Editing Group 7 element (section)

=== 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>