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Lectura Py

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    Acta Metallurica Slovaca, 13, 2007,3 420 - 433 420   NEW FRONTIERS IN EXTRACTIVE METALLURGY    Habashi F.    Department of Mining, Metallurgical, and Materials Engineering, Laval University, Quebec City, Canada G1K 7P4, e-mail:   NOV É  HRANICE V EXTRAK  I NEJ METALURGI Í     Habashi F.    Department of Mining, Metallurgical, and Materials Engineering, Laval University, Quebec City, Canada G1K 7P4, e-mail:   Abstrakt   K  ý m pyrometalurgia je najvhodnej  š ia met ó da spracovania vysoko bohat ý ch oxidick  ý ch r  ú d, hydrometalurgia je vhodn á  na spracovanie chudobn ý ch oxidick  ý ch r  ú d a taktie ž  e vhodn á  pre sulfidick  é  koncentr  á ty. Elektrometalurgia v s ú č asnosti dominuje pri v ý robe hlin í  ka, elektrolytickej rafin á ci í   medi, a elektrolytickom z í  skavan í   zinku. T á to met ó da bola taktie ž   ú spe  š n á  pri elektrolytickom z í  skavan í   medi z roztoku z í  skan é ho l ú hovan í  m  –  kvapalinovou extrakciou. Av  š ak, ak sa priemysel medi pos ú va smerom od tavenia ku tlakov é mu l ú hovaniu, potom elektrolytick  é  z í  skavanie kovov bude dominantn é  v oblasti hydro - elektrometalurgie. V s ú č asnosti v  š etky fakty poukazuj ú  na tlakov é  l ú hovanie ako v ý znamn ú  cestu spracovania meden ý ch sulfidick  ý ch koncentr  á tov v dvadsiatom prvom storo č í  . T á to technol ó gia sa teraz vyu ží  va na spracovanie zinkov ý ch sulfidick  ý ch koncentr  á tov a odoln ý c koncentr  á tov zlata a zmier  n uje probl é m zne c istenia SO 2 .   Abstract   While pyrometallurgy is most suitable for treating high grade oxide ores, hydrometallurgy is suitable for low grade oxide ores and for sulfide concentrates. Electrometallurgy is presently dominated by the production of aluminum, the electrorefining o copper, and the electrowinning of zinc. It has been also successful in the electrowinning o copper from solution obtained by leaching-solvent extraction. However, if the copper industry shifts from smelting to pressure leaching then electrowinning will dominate the area of aqueous electrometallurgy. At present all data point out to pressure leaching as the eminent route for treating copper sulfide concentrates in the twenty first century. This technology now used for treating zinc sulfide and refractory gold concentrates, alleviates pollution problems by SO 2 .   Key words: extractive metallurgy   Introduction   Extractive metallurgy is the science and engineering of extracting metals from ores. Closely related to this technology is mineral beneficiation whereby ores are treated by mechanical, physical, and physico-chemical means to prepare concentrates either for metal  production or to be used for the chemical and other industries as industrial minerals Fig. 1. Extractive metallurgy can be divided into three large sectors Fig.2.      Acta Metallurica Slovaca, 13, 2007,3 420 - 433 421   ·    Hydrometallurgy . The use of aqueous solutions   ·    Electrometallurgy . The use of electric current to effect a chemical reaction   Fig.1 Mineral processing   Fg.2 Extractve metaurgy s ve nto pyro-, yro-, an eectrometaurgy   Pyrometallurgy   Pyrometallurgy is the oldest of these technologies. The ancient Egyptians melted native gold Fig. 3 and produced copper and iron from their oxide ores by thermal methods. Furnaces increased in size Fig. 4, 5. Today it is the only route to produce iron and it is certain that it will remain so for many decades to come because pyrometallurgy is most suitable for the treatment of high grade oxide ores. Even when high grade iron ores are exhausted, it is possible to beneficiate the low grade ores and produce pellets suitable for reduction in the blast furnace which is a very efficient large reactor, being at the same time a heat exchanger.   Fig.3 Melting of ores was practiced by the ancient Egyptians      Acta Metallurica Slovaca, 13, 2007,3 420 - 433 422   Copper    Copper is another ancient metal. Like gold it also occurs in the native state but to a minor extent. Its main occurrences are as oxides or sulfides. In ancient civilizations, the oxides were extensively exploited by reduction with carbonaceous material (timber) in small furnaces. When man started to exploit the sulfides, new problems arose:   ·   Emission of large amounts of SO 2  because of the partial oxidation of the sulfides.   ·   The material melted during heating because of the formation of matte.   Fig.4 A Roman furnace to produce iron. To the left, a kiln for producing charcoal from timber    Fg.5 A nneteent century urnace   Eventually, a process was developed, known as the roast-reaction process, whereby the solidified matte was crushed and finely ground; half of it was oxidized then mixed thoroughly with the other half and the mixture was melted in a furnace with fluxes so that the roast-reaction between copper oxide and copper sulfide would take place to produce metallic copper, and at the same time iron was eliminated as a slag:      Acta Metallurica Slovaca, 13, 2007,3 420 - 433 423   2 CuO + Cu 2 S →  4 Cu + SO 2   The Welsh metallurgists were skilled in conducting this process, which became known as the Welsh Process. Matte from as far away as Butte, Montana and Chuquicamata, Chile was shipped to Swansea, Wales for transformation to copper. Sulfur dioxide was emitted in this step and no attempt was made to capture it.    Not far from Swansea, Henry Bessemer invented his revolutionary process in 1856 to  produce steel from pig iron by blowing air through the molten material. The process was conducted in a special reactor known as converter. In this process, the time to produce a batch of steel was reduced from few days to few minutes and at the same time the need to use fuel for making the transformation was eliminated. The copper industry adapted the sample principle few years later and as a result, the roast reaction was displaced by the conversion reaction.   Cu 2 S + O 2  → →  2 Cu + SO 2   The horizontal furnace   It is natural that metallurgists will treat rich ores first before they consider low-grade material because it is more economical. In the copper industry high-grade massive sulfide ores were broken down into small lumps and charged to a vertical furnace whereby the unwanted rock was removed as a slag and the copper-containing minerals were collected as a matte. When rich massive copper sulfide deposits became scarce, mining engineers turned to low-grade ores. This move coincided with the invention of the flotation process at the beginning of the twentieth century. Hence it became possible to obtain rich pulverised concentrates from low-grade ores. These concentrates, however, were not suitable for charging to the vertical furnace, since the charge would be blown out of the furnace when air was introduced at the lower part of the shaft. As a result, copper metallurgists turned their attention to adapting the same horizontal furnace that was used for the roast-reaction to melt the concentrates. This was the beginning of the era of the reverberatory furnace which has dominated the copper industry worldwide during the twentieth century.   While the vertical furnace is an excellent reactor: it is a heat exchanger as well as counter-current mass transfer reactor, the horizontal furnace suffers from the following disadvantages:   ·   Inefficient heat transfer since heat is mainly transferred by radiation from the roof, thus more fuel is burned unnecessarily.   ·   Excessive dust formation since the powdered concentrate is charged at right angles to the gas flow thus necessitating the installation of a large dust recovery system.   ·   Gases leaving the furnace are at high temperature necessitating the use of a bulky and expensive heat recovery system.   ·   The gases contain small amounts of SO 2  which cannot be economically recovered for making H 2 SO 4 , hence they are emitted in the atmosphere.    New smelting routes were developed, directed mainly towards energy economy. The most successful were the flash smelting process (Outokumpu Process), the bath smelting process (Noranda and INCO) and the continuous Mitsubishi Process. All these processes make use o oxygen or oxygen-enriched air instead of air and have several advantages:   ·   All the steps leading to the production of the raw metal are exothermic.   ·   Sulfur dioxide is produced in high concentrations and can be economically captured for
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