Aguas Lluvias

Metals
Metallurgy How we get metals Bonding and structure of metals Alloys, composites Properties of metals and alloys Mechanical properties Electrical properties

OCCURRENCE OF METALS
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 = Be3Al2Si6O18 Hard to extract metals. 3) Nonsilicate MineralsOxides – Al2O3, TiO2, Fe2O3 Sulfides – PbS, ZnS, CuFeS2 Carbonates – CaCO3

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 ofthe metal.

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) + O2(g) + 2H2O(l) " 4[Au(CN)4]!(aq) + 4OH!(aq) Kf[Au(CN)2]! = 2x1038 The gold is then obtained by reduction: 2Au(CN)2!(aq) + Zn(s) " Zn(CN)42!(aq) + 2Au(s)Hydrometallurgy of Aluminum
• Aluminum is the second most useful metal. • Bauxite: Al2O3.xH2O. primary ore for Al impurities: SiO2 Fe2O3

Electrometallurgy
• Electrometallurgy is the process of obtaining metals through electrolysis. • Two different starting materials: molten salt or aqueous solution.

Bayer Process
• Bayer process: bauxite (~ 50 % Al2O3) is concentrated to produce aluminumoxide. • Dissolve bauxite in strong base (NaOH) at high T, P Al2O3 dissolves [Al(H2O)2(OH)4]!
hydrated metal complex

Electrometallurgy of Aluminum
Hall process electrolysis cell is used to produce aluminum.
Problem: Al2O3 melts at 2000°C and it is impractical to perform electrolysis on the molten salt. • Hall: use purified Al2O3 in molten cryolite (Na3AlF6, melting point 1012°C). Anode:C(s) + 2O2!(l) " CO2(g) + 4e! Cathode: 3e! + Al3+(l) " Al(l) • The graphite rods are consumed in the reaction.

• Filter out solids Fe2O3, SiO2 do not dissolve • Lower pH, Al(OH)3(s) precipitates Take advantage of amphoteric nature of Al

Electrometallurgy of Al
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 # 109J ofenergy.

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.

Pyrometallurgy
• • Pyrometallurgy: using high temperatures to obtain the free metal. Several steps are employed: Calcination is heating of ore to cause decompositionand elimination of a volatile product: PbCO3(s) " PbO(s) + CO2(g) Roasting is heating which causes chemical reactions between the ore and the furnace atmosphere: 1. Burns off organic matter. 2. Converts carbonates and sulfides to oxides: 2 ZnS(s)+ 3O2(g) "2ZnO(s) + SO2(g) 3. Less active metals are often reduced HgS(s) + O2(g) " Hg(l) + SO2(g)

The Pyrometallurgy of Iron
sources of iron:hematite Fe2O3 and magnetite Fe3O4. Iron Ore: Fe2O3 and SiO2

Add limestone and coke Coke is coal that has been heated to drive off the volatile components.

The blast furnace

Pyrometallurgy of Fe
Reactions
2C(s) + O2(g) " 2CO(g) + heat heat + C(s) + H2O(g) " CO(g) + H2(g) Fe3O4(s) + 4CO(g) " 3Fe(l) + 4CO2(g) Fe3O4(s) + 4H2(g) " 3Fe(l) + 4H2O(g) Coke: 1) heats furnace 2) reduces iron Why islimestone (CaCO3) added?

Pyrometallurgy of Fe
• At high T CaCO3 " CaO + CO2 CaO
oxide basic

+ SiO2 " CaSiO3(l)
slag oxide acidic

Metal + nonmetal "

Limestone (CaCO3) removes SiO2 (and other) impurities slag floats on Fe(l); protects it from oxidation by O2 Slag: cement cinder block building materials

Pyrometallurgy of Iron
• Product in blast furnace: pig iron brittle; not strong...