Mais conteúdo relacionado

Mining of Rare minerals from sea

  1. PRESENTATION ON PRESENted by: Swati FRM Deptt.
  2. Oceans cover 70 percent of Earth's surface. They hold a veritable treasure trove of valuable resources. They are the ultimate repository of many materials eroded or dissolved from the land surface. Sand and gravel, oil and gas have been extracted from the sea for many years. In addition, minerals transported by erosion from the continents to the coastal areas are mined from the shallow shelf and beach areas. These include diamonds off the coasts of South Africa and Namibia as well as deposits of tin, titanium and gold along the shores of Africa, Asia and South America.
  3.  Ancient ocean deposits of sediments and evaporites now located on land were originally deposited under marine conditions.  These deposits are being exploited on a very large scale and in preference to modern marine resources because of the easier accessibility and lower cost of terrestrial resources.  Yet the increasing population and the exhaustion of readily accessible terrestrial deposits undoubtedly will lead to broader exploitation of ancient deposits and increasing extraction directly from ocean water and ocean basins.
  4.  Efforts to expand ocean mining into deep-sea waters have recently begun.  The major focus is on manganese nodules, which are usually located at depths below 4000 metres, gas hydrates (located between 350 and 5000 metres), and cobalt crusts along the flanks of undersea mountain ranges (between 1000 and 3000 metres), as well as massive sulphides and the sulphide muds that form in areas of volcanic activity near the plate boundaries, at depths of 500 to 4000 metres.
  5. Manganese nodules  Manganese nodules are lumps of minerals ranging in size from a potato to a head of lettuce.  They cover huge areas of the deep sea with masses of up to 75 kilograms per square metre.  They are composed mainly of manganese, iron, silicates and hydroxides.  They grow around a crystalline nucleus at a rate of only about 1 to 3 millimetres per million years.  The greatest densities of nodules occur off the west coast of Mexico (in the Clarion-Clipperton Zone), in the Peru Basin, and the Indian Ocean. In the Clarion-Clipperton Zone the manganese nodules lie on the deep-sea sediments covering an area of at least 9 million square kilometres – an area the size of Europe.
  6. Cross-section view of a manganese nodule: Over millions of years, minerals are deposited around a nucleus.
  7. Cobalt crusts  Cobalt crusts form at depths of 1000 to 3000 metres on the flanks of submarine volcanoes.  The crusts accumulate when manganese, iron and a wide array of trace metals dissolved in the water (cobalt, copper, nickel, and platinum) are deposited on the volcanic substrates.  The content of cobalt (up to 2 per cent) and platinum (up to 0.0001 per cent) is somewhat higher than in manganese nodules.  Extracting cobalt from the ocean is of particular interest because it is found on land in only a few countries (Congo, Zaire, Russia, Australia and China).
  8.  The mining of cobalt crusts is much more complex than manganese nodules.  For one, it is critical that only the crust is removed, and not the underlying volcanic rocks.  In addition, the slopes of the volcanoes are very ragged and steep, which makes the use of excavation equipment more difficult.
  9. Massive sulphides  These are sulphur-rich ore that originates at “black smokers”.  These were first discovered in 1978 at the East Pacific Rise.  They are also located in comparatively shallow water (less than 2000 metres) and lie within the exclusive economic zones of nations near them which makes the possible mining more technologically and politically feasible.  Most occurrences are only a few metres in diameter and the amount of material present is negligible. Massive sulphides form at black smokers – hot springs on the sea floor with temperatures approaching 400 degrees Celsius. These vents discharge minerals from the Earth’s interior, forming chimneys that rise to several metres above the seabed.
  10. Production of massive sulphides  These occurrences of massive sulphides form at submarine plate boundaries, where an exchange of heat and elements occurs between rocks in the Earth’s crust and the ocean due to the interaction of volcanic activity with seawater.  Cold seawater penetrates through cracks in the sea floor down to depths of several kilometres.  Near heat sources such as magma chambers, the seawater is heated to temperatures exceeding 4000C.  Upon warming, the water rises rapidly again and is extruded back into the sea. These hydrothermal solutions transport metals dissolved from the rocks and magma, which are then deposited on the sea floor and accumulate in layers.  This is how the massive sulphides and the characteristic chimneys (“black smokers”) are produced.
  11. Other marine minerals found in seabed  Gabbro  Peridotite  Basalt  Olivine  Serpentine
  12. Gabbro Dark in color -black or gray -and is a coarse-grained igneous rock that makes up most of the seabed. Dense type of rock formed from the slow cooling of magma chambers beneath mid-ocean ridges. Used in railroads, road material and can be polished to be sold as black granite. Basalt Very similar to gabbro in its chemical composition. Most often black in color. Basalt is the most extrusive igneous rock. Used as construction material, flooring and sculpting. Peridotite Textured with black, gray and white coloring. Dense, intrusive igneous rock that is rich in magnesium and iron. Contains olivine in its composition, another mineral found under seabeds. Found as layers, crystals and fragmented blocks. Named after the gemstone peridot. Used to capture and store carbon dioxide.
  13. Serpentine Green in color, but can also be yellow, black or brown. It is an alteration form of the mineral olivine. Used as a substitute for jade and can be used for carving. Olivine  Brownish-green to dark or olive green in color.  Commonly found in basalt, gabbro and peridotite.  It is a silicate mineral, which are common rock formers.  It is used in jewellery, as peridot, when mixed with peridotite.
  14. Deep sea mining  Deep-sea mining is the process of retrieving mineral deposits from the deep sea – the area of the ocean below 200 m which covers about 65% of the Earth’s surface.  Depleting terrestrial deposits and rising demand for metals are stimulating interest in the deep sea, with commercial mining imminent.  China is the world’s largest consumer and importer of minerals and metals.
  15. Ocean mining in India  India’s ambitious ‘Deep Ocean Mission’ is all set to be launched this year.  Dr. Madhavan Rajeevan, Secretary, Union Ministry of Earth Sciences, announced on July 27 that the ₹8,000-crore plan to explore deep ocean minerals will start from October.
  16. What will be mined from the deep ocean?  One of the main aims of the mission is to explore and extract polymetallic nodules.  These are small potato-like rounded accretions composed of minerals such as manganese, nickel, cobalt, copper and iron hydroxide.  They lie scattered on the Indian Ocean floor at depths of about 6,000 m and the size can vary from a few millimetres to centimetres.  These metals can be extracted and used in electronic devices, smartphones, batteries and even for solar panels.
  17. Where will the team mine?  The International Seabed Authority (ISA), an autonomous international organisation established under the 1982 United Nations Convention on the Law of the Sea, allots the ‘area’ for deep- sea mining.  India was the first country to receive the status of a ‘Pioneer Investor ‘ in 1987 and was given an area of about 1.5 lakh sq km in the Central Indian Ocean Basin (CIOB) for nodule exploration.  In 2002, India signed a contract with the ISA and after complete resource analysis of the seabed 50% was surrendered and the country retained an area of 75,000 sq km.
  18. According to a release from the Ministry of Earth Sciences, the estimated polymetallic nodule resource potential in this area is 380 million tonnes (MT), containing 4.7 MT of nickel, 4.29 MT of copper, 0.55 MT of cobalt and 92.59 MT of manganese.
  19. Impacts of mining The following impacts of mining activities could affect its biodiversity and ecosystems: (i)Disturbance of the seafloor  The scraping of the ocean floor by machines can alter or destroy deep- sea habitats, leading to the loss of species and fragmentation or loss of ecosystem structure and function.  Many species living in the deep sea are endemic and physical disturbances in just one mining site can possibly wipe out an entire species.  This is one of the biggest potential impacts from deep-sea mining.
  20. (ii)Sediment plumes Some forms of deep-sea mining will stir up fine sediments on the seafloor consisting of silt, clay and the remains of microorganisms, creating plumes of suspended particles. (iii)Pollution Species such as whales, tuna and sharks could be affected by noise, vibrations and light pollution caused by mining equipment and surface vessels, as well as potential leaks and spills of fuel and toxic products.
  21. Mitigation strategies Baseline studies  Comprehensive baseline studies are needed to understand what species live in the deep sea, how they live, and how they could be affected by mining activities.  More funds are needed for training and educational programmes focused on improving our understanding of the deep sea. Circular economy  The repair, recycling and reuse of products should be encouraged to help reduce the demand for raw materials from the deep sea.  Enhancing product design to make use of less or alternative materials can also reduce the demand.
  22. Environmental impact assessments  High-quality environmental assessments are needed to assess the full range, extent and duration of environmental damage from deep- sea mining operations.  These assessments are also needed to ensure that the loss of biodiversity as a result of mining operations is properly accounted for in mining regulations set by authorities, well before any decision to mine is approved.
  23. REFERENCES:  › Sci-Tech › Science  › wor-1 › energy › marine-minerals  › Mi-Oc  › library › sites › library › files › documents