Editing Thallium (section)

==Occurrence and production==
Thallium [[Abundance of elements in Earth's crust | concentration in the Earth's crust]] is estimated to be 0.7&nbsp;mg/kg,<ref name="USGS-CS2010">{{cite web|first = David E.|last = Guberman|title = Mineral Commodity Summaries 2010: Thallium|url = http://minerals.usgs.gov/minerals/pubs/commodity/thallium/mcs-2010-thall.pdf|access-date = 2010-05-13|publisher = United States Geological Survey|archive-date = 2010-07-15|archive-url = https://web.archive.org/web/20100715162053/http://minerals.usgs.gov/minerals/pubs/commodity/thallium/mcs-2010-thall.pdf|url-status = live}}</ref> mostly in association with [[potassium]]-based [[mineral]]s in [[clay]]s, [[soil]]s, and [[granite]]s. The major source of thallium for practical purposes is the trace amount that is found in [[copper]], [[lead]], [[zinc]], and other heavy-metal-[[sulfide]] [[ore]]s.<ref>{{Cite journal| doi = 10.1007/BF01684859| title = Thallium: Occurrence in the environment and toxicity to fish| year = 1975| last1 = Zitko | first1 = V.| last2 = Carson | first2 = W. V.| last3 = Carson | first3 = W. G.| journal = Bulletin of Environmental Contamination and Toxicology| volume = 13| pages = 23–30| pmid = 1131433| issue = 1| bibcode = 1975BuECT..13...23Z| s2cid = 40955658}}</ref><ref name="Vira">{{cite journal|doi = 10.1016/j.envint.2004.09.003|title = Thallium: a review of public health and environmental concerns|date = 2005|last1 = Peter|first1 = A.|last2 = Viraraghavan|first2 = T.|journal = [[Environment International]]|volume = 31|pages = 493–501|pmid = 15788190|issue = 4| bibcode=2005EnInt..31..493P }}</ref>

[[File:Hutchinsonite-131710.jpg|thumb|left|alt=A close view of a rock crusted with groups of glassy, lustrous, silvery-blue [[hutchinsonite]], in tight clusters of loosely aligned needle-like crystals, among smaller clusters of tiny orange-brown crystals|Crystals of [[hutchinsonite]] ((Tl,Pb)<sub>2</sub>As<sub>5</sub>S<sub>9</sub>)]]
Thallium is found in the minerals [[crookesite]] TlCu<sub>7</sub>Se<sub>4</sub>, [[hutchinsonite]] TlPbAs<sub>5</sub>S<sub>9</sub>, and [[lorándite]] TlAsS<sub>2</sub>.<ref>{{cite journal|doi = 10.1016/0016-7037(52)90003-3|title = The geochemistry of thallium|date = 1952|last1 = Shaw|first1 = D.|journal = Geochimica et Cosmochimica Acta|volume = 2|issue = 2|pages = 118–154 |bibcode = 1952GeCoA...2..118S }}</ref> Thallium also occurs as a trace element in [[iron pyrite]], and thallium is extracted as a by-product of roasting this mineral for the production of [[sulfuric acid]].<ref name="sl2001">{{cite web|title=Chemical fact sheet&nbsp;– Thallium|publisher=Spectrum Laboratories|date=April 2001|url=http://www.speclab.com/elements/thallium.htm|access-date=2008-02-02|archive-date=2008-02-21|archive-url=https://web.archive.org/web/20080221222321/http://www.speclab.com/elements/thallium.htm|url-status=dead}}</ref><ref name="Downs">{{cite book|title = Chemistry of aluminium, gallium, indium, and thallium|first = Anthony John|last = Downs|publisher = Springer|date = 1993|isbn = 978-0-7514-0103-5|pages = 90 and 106|url = https://books.google.com/books?id=v-04Kn758yIC|access-date = 2016-09-26|archive-date = 2017-02-22|archive-url = https://web.archive.org/web/20170222131541/https://books.google.com/books?id=v-04Kn758yIC|url-status = live}}</ref>

Thallium can also be obtained from the [[smelting]] of lead and zinc ores. [[Manganese nodule]]s found on the [[ocean floor]] contain some thallium.<ref>{{cite journal|doi = 10.1016/j.marchem.2003.09.006|pages = 125–139|title = The mass balance of dissolved thallium in the oceans|date = 2004|issue = 3–4|last1 = Rehkamper|first1 = M.|journal = Marine Chemistry|volume = 85|last2 = Nielsen|first2 = Sune G.| bibcode=2004MarCh..85..125R }}</ref> In addition, several other thallium minerals, containing 16% to 60% thallium, occur in nature as complexes of sulfides or selenides that primarily contain [[antimony]], [[arsenic]], copper, lead, and [[silver]]. These minerals are rare, and have had no commercial importance as sources of thallium.<ref name="USGS-CS2010" /> The [[Allchar deposit]] in southern [[North Macedonia]] was the only area where thallium was actively mined. This deposit still contains an estimated 500&nbsp;tonnes of thallium, and it is a source for several rare thallium minerals, for example lorándite.<ref>{{cite journal|doi = 10.1016/0168-9002(88)90170-2|title = The Allchar Tl–As–Sb deposit, Yugoslavia and its specific metallogenic features|date = 1988|last1 = Jankovic|first1 = S.|journal = Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment|volume = 271|issue = 2|page = 286|bibcode = 1988NIMPA.271..286J }}</ref><!-- The "Alshar" epithermal Au-As-Sb-Tl deposit, located in southern Macedonia, is the only larger mining area 10.1134/S1075701506030020 https://www.jstor.org/pss/2843882 -->

The [[United States Geological Survey]] (USGS) estimates that the annual worldwide production of thallium is 10&nbsp;metric tonnes as a by-product from the smelting of copper, zinc, and lead ores.<ref name="USGS-CS2010" /> Thallium is either extracted from the dusts from the smelter flues or from residues such as [[slag]] that are collected at the end of the smelting process.<ref name="USGS-CS2010" /> The raw materials used for thallium production contain large amounts of other materials and therefore a purification is the first step. The thallium is leached either by the use of an alkali or sulfuric acid from the material. The thallium is precipitated several times from the solution to remove impurities. At the end it is converted to thallium sulfate and the thallium is extracted by [[electrolysis]] on [[platinum]] or [[stainless steel]] plates.<ref name="Downs" /> The production of thallium decreased by about 33% in the period from 1995 to 2009 – from about 15&nbsp;metric [[tonne]]s to about 10&nbsp;tonnes. Since there are several small deposits or ores with relatively high thallium content, it would be possible to increase the production if a new application, such as a thallium-containing [[high-temperature superconductivity|high-temperature superconductor]], becomes practical for widespread use outside of the laboratory.<ref>{{cite web|first = Gerald R.|last = Smith|title = Mineral commodity summaries 1996: Thallium|url = http://minerals.usgs.gov/minerals/pubs/commodity/thallium/thallmcs96.pdf|access-date = 2010-05-13|publisher = United States Geological Survey|archive-date = 2010-05-29|archive-url = https://web.archive.org/web/20100529192216/http://minerals.usgs.gov/minerals/pubs/commodity/thallium/thallmcs96.pdf|url-status = live}}</ref>