cassiterite: the tin dioxide, crystalline, heavy, gray, often twinned. It is mined mainly from alluvial deposits. Large deposits of cassiterite are found in Bolivia . But in recent years, with the increased demand for tin for the construction of electronic devices, has begun to remove it and sell it illegally in Democratic Republic of Congo .
Coltan : is a mineral immense economic and strategic importance. In particular, experts explain, is used to optimize the use of electricity in the new chip generation. Coltan is radioactive and contains a lot 'of uranium. The columbite-tantalite or columbo-tantalite , full name of the coltan, is a complex mixture of columbite ( Fe, Mn ) Nb 2 O 6 and tantalite ( Fe, Mn ) Ta 2 O 6 , two class mineral oxides that are very rarely as pure terms. The commercial value of tantalum is very high, so even a low production, such as the DRC, can provide high economic benefits. Since global demand for tantalum has become significant, has become particularly keen struggle between paramilitary groups and guerrillas for control of the Congolese territory where we extract the columbo-tantalite. One area particularly affected is that of the Kivu Republic Congo and two neighboring states: Rwanda and Uganda . Brokers who deal with illegal sales to Rwanda and Uganda SUPPLY, in fact, the Congolese mineral deposits. The money raised by the sale of the ore (as well as other valuable natural resources) by the guerrillas who control the eastern provinces of Congo, fund the civil war in these areas. The fact that armed groups or non state-owned companies and industry representatives, to attach themselves to the ore and sell to buyers with large revenue mainly Western or Asian does not in itself constitute a crime, none of the states involved has complicated the problem. Purchase of columbo-tantalite Congolese would be affected as intermediaries also European and Asian criminal organizations involved in the smuggling of illegal weapons that would exchange weapons for ore to sell. The issue of uncontrolled exploitation of Congolese resources is severe enough to have also involved the public in October 2002 a UN report that accused companies engaged in the exploitation of natural resources of the African country, among them the coltan , went on to indirectly favor the Civil War. For the purchase of columbite-tantalite was also involved the HC Starck, a subsidiary of Bayer that deals with the refinement of transition metals such as molybdenum, niobium, tantalum, tungsten and rhenium and production for the market of electronics, semiconductors and superconductors precision parts in special alloys and ceramic components. The 2002 report was also the basis of a conviction of a general by the UN Security Council in 2003 on the exploitation of natural resources in the Democratic Republic of Congo in which more than the columbite-tantalite, diamonds, emeralds , uranium, gold and other precious metals. The Tantalum-Niobium International Study Centre urged its members to take care to avoid procurement of columbo-tantalite Congolese and Rwandan denounced as ethically unacceptable in this business since the sale of the mineral in the countries finances and financed the civil war that has created over environmental damage for the indiscriminate exploitation.
Tantalum : Its symbol is Ta . It is a transition metal hard and malleable, shiny, blue-gray, very resistant to corrosion, especially the attack of acids , and is a good conductor of heat and electricity. It is rather rare in nature and is found in mineral tantalite . Tantalum is used in surgical instruments and implants in the intracorporeal, why does not react with body fluids. is highly resistant to corrosion, in practice, at temperatures below 150 ° C, it can be considered completely immune to chemical attack, even at extremely Aggressive substances such as' aqua regia , and can be affected only from ' hydrofluoric acid, from acid solutions containing fluoride ion and free sulfur trioxide. Tantalum has a high melting point, surpassed only from tungsten and rhenium (3290 K melting point, boiling point 5731 K). The major use for tantalum, in the form of metallic powder is in the production of electronic components, mainly tantalum, very small in relation to their capacity. These are used in almost all portable electronic devices such as cell phones, pagers , laptops and electronics for the car. Tantalum is also used in a wide variety of alloys with high melting point, high strength and good ductility. Alloyed with other metals is also used for the manufacture of carbide tools for metal working and production of superalloys for jet engines, instrumentation, laboratory chemical and nuclear reactors and missile parts. Other uses: Its ductility makes it possible to make very fine wire, used as electrical heaters to evaporate other metals such as aluminum. Because of its chemical inertness, tantalum is also used for surgical instruments. The tantalum oxide glass is used for high refractive index used in the lenses of the cameras. Tantalum is also used to make vacuum furnace parts . Tantalum is used in the preparation of chemical plants due to its high corrosion resistance. Tantalum is found mainly in the mineral tantalite [( Fe, Mn ) Ta 2 O 6] and euxenite (other minerals: samarskite and fergusonite ). The tantalite is often mixed with columbite in a mineral called columbite-tantalite (colloquially coltan). By the extraction of coltan have arisen numerous ethical issues, human rights and environmental protection, due to exploitation indiscriminate deposits of coltan in the Congo region torn by civil war.
commercially exploited tantalum ore deposits exist in Australia, Brazil, Canada, Zaire, Mozambique , Nigeria, Portugal and Thailand. The separation of tantalum from niobium requires a long process, composed of many complicated steps. Commercial production of this element can take advantage of a variety of methods, including the ' electrolysis fluorotantalato of potassium.
Cobalt : It is a silvery-white element, ferromagnetic and very hard. His Curie temperature is 1388 K with 1.6 ~ 1.7 magnetons per atom. It is often associated with nickel , and both are characteristic components of meteoric iron . Mammals require small amounts of cobalt salts in the diet. The 60 Co, one of his artificial radioactive isotope, is an important radioactive tracer and is used to treat many cancers. Cobalt has a relative permeability of two-thirds that of iron. Cobalt metal is usually a mixture two different crystal structures, hcp and fcc , with a transition temperature from hcp to fcc of 722 K.fuso or a reduced sodium, or the reaction between tantalum carbide and tantalum oxide. The tantalum is extracted as a by-product of the pond . It is rare to find compounds of tantalum, the metal and usually does not create hazards or safety issues in laboratories. However, the compounds of tantalum must be considered highly toxic, as clear evidence that they are carcinogenic. The powder of this metal can ignite or even explode if heated. Cobalt and its salts are used in many industries and applications: metal alloys, such as those used in the production of turbines for aircraft engines, high-strength alloys to corrosion and wear, high-speed tool steel, diamond tools, magnets and magnetic recording media, catalysts for petrochemical and chemical industries, a coating material for electrodeposition (electroplating ), for its appearance, its resistance and its hardness, dehydrating compounds in paints, lacquers and inks, powders for the coating of porcelain and enamels, pigments ( cobalt blue and cobalt green ) electrodes for car batteries. Cobalt-60, radioactive, is used as a source of gamma rays : is used in radiotherapy for the sterilization of food by radiation (cold pasteurization), in industrial radiography to detect structural abnormalities in fabricated metal products. Its use as a radioactive tracer is very popular because it is easy to produce, it is obtained by exposing natural cobalt to neutrons products from a nuclear reactor. Cobalt-60 (Co-60 or 60 Co) is a radioactive metal used in radiotherapy , producing gamma rays with energy of 1.17 MeV and 1.33 MeV. A normal source 60 Co ha un diametro di circa 2cm e produce un cono di radiazione circondato da una zona di penombra . Il cobalto metallico ha la pessima proprietà di produrre una finissima polvere, causando problemi di protezione dalle radiazioni. Le sorgenti 60 Co hanno una vita utile di circa cinque anni, dopodiché non emettono più raggi gamma in quantità sufficiente: tuttavia restano comunque molto radioattive, ragione per cui in occidente l'uso delle macchine al cobalto è sempre più raro, preferendo usare acceleratori lineari di particelle. La prima macchina al 60 Co per terapia medica (la famosa bomba al cobalto ) fu costruita in Canada; is now on display at Saskatoon Cancer Centre, up the hall. The second machine is out of the center, along the promenade. Cobalt is found in many living organisms, including humans. A cobalt content 0.13 to 0.30 parts per million soil significantly improves the health of farm animals. Cobalt is a key element in vitamin B-12 . Cobalt is not pure metal, but only as a mineral, and is not mined alone, but as a byproduct of copper mining or nickel. The most important minerals of cobalt are cobaltite , the ' erythrite the glaucodot and skutterudite . The major world producers of cobalt are the Congo, China, the Zambia, Russia and Australia. Cobalt metal dust can ignite spontaneously in air. Cobalt compounds should be handled with caution, because of their slight toxicity. The 60 Co, radioactive, is a powerful gamma ray emitter, so exposure to it increases the risk of cancer. Ingested, is only slowly eliminated from tissues. The 60 Co can be produced in case of nuclear war from the stable isotopes of iron and cobalt the effect of neutrons emitted by the devices. There are nuclear weapons specifically designed to increase the amount of 60 Co dispersed across the fallout .
0 comments:
Post a Comment