Editing Metal (section)

==Lifecycle==
===Formation===
{{See also|Nucleosynthesis}}
{{Periodic table (metal abundance in Earth crust)}}

Metallic elements up to the [[iron peak|vicinity of iron]] (in the periodic table) are largely made via [[stellar nucleosynthesis]]. In this process, lighter elements from hydrogen to [[silicon]] undergo successive [[nuclear fusion|fusion]] reactions inside stars, releasing light and heat and forming heavier elements with higher atomic numbers.<ref name="Cox">{{harvnb|Cox|1997|pp=73–89}}</ref>

Heavier elements are not usually formed this way since fusion reactions involving such nuclei would consume rather than release energy.<ref>{{harvnb|Cox|1997|pp=32, 63, 85}}</ref> Rather, they are largely synthesised (from elements with a lower atomic number) by [[neutron capture]], with the two main modes of this repetitive capture being the [[s-process]] and the [[r-process]]. In the s-process ("s" stands for "slow"), singular captures are separated by years or decades, allowing the less stable nuclei to [[beta decay]],<ref>{{harvnb|Podosek|2011|p=482}}</ref> while in the r-process ("rapid"), captures happen faster than nuclei can decay. Therefore the s-process takes a more-or-less clear path: for example, stable cadmium-110 nuclei are successively bombarded by free neutrons inside a star until they form cadmium-115 nuclei which are unstable and decay to form indium-115 (which is nearly stable, with a half-life {{val|30000}} times the age of the universe). These nuclei capture neutrons and form indium-116, which is unstable, and decays to form tin-116, and so on.<ref name="Cox" /><ref>{{harvnb|Padmanabhan|2001|p=234}}</ref>{{#tag:ref|In some cases, for example in the presence of [[photodisintegration|high energy gamma rays]] or in a [[rp-process|very high temperature hydrogen rich environment]], the subject nuclei may experience neutron loss or proton gain resulting in the production of (comparatively rare) [[p-nuclei|neutron deficient isotopes]].<ref>{{harvnb|Rehder|2010|pp=32, 33}}</ref>|group=n}} In contrast, there is no such path in the r-process. The s-process stops at bismuth due to the short half-lives of the next two elements, polonium and astatine, which decay to bismuth or lead. The r-process is so fast it can skip this zone of instability and go on to create heavier elements such as [[thorium]] and uranium.<ref>{{harvnb|Hofmann|2002|pp=23–24}}</ref>

Metals condense in planets as a result of stellar evolution and destruction processes. Stars lose much of their mass when it is [[stellar mass loss|ejected]] late in their lifetimes, and sometimes thereafter as a result of a [[neutron star]] merger,<ref>{{harvnb|Hadhazy|2016}}</ref>{{#tag:ref|The ejection of matter when two neutron stars collide is attributed to the interaction of their [[tidal force]]s, possible crustal disruption, and shock heating (which is what happens if you floor the accelerator in car when the engine is cold).<ref>{{harvnb|Choptuik|Lehner|Pretorias|2015|p=383}}</ref>|group=n}} thereby increasing the abundance of elements heavier than helium in the [[interstellar medium]]. When gravitational attraction causes this matter to coalesce and collapse [[nebular hypothesis|new stars and planets are formed]].<ref>{{harvnb|Cox|1997|pp=83, 91, 102–103}}</ref>

===Abundance and occurrence===
{{See also|Abundance of the chemical elements}}
[[File:Diaspore-Margarite-rare-09-05b.jpg|thumb|left|A sample of [[diaspore]], an aluminium oxide hydroxide mineral, α-AlO(OH)|alt=A sample of diaspore]]
The [[Earth's crust]] is made of approximately 25% of metallic elements by weight, of which 80% are light metals such as sodium, magnesium, and aluminium. Despite the overall scarcity of some heavier metals such as copper, they can become concentrated in economically extractable quantities as a result of mountain building, erosion, or other geological processes.

Metallic elements are primarily found as lithophiles (rock-loving) or chalcophiles (ore-loving). Lithophile elements are mainly the s-block elements, the more reactive of the d-block elements, and the f-block elements. They have a strong affinity for oxygen and mostly exist as relatively low-density silicate minerals. Chalcophile elements are mainly the less reactive d-block elements, and the period 4–6 p-block metals. They are usually found in (insoluble) sulfide minerals. Being denser than the lithophiles, hence sinking lower into the crust at the time of its solidification, the chalcophiles tend to be less abundant than the lithophiles.

On the other hand, gold is a siderophile, or iron-loving element. It does not readily form compounds with either oxygen or sulfur. At the time of the Earth's formation, and as the most noble (inert) of metallic elements, gold sank into the core due to its tendency to form high-density metallic alloys. Consequently, it is relatively rare. Some other (less) noble ones—molybdenum, rhenium, the platinum group metals (ruthenium, rhodium, palladium, osmium, iridium, and platinum), germanium, and tin—can be counted as siderophiles but only in terms of their primary occurrence in the Earth (core, mantle, and crust), rather the crust. These otherwise occur in the crust, in small quantities, chiefly as chalcophiles (less so in their native form).{{#tag:ref|Iron, cobalt, nickel, and tin are also siderophiles from a whole of Earth perspective.|group=n}}

The rotating fluid outer core of the Earth's interior, which is composed mostly of iron, is thought to be the source of Earth's protective magnetic field.{{#tag:ref|Another life-enabling role for iron is as a key constituent of [[hemoglobin]], which enables the transportation of oxygen from the lungs to the rest of the body.|group=n}} The core lies above Earth's solid inner core and below its mantle. If it could be rearranged into a column having a {{cvt|5|m2}} footprint it would have a height of nearly 700 light years. The magnetic field shields the Earth from the charged particles of the solar wind, and cosmic rays that would otherwise strip away the upper atmosphere (including the ozone layer that limits the transmission of ultraviolet radiation).

===Extraction===
{{main|Ore|Mining|Extractive metallurgy}}
Metallic elements are often extracted from the Earth by mining ores that are rich sources of the requisite elements, such as [[bauxite]]. Ores are located by [[prospecting]] techniques, followed by the exploration and examination of deposits. Mineral sources are generally divided into [[surface mining|surface mines]], which are mined by excavation using heavy equipment, and [[underground mining (hard rock)|subsurface mines]]. In some cases, the sale price of the metal(s) involved make it economically feasible to mine lower concentration sources.

Once the ore is mined, the elements must be [[extractive metallurgy|extracted]], usually by chemical or electrolytic reduction. [[Pyrometallurgy]] uses high temperatures to convert ore into raw metals, while [[hydrometallurgy]] employs [[aqueous]] chemistry for the same purpose.

When a metallic ore is an ionic compound, the ore must usually be [[smelting|smelted]]—heated with a reducing agent—to extract the pure metal. Many common metals, such as iron, are smelted using [[carbon]] as a reducing agent. Some metals, such as aluminium and [[sodium]], have no commercially practical reducing agent, and are extracted using [[electrolysis]] instead.<ref name="losal">{{cite web |url=https://periodic.lanl.gov/11.shtml |title=Los Alamos National Laboratory – Sodium |access-date=2007-06-08}}</ref><ref>{{cite web |url=https://periodic.lanl.gov/13.shtml |title=Los Alamos National Laboratory – Aluminum |access-date=2007-06-08}}</ref>

[[Sulfide]] ores are not reduced directly to the metal but are roasted in air to convert them to oxides.

===Recycling===
[[File:CompactedSteelScraps.jpg|thumb|left|A pile of compacted steel scraps, ready for recycling|alt=A pile of compacted steel scraps]]
Demand for metals is closely linked to economic growth given their use in infrastructure, construction, manufacturing, and consumer goods. During the 20th century, the variety of metals used in society grew rapidly. Today, the development of major nations, such as China and India, and technological advances, are fueling ever more demand. The result is that mining activities are expanding, and more and more of the world's metal stocks are above ground in use, rather than below ground as unused reserves. An example is the in-use stock of [[copper]]. Between 1932 and 1999, copper in use in the U.S. rose from 73 g to 238 g per person.<ref name="unep.org">[http://www.unep.org/resourcepanel/Publications/tabid/54044/Default.aspx ''The Recycling Rates of Metals: A Status Report''] {{webarchive|url=https://web.archive.org/web/20160101194304/http://www.unep.org/resourcepanel/Publications/tabid/54044/Default.aspx |date=2016-01-01}} 2010, [[International Resource Panel]], [[United Nations Environment Programme]]</ref>

Metals are inherently recyclable, so in principle, can be used over and over again, minimizing these negative environmental impacts and saving energy. For example, 95% of the energy used to make aluminium from bauxite ore is saved by using recycled material.<ref>[https://www.theguardian.com/environment/2008/feb/22/pledges.waste ''Tread lightly: Aluminium attack''] Carolyn Fry, Guardian.co.uk, 22 February 2008.</ref>

Globally, metal recycling is generally low. In 2010, the [[International Resource Panel]], hosted by the [[United Nations Environment Programme]] published reports on metal stocks that exist within society<ref>[http://www.unep.org/resourcepanel/Publications/tabid/54044/Default.aspx ''Metal Stocks in Society: Scientific Synthesis''] {{webarchive|url=https://web.archive.org/web/20160101194304/http://www.unep.org/resourcepanel/Publications/tabid/54044/Default.aspx |date=2016-01-01}} 2010, [[International Resource Panel]], [[United Nations Environment Programme]]</ref> and their recycling rates.<ref name="unep.org"/> The authors of the report observed that the metal stocks in society can serve as huge mines above ground. They warned that the recycling rates of some rare metals used in applications such as mobile phones, battery packs for hybrid cars and fuel cells are so low that unless future end-of-life recycling rates are dramatically stepped up these critical metals will become unavailable for use in modern technology.