Manganese nodule

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Manganese nodule, image width: 20 cm
Close-up of a manganese nodule, image width: 3 cm

Manganese nodules are lumps that consist of up to 27% of the metal manganese . They can be found at depths between 4000 and 6000 meters on the sea ​​floor . Other elements such as copper , cobalt , zinc and nickel are 0.2–1%, the iron content is 15%.

Origin and structure

Manganese nodules grow extremely slowly (about 5 mm in a million years). About 15% of the manganese comes from the calcareous shells of dead microorganisms, which dissolved at the calcite compensation depth . This part is called the hydrogenetic part. Most of the manganese comes from the sediment . While the manganese in the sediment is dissolved in pore water in its divalent form, it is oxidized to its tetravalent form by the oxygen-rich Antarctic bottom currents when it reaches the sea floor and is thus present as water-insoluble MnO 2 . The biogenic divalent manganese coming from above is deposited in the same way.

The internal structure of the tubers is comparable to that of an onion. The tubers contain a shell-shaped core that can be made of various materials. The largest sites for manganese nodules are in the Pacific Ocean . In this ocean alone, an amount of around 100 million tons is expected.

Removal of manganese nodules

An alleged experimental program to mine manganese nodules in the early 1970s was camouflage for the Azorian project , the secret recovery of a Soviet submarine .

In the period from February to May 1978, an international consortium, OMI (Ocean Management Inc.), extracted several hundred tons of manganese nodules from a depth of 5000 m for the first time in a successful pilot mining test in the Central Pacific. It was shown that both the concept of hydraulic vertical conveying by means of pumps and the air-lift method (airlift method, mammoth pump ) are suitable for the extraction of manganese nodule fields, even though this attempt did not yet achieve an economical conveying capacity - not even in the short term. The consortium consisted of the following members:

  • AMR (Working Group on Mining Raw Materials, Federal Republic of Germany)
  • DOMCO (Deep Ocean Mining Corp., Japan)
  • INCO (International Nickel Comp. Ltd., Canada)
  • SEDCO (South East Drilling Corp. Inc., USA)

In the early 1980s, manganese nodules were extensively studied by mineralogists and chemists for clues about their growth and composition. Their metallurgical value, especially with regard to the nickel and copper content of the tubers, was also discussed. The two images show a manganese nodule from a collection that was examined mineralogically at the Institute for Mineralogy at the University of Heidelberg .

In order to ensure economical, unsubsidized mining of manganese nodules, around one and a half to two million dry tons of valuable mineral would have to be extracted every year, taking into account current production factors and market prices (2016). The production capacity is limited to around two million dry tons per mining system due to the geologically specified occupancy density and the area to be managed during this time. Such a mining concept was developed as part of the Blue Mining research project: It provides that the manganese nodules occurring on the surface are picked up by one or two remote-controlled collecting devices, freed of sediment and crushed for vertical transport. The machines are designed so that there is as little interference with nature as possible. The degradation process and the environmental impacts in the deep sea have not yet been researched in sufficient detail. It is expected that mining on the seabed will be similar to the process of potato harvest in agriculture. It is assumed that an average of four to five soccer fields per hour of production have to be cultivated in order to achieve an annual tonnage of two million dry tons. The mining concept also provides that mining in the deep sea is accompanied by a large number of different remote-controlled underwater vehicles, among other things for recording and assessing the navigability of the sea surface and the stock of manganese nodules. However, suitable technologies still have to be (further) developed. The ore collected in this way is transported via a flexible conveyor line to an intermediate storage facility, which is connected to the production ship via the vertical conveyor pipe. As part of the Blue Mining project, two different technologies are being researched: On the one hand, a pumping system that is widely used in the wet extraction of industrial minerals, but has been improved for a depth of up to 6,000 meters, and on the other hand, an air lifting process provided by MH Wirth. On the production ship, the ore is drained, temporarily stored and loaded onto bulk carriers for lateral transport at intervals of five to eight days. Sea water and small fractions of sediment and manganese nodule substrate from drainage are returned to sufficient water depths. So far there are no processing plants for manganese nodules on land. In Germany, research is being carried out on dismantling concepts at RWTH Aachen University . The metallurgical smelting of the manganese nodules and the refining of the intermediate products are currently being researched at the Clausthal University of Technology and the RWTH Aachen University. The concept envisages that manganese nodules are melted in a smelting reduction furnace in order to produce an alloy rich in valuable metals and a manganese-rich slag. Excess iron can be removed from the alloy by blowing in oxygen. The alloy can then be hydrometallurgically refined to produce nickel , cobalt and copper as carbonate , sulfate and metal. The slag from the first smelting process can be processed into ferromanganese in a further smelting reduction furnace . Residues from hydrometallurgical refining can also be used in this step. The slag produced in the second melting process only contains low concentrations of heavy metals and could be used in the building materials industry.

German resource research area in the Pacific

see also German Resource Research Area in the Pacific

Since 2006, Germany has held a research license through the Federal Institute for Geosciences and Natural Resources (BGR) in Hanover for two areas in the Pacific covering a total of 75,000 square kilometers. In 2006, Germany paid the UN 250,000 euros for a lease. The two sea areas are located southwest of Hawaii , in the so-called "manganese belt" which stretches from the coast of Mexico to Hawaii. The water depths in the area are between 4000 and 6000 m. The sea floor is densely covered with polymetallic nodules. The tubers are usually between 3 and 8 cm in size. In addition to an average of 25 percent manganese, they also contain around 3 percent copper , nickel and cobalt . These last three “valuable metals” in particular are of interest as a raw material source for future use. Other trace metals that occur in interesting concentrations in the tubers are molybdenum , lithium and neodymium , but also antimony , bismuth , germanium , indium , selenium , tellurium and the like. a.

The license allows exploring the manganese nodule deposits for 15 years. A mining license must be applied for from the International Seabed Authority for possible mining . The effects of the extraction of raw materials on the oceanic habitats are assessed by the Federal Environment Agency as "considerable" . With the international research initiative JPI Oceans, the Federal Ministry of Education and Research is promoting research into the ecological effects of potential deep-sea mining. On several research trips with the research ship Sonne, the scientists investigated whether degradation of the manganese nodules in the deep sea would endanger the species that live there. The scientists found out that the previous communities in the regions where manganese nodules were removed no longer exist in the same species composition. The subject of deep-sea resources, deep-sea mining and its ecological consequences was brought up by the Federal Ministry of Education and Research in 2015 in the G7 talks of science ministers. In addition, a delegation traveled to the international seabed authority ISA in summer 2016 to present the research results and thus help shape the mining code. The scientists gave the recommendation to create protected areas and mining areas with the same tuber density and species composition like a mosaic.

literature

  • G. Ottow: Open pit under water . In: Die Umschau 82 , No. 10 (May 1982), pp. 319-324
  • David S.Cronan: Handbook of marine mineral deposits ; Boca Raton, Florida: CRC Press, 2000; ISBN 0-8493-8429-X
  • Günter Dorstewitz: Sea mining on cobalt, copper, manganese and nickel - coverage of needs, operating costs, profitability ; Verlag Glückauf, Essen 1971; ISBN 3-7739-0093-7
  • Peter Halbach: The manganese nodule belt of the Pacific Ocean - geological environment, nodule formation, and mining aspects ; Enke, Stuttgart 1988; ISBN 3-432-96381-5
  • Ranadhir Mukhopadhyay, Anil K. Ghosh, Sridhar D. Iyer: The Indian Ocean nodule field - geology and resource potential ; Elsevier Science & Technology, Amsterdam 2007; ISBN 978-0-444-52959-6
  • Thomas Kuhn et al .: Deep sea extraction of manganese nodules . In: Schiff & Hafen , issue 5/2011, pp. 78–83; Seehafen-Verlag, Hamburg 2011, ISSN  0938-1643

Web links

Commons : Manganese nodule  - collection of images, videos and audio files

Individual evidence

  1. ↑ Manganese nodules. Retrieved July 20, 2010 . mineralienatlas.de
  2. ↑ Blue Mining Project website , accessed on May 26, 2017.
  3. ↑ Sebastian Ernst Volkmann, Felix Lehnen: Production key figures for planning the mining of manganese nodules . In: Marine Georesources & Geotechnology . April 21, 2017, pp. 1–16. doi : 10.1080 / 1064119X.2017.1319448 .
  4. ↑ Peter Kukla, Felix Lehnen, Bernd Lottermoser, Mirjam Rahn, Sebastian Volkmann: Can manganese nodules be harvested in the Pacific like potatoes? RWTH Aachen, 2016, accessed on May 23, 2017 .
  5. ↑ Sebastian Ernst Volkmann, Thomas Kuhn, Felix Lehnen: A comprehensive approach for a techno-economic assessment of nodule mining in the deep sea . In: Mineral Economics . February 21, 2018, ISSN  2191-2203 , p. 1-18 , doi : 10.1007 / s13563-018-0143-1 .
  6. ^ Sebastian Ernst Volkmann, Bernd Georg Lottermoser, Peter A. Kukla: Blue mining - planning the mining of seafloor manganese nodules . Aachen 2018, doi : 10.18154 / rwth-2018-230772 ( rwth-aachen.de [PDF; 15.1 MB ; accessed on December 19, 2018] dissertation).
  7. ↑ Marcus Sommerfeld, David Friedmann, Thomas Kuhn, Bernd Friedrich: “Zero-Waste”: A Sustainable Approach on Pyrometallurgical Processing of Manganese Nodule Slags . In: Minerals . 8, No. 12, November 23, 2018, ISSN  2075-163X , p. 544. doi : 10.3390 / min8120544 .
  8. ↑ Sebastian Keber, Lisa Brückner, Tobias Elwert, Thomas Kuhn: Concept for a Hydrometallurgical Processing of a Copper ‐ Cobalt ‐ Nickel Alloy Made from Manganese Nodules . In: Chemical Engineer Technology . 92, March 11, 2020, ISSN  1522-2640 , pp. 379-386. doi : 10.1002 / cite.201900125 .
  9. ↑ planet-wissen.de
  10. ↑ Deep-sea mining and other uses of the deep sea . Federal Environment Agency , June 7, 2013; Retrieved July 26, 2016.
  11. ↑ fona.de