Editing Group 7 element (section)

== Occurrence and production ==

=== Manganese ===
{{Main article|Manganese#Production}}

Manganese comprises about 1000&nbsp;[[Parts per million|ppm]]&nbsp;(0.1%) of the [[Earth's crust]] and is the [[Abundance of elements in Earth's crust|12th most abundant element]].<ref name="Emsley2001">{{harvnb|Emsley|2001|pp=[https://archive.org/details/naturesbuildingb0000emsl/page/249 249–253]}}</ref> Soil contains 7–9000&nbsp;ppm of manganese with an average of 440&nbsp;ppm.<ref name="Emsley2001" /> The&nbsp;atmosphere contains 0.01&nbsp;μg/m<sup>3</sup>.<ref name="Emsley2001" /> Manganese occurs principally as [[pyrolusite]] ([[manganese(IV) oxide|MnO<sub>2</sub>]]), [[braunite]] (Mn<sup>2+</sup>Mn<sup>3+</sup><sub>6</sub>)(SiO<sub>12</sub>),<ref>{{cite journal|pages=65–71 |journal=Contributions to Mineralogy and Petrology|title=Geochemistry of braunite and associated phases in metamorphosed non-calcareous manganese ores of India|first=P. K.|last=Bhattacharyya|author2=Dasgupta, Somnath |author3=Fukuoka, M. |author4=Roy Supriya |doi=10.1007/BF00371403|date=1984|volume=87|issue=1|bibcode=1984CoMP...87...65B|s2cid=129495326}}</ref> [[psilomelane]] {{chem2|(Ba,H2O)2Mn5O10}}, and to a lesser extent as [[rhodochrosite]] ([[manganese(II) carbonate|MnCO<sub>3</sub>]]).

[[File:World Manganese Production 2006.svg|thumb|upright=1.6|Percentage of manganese output in 2006 by countries<ref name="USGSMCS2009">USGS Mineral Commodity Summaries 2009</ref>]]

The most important manganese ore is pyrolusite ([[manganese(IV) oxide|MnO<sub>2</sub>]]). Other economically important manganese ores usually show a close spatial relation to the iron ores, such as [[sphalerite]].<ref name="Holl">{{cite book|publisher=Walter de Gruyter|date=1985|edition=91–100 |pages=1110–1117|isbn=978-3-11-007511-3|title=Lehrbuch der Anorganischen Chemie|first=Arnold F.|last=Holleman|author2=Wiberg, Egon|author3=Wiberg, Nils|language=de|chapter=Mangan}}</ref><ref>{{Cite journal|last1=Cook|first1=Nigel J.|last2=Ciobanu|first2=Cristiana L.|last3=Pring|first3=Allan|last4=Skinner|first4=William|last5=Shimizu|first5=Masaaki|last6=Danyushevsky|first6=Leonid|last7=Saini-Eidukat|first7=Bernhardt|last8=Melcher|first8=Frank|date=2009|title=Trace and minor elements in sphalerite: A LA-ICPMS study|url=https://linkinghub.elsevier.com/retrieve/pii/S0016703709003263|journal=Geochimica et Cosmochimica Acta|language=en|volume=73|issue=16|pages=4761–4791|doi=10.1016/j.gca.2009.05.045|bibcode=2009GeCoA..73.4761C|url-access=subscription}}</ref> Land-based resources are large but irregularly distributed. About 80% of the known world manganese resources are in South Africa; other important manganese deposits are in Ukraine, Australia, India, China, [[Gabon]] and Brazil.<ref name="USGSMCS2009" /> According to 1978 estimate, the [[ocean floor]] has 500 billion tons of [[manganese nodule]]s.<ref>{{cite journal|doi=10.1016/j.micron.2008.10.005|pages=350–358|date=2009|title=Manganese/polymetallic nodules: micro-structural characterization of exolithobiontic- and endolithobiontic microbial biofilms by scanning electron microscopy|volume=40 |issue=3|pmid=19027306|journal=Micron |author1=Wang, X|author2=Schröder, HC|author3=Wiens, M|author4=Schlossmacher, U|author5=Müller, WEG}}</ref> Attempts to find economically viable methods of harvesting manganese nodules were abandoned in the 1970s.<ref>{{cite journal |title=Manganese Nodules: Dimensions and Perspectives |journal=Marine Geology |volume=41 |issue=3–4 |pages=343|publisher=Springer |date=1978 |isbn=978-90-277-0500-6 |author=United Nations Ocean Economics and Technology Office, Technology Branch, United Nations |bibcode=1981MGeol..41..343C |doi=10.1016/0025-3227(81)90092-X}}</ref>

In South Africa, most identified deposits are located near [[Hotazel]] in the [[Northern Cape Province]], with a 2011 estimate of 15 billion tons. In 2011 South Africa produced 3.4 million tons, topping all other nations.<ref name="Mbendi">{{cite web |url=http://www.mbendi.com/indy/ming/mang/af/sa/p0005.htm |title=Manganese Mining in South Africa – Overview |publisher=MBendi.com |access-date=4 January 2014 |url-status=dead |archive-url=https://web.archive.org/web/20160205194737/http://www.mbendi.com/indy/ming/mang/af/sa/p0005.htm |archive-date=5 February 2016 }}</ref>

Manganese is mainly mined in South Africa, Australia, China, Gabon, Brazil, India, Kazakhstan, Ghana, Ukraine and Malaysia.<ref>{{Cite journal|doi = 10.1007/s11837-018-2769-4|title = Review of Manganese Processing for Production of TRIP/TWIP Steels, Part 1: Current Practice and Processing Fundamentals|journal = JOM |volume = 70|issue = 5|pages = 680–690|year = 2018|last1 = Elliott|first1 = R|last2 = Coley|first2 = K|last3 = Mostaghel|first3 = S|last4 = Barati|first4 = M|bibcode = 2018JOM....70e.680E|s2cid = 139950857}}</ref>

For the production of [[ferromanganese]], the manganese ore is mixed with iron ore and carbon, and then reduced either in a blast furnace or in an electric arc furnace.<ref name="IndMin">{{cite book|title=Industrial Minerals & Rocks: Commodities, Markets, and Uses |edition=7th|publisher=SME|date=2006|isbn=978-0-87335-233-8|chapter=Manganese|first=L. A.|last=Corathers |author2=Machamer, J. F. |chapter-url=https://books.google.com/books?id=zNicdkuulE4C&pg=PA631|pages=631–636}}</ref> The resulting [[ferromanganese]] has a manganese content of 30 to 80%.<ref name="Holl" /> Pure manganese used for the production of iron-free alloys is produced by [[Leaching (metallurgy)|leaching]] manganese ore with [[sulfuric acid]] and a subsequent [[electrowinning]] process.<ref name="hydrometI">{{cite journal|doi=10.1016/j.hydromet.2007.08.010 |title=Manganese metallurgy review. Part I: Leaching of ores/secondary materials and recovery of electrolytic/chemical manganese dioxide|date=2007|last=Zhang|first=Wensheng|author2=Cheng, Chu Yong|journal=Hydrometallurgy|volume=89 |pages=137–159|issue=3–4|bibcode=2007HydMe..89..137Z }}</ref>

[[File:Manganese Process Flow Diagram.jpg|left|thumb|upright=1.3|alt=Contains reactions and temperatures, as well as showing advanced processes such as the heat exchanger and milling process.|Process flow diagram for a manganese refining circuit.]]
A more progressive extraction process involves directly reducing (a low grade) manganese ore in a heap leach. This is done by [[Percolation|percolating]] natural gas through the bottom of the heap; the natural gas provides the heat (needs to be at least 850&nbsp;°C) and the reducing agent (carbon monoxide). This reduces all of the manganese ore to manganese oxide (MnO), which is a leachable form. The ore then travels through a [[Mill (grinding)|grinding]] circuit to reduce the particle size of the ore to between 150 and 250 μm, increasing the surface area to aid leaching. The ore is then added to a leach tank of [[sulfuric acid]] and [[Iron(II)|ferrous iron]] (Fe<sup>2+</sup>) in a 1.6:1 ratio. The iron reacts with the [[manganese dioxide]] (MnO<sub>2</sub>) to form [[iron(III) oxide-hydroxide]] (FeO(OH)) and elemental manganese (Mn):

This process yields approximately 92% recovery of the manganese. For further purification, the manganese can then be sent to an electrowinning facility.<ref name="ManganeseRecovery">{{cite web|url=http://www.americanmanganeseinc.com/wp-content/uploads/2011/08/American-Manganese-Phase-II-August-19-2010-Final-Report-Internet-Version-V2.pdf|title=The Recovery of Manganese from low grade resources: bench scale metallurgical test program completed|date=2010|author=Chow, Norman|author2=Nacu, Anca|author3=Warkentin, Doug|author4=Aksenov, Igor|author5=Teh, Hoe|name-list-style=amp|publisher=Kemetco Research Inc.|url-status=dead|archive-url=https://web.archive.org/web/20120202065633/http://www.americanmanganeseinc.com/wp-content/uploads/2011/08/American-Manganese-Phase-II-August-19-2010-Final-Report-Internet-Version-V2.pdf|archive-date=2 February 2012}}</ref>

In 1972 the [[Central Intelligence Agency|CIA]]'s [[Project Azorian]], through billionaire [[Howard Hughes]], commissioned the ship ''[[Hughes Glomar Explorer]]'' with the cover story of harvesting manganese nodules from the sea floor.<ref>{{Cite news|url=https://www.bbc.com/news/science-environment-42994812|title=The CIA secret on the ocean floor|date=19 February 2018|work=BBC News|access-date=3 May 2018|language=en-GB}}</ref> That triggered a rush of activity to collect manganese nodules, which was not actually practical. The real mission of ''Hughes Glomar Explorer'' was to raise a sunken [[Union of Soviet Socialist Republics|Soviet]] submarine, the [[Soviet submarine K-129 (1960)|K-129]], with the goal of retrieving Soviet code books.<ref name="azorian">{{cite web |url=http://www2.gwu.edu/~nsarchiv/nukevault/ebb305/index.htm |title=Project Azorian: The CIA's Declassified History of the Glomar Explorer |publisher=National Security Archive at George Washington University |date=12 February 2010 |access-date=18 September 2013}}</ref>

An abundant resource of manganese in the form of [[Manganese nodule|Mn nodules]] found on the ocean floor.<ref>{{cite book |last1=Hein |first1=James R. |title=Encyclopedia of Marine Geosciences - Manganese Nodules |date=January 2016 |publisher=Springer |pages=408–412 |url=https://www.researchgate.net/publication/306107551 |access-date=2 February 2021}}</ref><ref>{{cite journal |last1=Hoseinpour |first1=Vahid |last2=Ghaemi |first2=Nasser |title=Green synthesis of manganese nanoparticles: Applications and future perspective–A review |journal=Journal of Photochemistry and Photobiology B: Biology |date=1 December 2018 |volume=189 |pages=234–243 |doi=10.1016/j.jphotobiol.2018.10.022 |pmid=30412855 |bibcode=2018JPPB..189..234H |s2cid=53248245 |url=https://www.sciencedirect.com/science/article/abs/pii/S101113441830959X |access-date=2 February 2021|url-access=subscription }}</ref> These nodules, which are composed of 29% manganese,<ref>{{cite web |last1=International Seabed Authority |title=Polymetallic Nodules |url=https://isa.org.jm/files/files/documents/eng7.pdf |website=isa.org |publisher=International Seabed Authority |access-date=2 February 2021 |archive-date=23 October 2021 |archive-url=https://web.archive.org/web/20211023145629/https://isa.org.jm/files/files/documents/eng7.pdf |url-status=dead }}</ref> are located along the [[seabed|ocean floor]] and the potential impact of mining these nodules is being researched. Physical, chemical, and biological environmental impacts can occur due to this nodule mining disturbing the seafloor and causing sediment plumes to form. This suspension includes metals and inorganic nutrients, which can lead to contamination of the near-bottom waters from dissolved toxic compounds. Mn nodules are also the grazing grounds, living space, and protection for endo- and epifaunal systems. When theses nodules are removed, these systems are directly affected. Overall, this can cause species to leave the area or completely die off.<ref>{{Cite journal|last1=Oebius|first1=Horst U|last2=Becker|first2=Hermann J|last3=Rolinski|first3=Susanne|last4=Jankowski|first4=Jacek A|date=January 2001|title=Parametrization and evaluation of marine environmental impacts produced by deep-sea manganese nodule mining|url=http://dx.doi.org/10.1016/s0967-0645(01)00052-2|journal=Deep Sea Research Part II: Topical Studies in Oceanography|volume=48|issue=17–18|pages=3453–3467|doi=10.1016/s0967-0645(01)00052-2|bibcode=2001DSRII..48.3453O|issn=0967-0645|url-access=subscription}}</ref> Prior to the commencement of the mining itself, research is being conducted by [[United Nations]] affiliated bodies and state-sponsored companies in an attempt to fully understand [[environmental issues|environmental impacts]] in the hopes of mitigating these impacts.<ref>{{cite journal |last1=Thompson |first1=Kirsten F. |last2=Miller |first2=Kathryn A. |last3=Currie |first3=Duncan |last4=Johnston |first4=Paul |last5=Santillo |first5=David |title=Seabed Mining and Approaches to Governance of the Deep Seabed |journal=Frontiers in Marine Science |date=2018 |volume=5 |doi=10.3389/fmars.2018.00480 |s2cid=54465407 |doi-access=free |hdl=10871/130176 |hdl-access=free }}</ref>

=== Technetium ===

{{Main article|Technetium#Occurrence and Production}}
Technetium was created by bombarding [[molybdenum]] atoms with [[deuteron]]s that had been accelerated by a device called a [[cyclotron]]. Technetium occurs naturally in the Earth's [[Crust (geology)|crust]] in minute concentrations of about 0.003 parts per trillion. Technetium is so rare because the [[half-life|half-lives]] of <sup>97</sup>Tc and <sup>98</sup>Tc are only 4.2&nbsp;million&nbsp;years. More than a thousand of such periods have passed since the formation of the [[Earth]], so the probability of survival of even one atom of [[primordial nuclide|primordial]] technetium is effectively zero. However, small amounts exist as spontaneous [[fission product]]s in [[uranium ore]]s. A kilogram of uranium contains an estimated 1&nbsp;[[Orders of magnitude (mass)|nanogram]] (10<sup>−9</sup>&nbsp;g) equivalent to ten trillion atoms of technetium.<ref name="blocks">{{harvnb|Emsley|2001|pp=[https://archive.org/details/naturesbuildingb0000emsl/page/422 422]–425}}</ref><ref>{{cite journal|doi=10.1021/ac961159q |title=Analysis of Naturally Produced Technetium and Plutonium in Geologic Materials|date=1997 |last1=Dixon|first1=P.|last2=Curtis|first2=David B. |last3=Musgrave|first3=John |last4=Roensch|first4=Fred|last5=Roach|first5=Jeff|last6=Rokop|first6=Don|journal=Analytical Chemistry |volume=69|issue=9|pages=1692–1699|pmid=21639292}}</ref><ref>{{cite journal |doi=10.1016/S0016-7037(98)00282-8 |title=Nature's uncommon elements: plutonium and technetium|last1=Curtis|first1=D. |last2=Fabryka-Martin|first2=June|last3=Dixon|first3=Paul|last4=Cramer|first4=Jan|date=1999 |journal=Geochimica et Cosmochimica Acta |volume=63|issue=2|pages=275|bibcode=1999GeCoA..63..275C |url=https://digital.library.unt.edu/ark:/67531/metadc704244/}}</ref> Some [[red giant]] stars with the spectral types S-, M-, and N contain a spectral absorption line indicating the presence of technetium.{{sfn|Hammond|2004|loc=[https://archive.org/details/crchandbookofche81lide/page/n905 p. 4-1]}}<ref>{{cite journal|doi=10.1126/science.114.2951.59|date=1951 |last1=Moore|first1=C. E.|title=Technetium in the Sun|journal=Science |volume=114 |issue=2951 |pages=59–61 |pmid=17782983|bibcode=1951Sci...114...59M}}</ref><!--Technetium in Red Giant Stars P Merrill&nbsp;— Science, 1952--> These red giants are known informally as [[technetium star]]s.

=== Rhenium ===
{{Main article|Rhenium#Production}}

[[Image:Molybdenit 1.jpg|thumb|left|Molybdenite]]
Rhenium is one of the rarest elements in [[Earth's crust]] with an average concentration of 1&nbsp;ppb;<ref name="G&W" /><ref name=":1">{{Cite web|url=https://www.rsc.org/periodic-table/element/75/rhenium|title=Rhenium - Element information, properties and uses {{!}} Periodic Table|website=www.rsc.org|access-date=2019-12-02}}</ref> other sources quote the number of 0.5&nbsp;ppb making it the 77th most abundant element in Earth's crust.{{sfn|Emsley|2001|pp=[https://archive.org/details/naturesbuildingb0000emsl/page/358 358–360]}} Rhenium is probably not found free in nature (its possible natural occurrence is uncertain), but occurs in amounts up to 0.2%<ref name="G&W" /> in the mineral [[molybdenite]] (which is primarily [[molybdenum disulfide]]), the major commercial source, although single molybdenite samples with up to 1.88% have been found.<ref name="Rousch" /> [[Chile]] has the world's largest rhenium reserves, part of the copper ore deposits, and was the leading producer as of 2005.<ref>{{cite web|url=http://minerals.usgs.gov/minerals/pubs/country/2005/cimyb05.pdf |first=Steve T.|last=Anderson| publisher=[[United States Geological Survey]]|title=2005 Minerals Yearbook: Chile|access-date=2008-10-26}}</ref> It was only recently that the first rhenium [[mineral]] was found and described (in 1994), a rhenium [[sulfide mineral]] (ReS<sub>2</sub>) condensing from a [[fumarole]] on [[Kudriavy]] volcano, [[Iturup]] island, in the [[Kuril Islands]].<ref>{{cite journal|last=Korzhinsky|first=M. A.|author2=Tkachenko, S. I. |author3=Shmulovich, K. I. |author4=Taran Y. A. |author5= Steinberg, G. S. | date=2004-05-05|title=Discovery of a pure rhenium mineral at Kudriavy volcano|journal=[[Nature (journal)|Nature]]|volume=369|pages=51–52|doi=10.1038/369051a0|issue=6475|bibcode = 1994Natur.369...51K |s2cid=4344624}}</ref> Kudriavy discharges up to 20–60&nbsp;kg rhenium per year mostly in the form of rhenium disulfide.<ref>{{cite journal| last1 = Kremenetsky| first1 = A. A.| last2 = Chaplygin| first2 = I. V.| title = Concentration of rhenium and other rare metals in gases of the Kudryavy Volcano (Iturup Island, Kurile Islands)| journal = Doklady Earth Sciences| volume = 430| issue = 1| page = 114| date = 2010| doi = 10.1134/S1028334X10010253|bibcode = 2010DokES.430..114K | s2cid = 140632604}}</ref><ref>{{cite journal | last1 = Tessalina | first1 = S. | last2 = Yudovskaya | first2 = M. | last3 = Chaplygin | first3 = I. | last4 = Birck | first4 = J. | last5 = Capmas | first5 = F. | title = Sources of unique rhenium enrichment in fumaroles and sulphides at Kudryavy volcano | journal = Geochimica et Cosmochimica Acta | volume = 72 | page = 889 | date = 2008 | doi = 10.1016/j.gca.2007.11.015 | bibcode=2008GeCoA..72..889T | issue = 3}}</ref> Named [[rheniite]], this rare mineral commands high prices among collectors.<ref>{{cite web|url=http://www.galleries.com/minerals/sulfides/rheniite/rheniite.htm|publisher=Amethyst Galleries|title=The Mineral Rheniite}}</ref> <!--Dr. Kremenetsky from [[Russian Academy of Sciences|RAS]] Mineralogy Institute argues that this source could be commercially exploited,<ref>[http://www.nkj.ru/archive/articles/5340/ Завод на вулкане] // Наука и жизнь, № 11, 2000, in Russian.</ref> but currently there is no active attempts to extract it.-->

[[Image:Ammonium perrhenate.jpg|thumb|right|Ammonium perrhenate]]

Most of the rhenium extracted comes from [[Porphyry (geology)|porphyry]] [[molybdenum]] deposits.<ref>{{cite book|chapter=Chapter 7: By-Products of Porphyry Copper and Molybdenum Deposits|first1=D. A.|last1=John|first2=R. D.|last2=Taylor|title=Rare earth and critical elements in ore deposits|year=2016|volume=18|pages=137–164|doi=10.5382/Rev.18.07 |url=https://pubs.er.usgs.gov/publication/70048652|editor=Philip L. Verplanck and Murray W. Hitzman}}</ref> These ores typically contain 0.001% to 0.2% rhenium.<ref name="G&W"/> Roasting the ore volatilizes rhenium oxides.<ref name="Rousch">{{cite journal|doi = 10.1021/cr60291a002|title = Recent advances in the chemistry of rhenium|date = 1974|author = Rouschias, George|journal = Chemical Reviews|volume = 74|page = 531|issue = 5}}</ref> [[Rhenium(VII) oxide]] and [[perrhenic acid]] readily dissolve in water; they are leached from flue dusts and gasses and extracted by precipitating with [[potassium chloride|potassium]] or [[ammonium chloride]] as the [[perrhenate]] salts, and purified by [[Recrystallization (chemistry)|recrystallization]].<ref name="G&W" /> Total world production is between 40 and 50 tons/year; the main producers are in Chile, the United States, Peru, and Poland.<ref name="USGS_2012_summary">{{cite web|title=Rhenium|work=Mineral Commodity Summaries |publisher=U.S. Geological Survey|date=January 2012|url=http://minerals.usgs.gov/minerals/pubs/commodity/rhenium/mcs-2012-rheni.pdf|first=Michael J.|last=Magyar|access-date=2013-09-04}}</ref> Recycling of used Pt-Re catalyst and special alloys allow the recovery of another 10 tons per year. Prices for the metal rose rapidly in early 2008, from $1000–$2000 per [[kilogram|kg]] in 2003–2006 to over $10,000 in February 2008.<ref name="minormetals">{{cite web|title=MinorMetal prices|publisher=minormetals.com|url=http://www.minormetals.com/|access-date=2008-02-17|archive-date=2008-05-15|archive-url=https://web.archive.org/web/20080515180506/http://www.minormetals.com/|url-status=dead}}</ref><ref>{{cite web|url=http://in.reuters.com/article/oilRpt/idINL1037587920080710|first=Jan|last=Harvey|title=Analysis: Super hot metal rhenium may reach "platinum prices"|date=2008-07-10|access-date=2008-10-26|publisher=Reuters India|archive-date=2009-01-11|archive-url=https://web.archive.org/web/20090111183605/http://in.reuters.com/article/oilRpt/idINL1037587920080710|url-status=dead}}</ref> The metal form is prepared by reducing [[ammonium perrhenate]] with [[hydrogen]] at high temperatures:<ref name="Brauer" />

:2 NH<sub>4</sub>ReO<sub>4</sub> + 7 H<sub>2</sub> → 2 Re + 8 H<sub>2</sub>O + 2 NH<sub>3</sub>
:There are technologies for the associated extraction of rhenium from productive solutions of underground leaching of uranium ores.<ref>{{Cite journal |last1=Rudenko |first1=A.A. |last2=Troshkina |first2=I.D. |last3=Danileyko |first3=V.V. |last4=Barabanov |first4=O.S. |last5=Vatsura |first5=F.Y. |title=Prospects for selective-and-advanced recovery of rhenium from pregnant solutions of in-situ leaching of uranium ores at Dobrovolnoye deposit |url=https://mst.misis.ru/jour/article/view/287 |journal=Gornye Nauki I Tekhnologii = Mining Science and Technology (Russia) |year=2021 |volume=6 |issue=3 |pages=158–169|doi=10.17073/2500-0632-2021-3-158-169 |s2cid=241476783 |url-access=subscription }}</ref>

=== Bohrium ===

Bohrium is a synthetic element that does not occur in nature. Very few atoms have been synthesized, and also due to its radioactivity, only limited research has been conducted. Bohrium is only produced in nuclear reactors and has never been isolated in pure form.