olelog

Manganese nodules were first discovered on the ocean floor in 1803. Manganese nodules, are rock concretions on the sea bottom formed of concentric layers of iron and manganese hydroxides around a core or nucleus. Nodules lie on the seabed sediment, often partly or completely buried. They vary greatly in abundance, in some cases touching one another and covering more than 70 per cent of the bottom. They may contain up to 70% manganese, around 15% iron, and further some copper, cobalt, zinc and nickel in small proportions.

Nodule growth is extremely slow – on the order of a centimeter over several million years. Several processes are involved in the formation of nodules, including the precipitation of metals from seawater (hydrogenous), the remobilization of manganese in the water column (diagenetic), the derivation of metals from hot springs associated with volcanic activity (hydrothermal), the decomposition of basaltic debris by seawater (halmyrolitic) and the precipitation of metal hydroxides through the activity of microorganisms (biogenic). Several of these processes may operate concurrently or they may follow one another during the formation of a nodule.

Since the 1960's manganese nodules have been recognized as a potential ore source. Germany seems finally willing to do something serious about it.

Bundesanstalt für Geowissenschaften und Rohstoffe (BGR) in Hannover, Germany, has from the International Seabed Authority received an exploration licence for 15 years in 75.000 km2 sea-bed of the Pacific Ocean between Mexico and Hawaii - in the Pacific Nodule Belt between the Clarion and Clipperton fracture zones.

German geologists recently carried out an extended research project in the Pacific. They wanted to find out how many manganese nodules there are, and where they are scattered. 24 million tons of precious metals are believed to be lying under the world’s oceans. The German geologists are trying to learn whether the nodules could be recovered from the seabed without damaging the environment, and which technology would be best suited to do that.

The Pacific nodules contain on average 15-30% manganese, 7-15% iron, 1,2% nickel, 1% copper and 0,3% cobalt. They can have a diameter of up to 50 cm and are mainly found at a depth of 4-5 km. Together they may contain thousands of billions of tons manganese.

The area between the Clarion and Clipperton fracture zones and the areas belonging to different contractors are shown on this map. (If you have difficulties with reading the small letters, I can tell you that the legend for the German area is the lowest one in the legend box.)

• http://www.deutsche-welle.de/dw/article/0,,4408892,00.html
  
• http://www.cartage.org.lb/en/themes/sciences/Earthscience/Oceanography/OceanSediments/Manganesenodules/Manganesenodules.htm
  
• http://www.springerlink.com/content/44p012947k652226/
  

In Danish:

• http://ing.dk/artikel/101514-tyskland-vil-hente-metal-i-dybhavet?utm_medium=rss&utm_campaign=nyheder
  

In German:

• http://www.bgr.bund.de/nn_324952/DE/Gemeinsames/Oeffentlichkeitsarbeit/Pressemitteilungen/BGR/bgr__081002.html
  

Guinea is in the news just now because of the military coup after the death of the country's dictator for the last 24 years, Lansana Conté. I am interested because I am a West Africa fan. West Africa has a Gold Coast (Ghana) and an ivory Coast (Côte d'Ivoire). Guinea would deserve the name of the Bauxite Coast. Guinea could possibly have been the richest country (or at least one of the richest countries) in Africa based on the export of bauxite and other commodities if it had known a better leadership.


Guinea has the world's largest bauxite reserves (a third of the world's bauxite reserves) and is one of the biggest exporter of bauxite ore. Bauxite is the ore from which aluminium is produced. It is refined to produce alumina (aluminium oxide, Al₂O₃), which is further processed (by electrolysis) to make aluminium (Al). As the electrolysis demands an extremely lot of energy aluminum melting plants are often located in countries where electricity is cheap (e.g. due to hydroelectric plants). I have for instance seen a melting plant near Reykjavik in Iceland (in operation since 1969).

Aluminium is the most abundant metal in the Earth's crust, and the third most abundant element therein, after oxygen and silicon. It makes up about 8.3% by weight of the Earth’s solid surface. It is however extremely rarely found in native metal form. it was in fact once considered a precious metal more valuable than gold, because it was so hard to get at. You can become extremely rich if you can find an economic way to extract aluminium from normal clay (if such a thing as normal clay exist). Aluminium is (together with silica) abundant in all igneous rocks (like granite or basalt), mainly found in their feldspar minerals - feldspars are aluminum silicates or aluminosilicates. Aluminosilicates are also a major component of clay minerals.

Bauxite is named after Les Baux in southern France where it was discovered in 1821 by the geologist Pierre Berthier. Today Les Baux is very touristic. It is set atop a rocky limestone outcrop crowned with a ruined castle overlooking the plains to the south. Its name refers to its site - in Provençal a baou is a rocky spur.

Bauxite is a weathering product. After chemical weathering (e.g. of igneous rocks) aluminium can be concentrated in the silicate mineral, kaolinite (Al₂Si₂O₅(OH)₄). Rocks that are rich in kaolinite are known as china clay or kaolin. In tropical climate the greater availability of water (particularly in the rainy season) enables chemical weathering to progress further, so that silica is leached from kaolinite and aluminium hydroxide is left in the residue. The final weathering product may be a mixture of aluminium oxides and hydroxides of average composition Al₂O₃•2H₂O - namely bauxite. What metals will be transported away in solution, and what metals will be left in the residue is of course a question of their solubility in ground water. Two properties of aqueous environments are here of overriding importance, namely acidity (pH) and oxidation potential (Eh).

For those who are interested I have drawn an approximate Eh-pH diagram, showing the conditions required for transport of iron and silicon and deposition of aluminium - and thereby for formation of bauxite. Oxidising solutions have values of Eh greater than 0.4 volts - a condition met in waters very close to the surface. Lower values mean a reducing potential. The main conclusion is that bauxite is formed under reducing conditions.

We may distinguish between lateritic bauxites (silicate bauxites) - as described above - and karst bauxites (carbonate bauxites). The early discovered carbonate bauxites occur predominantly in Europe and Jamaica above carbonate rocks (limestone and dolomite), where they were formed by weathering and residual accumulation of clays in limestone. I have seen such deposits in Greece, where they are still mined.

Jamaica is still a principal source of bauxite. The presence of aluminium in the red soil of Jamaica was recognised as early as 1869. Consequently there is a lot of literature about the Jamaican bauxite. In 2007, Australia was the top producer of bauxite with almost one-third world share, followed by China, Brazil, Guinea, and Jamaica.

In Europe, aluminium enjoys high recycling rates, ranging from 41% in beverage cans to 85% in building and construction and 95 % in transportation. Since the material can be recycled indefinitely without loss of quality, and because of the high intrinsic value, there are strong natural incentives to recover and recycle aluminium products after use. Comprehensive systems for the recovery of used aluminium now exist in all major European countries. 32% percent of European aluminium demand is satisfied by recycled material. A large majority of recycled aluminium is consumed by the transport sector. The other main markets are engineering, packaging and building.

• http://www.nationsencyclopedia.com/Africa/Guinea-MINING.html
• http://www.mining-technology.com/projects/cbg/



PS: See also "Guinean junta warns mining sector" from BBC at http://news.bbc.co.uk/2/hi/africa/7800819.stm