution and water pollution by reducing the need for "conventional" waste disposal, and lower greenhouse...

  • Residues from aluminium dross recycling in cement
  • DrosRite Aluminum Recycling Process