13Metallurgy_AlloysMJ

13Metallurgy_AlloysMJ - Metals Metallurgy How we get metals...

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Metals Metallurgy How we get metals Bonding and structure of metals Alloys, composites Properties of metals and alloys Mechanical properties Electrical properties Most metals are found in minerals. 1) Elemental Form e.g. Ag, Au, Pt – noble metals. 2) Aluminosilicates and Silicates Metal + Al, Si, O e.g. Beryl = Be 3 Al 2 Si 6 O 18 Hard to extract metals. 3) Nonsilicate Minerals Oxides – Al 2 O 3 , TiO 2 , Fe 2 O 3 Sulfides – PbS, ZnS, CuFeS 2 Carbonates – CaCO 3 OCCURRENCE OF METALS
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Steps in Metallurgy Steps in Metallurgy 1) Preliminary treatment to concentrate ore: Floatation. Hindered settling Magnetic separation 2) Further purification and reduction to obtain the metal in its elementary state: Hydrometallurgy – leaching. Pyrometallurgy – roasting, smelting. Electrometallurgy. 3) Final purification and refining of the metal. Hydrometallurgy Hydrometallurgy Metal is extracted from ore using aqueous reactions Leaching: a metal is selectively dissolved Dissolution agent: acid, base, salt. Example: Dissolve Au by forming complex ion with CN ! 4Au(s) + 8CN ! (aq) + O 2 (g) + 2H 2 O(l) " 4[Au(CN) 4 ] ! (aq) + 4OH ! (aq) K f [Au(CN) 2 ] ! = 2x10 38 The gold is then obtained by reduction: 2Au(CN) 2 ! ( aq ) + Zn( s ) " Zn(CN) 4 2 ! ( aq ) + 2Au( s )
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Hydrometallurgy of Aluminum Hydrometallurgy of Aluminum Aluminum is the second most useful metal. Bauxite: Al 2 O 3 . x H 2 O. primary ore for Al impurities: SiO 2 Fe 2 O 3 Bayer Process Bayer process: bauxite (~ 50 % Al 2 O 3 ) is concentrated to produce aluminum oxide. Dissolve bauxite in strong base (NaOH) at high T, P Al 2 O 3 dissolves [Al(H 2 O) 2 (OH) 4 ] ! hydrated metal complex Filter out solids Fe 2 O 3 , SiO 2 do not dissolve Lower pH, Al(OH) 3 (s) precipitates Take advantage of amphoteric nature of Al Electrometallurgy of Aluminum Hall process electrolysis cell is used to produce aluminum. Problem: Al 2 O 3 melts at 2000 ° C and it is impractical to perform electrolysis on the molten salt. Hall: use purified Al 2 O 3 in molten cryolite (Na 3 AlF 6 , melting point 1012 ° C). Anode: C( s ) + 2O 2 ! ( l ) " CO 2 ( g ) + 4e ! Cathode: 3e ! + Al 3+ ( l ) " Al( l ) The graphite rods are consumed in the reaction. Electrometallurgy Electrometallurgy is the process of obtaining metals through electrolysis. Two different starting materials: molten salt or aqueous solution .
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The Hall Process To produce 1000 kg of Al, we need 4000 kg of bauxite, 70 kg of cryolite, 450 kg of C anodes and 56 # 10 9 J of energy. Electrometallurgy Electrometallurgy of Al of Al Electrometallurgy Electrometallurgy Electrorefining of Copper • Because of its good conductivity, Cu is used to make electrical wiring. • Impurities reduce conductivity, therefore pure copper is required in the electronics industry.
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Pyrometallurgy: using high temperatures to obtain the free metal.
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