1) Elemental Forme.g. Ag, Au, Pt – noble metals.

2) Aluminosilicates and Silicates Metal + Al, Si, O

e.g. Beryl = Be3Al2Si6O18

Hard to extract metals.

3) Nonsilicate Minerals Oxides – Al2O3, TiO2, Fe2O3

Sulfides – PbS, ZnS, CuFeS2

Carbonates – CaCO3

OCCURRENCE OF METALS

MetallurgyMetallurgy the process of obtaining a metal from its ores

1) Preliminary treatment to concentrate ore:Floatation.Hindered settlingMagnetic 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.

HydrometallurgyHydrometallurgy

Metal is refined from ore using aqueous reactions

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)4] = 2x1038

Pure gold is then obtained by reduction:

2Au(CN)4(aq) + 3Zn(s) 3Zn2+(aq) + 8CN-(aq) + 2Au(s)

Similar process for silver (dissolves as [Ag(CN)2])

SILVERSILVER

Found as pure metal (Ag) or sulfide (Ag2S)

[Ag(CN)2] Kf = 1 x 1021

4Ag + 8CN(aq) + O2 + 2H2O 4[Ag(CN)2](aq) + 4OH(aq)

Ag2S + 4CN(aq) 2[Ag(CN)2](aq) + S2(aq)

Practice problem: Use Kf, with E0 and Ksp values (from tables) to calculate Keq for these reactions.

COPPERCOPPER

Copper containing ore (CuFeS2) is stirred with aqueous H2SO4 + O2

2CuFeS2(s)+2H+(aq)+SO42(aq) + 4O2(g)

2Cu2+(aq) + 2SO42-(aq) + Fe2O3(s) + 3S(s) + H2O

\ / 2CuSO4(aq)

Electrolyzed to Cu

Electrorefining of Copper• Slabs of impure Cu are used as anodes, thin sheets of

pure Cu are the cathodes.

• Acidic copper sulfate is used as the electrolyte.

• The voltage across the electrodes is designed to produce copper at the cathode.

• The metallic impurities do not plate out on the cathode.

• Metal ions are collected in the sludge at the bottom of the cell.

ElectrometallurgyElectrometallurgy

ElectrometallurgyElectrometallurgy

Hydrometallurgy of AluminumHydrometallurgy of Aluminum• Aluminum is the second most useful metal.• Bauxite: Al2O3.xH2O.

primary ore for Al

impurities: SiO2

Fe2O3

Bayer Process• Bayer process: bauxite (~ 50 % Al2O3) is concentrated to produce

aluminum oxide.• Dissolve bauxite in strong base (NaOH) at high T, P

Al2O3 dissolves [Al(H2O)2(OH)4]

hydrated metal complex

• Filter out solids

Fe2O3, SiO2 do not dissolve• Lower the pH so that Al(OH)3(s) precipitatesTakes advantage of the amphoteric nature of Al oxide.

Electrometallurgy of AluminumHall process is used to obtain aluminum metal.

Problem: Al2O3 melts at 2000C and it is impractical to perform electrolysis on the molten salt.

• Hall: use purified Al2O3 in molten cryolite (Na3AlF6, melting point 1012C).

Anode: C(s) + 2O2(l) CO2(g) + 4e

Cathode: 3e + Al3+(l) Al(l)• The graphite rods are consumed in the reaction.

Electrometallurgy of AlElectrometallurgy of Al

The Hall Process

Anode: C(s) + 2O2-(l) CO2(g) + 4e-

Cathode: Al3+(l) + 3e- Al(l)

Electrometallurgy of Sodium

Sodium is produced by electrolysis of molten NaCl.

CaCl2 is used to lower the melting point of NaCl from 804C to 600C.

At the cathode (iron): 2Na+(aq) + 2e 2Na(l)

At the anode (carbon): 2Cl-(aq) Cl2(g) + 2e

All metals in Groups I and II are obtained by molten salt electrolysis

• Pyrometallurgy: using high temperatures to obtain the free metal.

Calcination is heating of ore to eliminate a volatile product:

PbCO3(s) PbO(s) + CO2(g)

Roasting is oxidation of the ore:– Burns off organic matter.– 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)

PyrometallurgyPyrometallurgy

The Pyrometallurgy of Iron

• sources of iron:

hematite Fe2O3 and magnetite Fe3O4.

• Iron Ore: Iron oxides and SiO2

• Add limestone and coke

Coke is coal that has been heated to drive off the volatile components.

PyrometallurgyPyrometallurgy

Blast Furnace

Pyrometallurgy of FePyrometallurgy 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 furnace2) reduces iron

Why is limestone (CaCO3) added?

Pyrometallurgy of FePyrometallurgy of Fe• At high T

CaCO3 CaO + CO2

CaO + SiO2 CaSiO3(l) Metal + nonmetal slag oxide oxide

basic acidic

Limestone (CaCO3)

removes SiO2 (and other) impurities

slag floats on Fe(l); protects it from oxidation by O2

Slag: cementcinder blockbuilding materials

Physical Properties of Metals• Important physical properties of pure metals:

malleable, ductile, good conductors of heat and electricity.

• Metals are crystals in which every atom has 8 or 12 neighbors.

• There are not enough electrons for the metal atoms to make electron pair bonds to each neighbor.

Alloys: Mixtures of metals - often have improved physical properties

Metals and AlloysMetals and Alloys

ALLOYS1) Homogeneous (solution) alloys:

Mixed at the atomic level - one solid phase

2) Heterogeneous alloy:Non-homogeneous solid (e.g. pearlite steel has two phases: almost pure Fe and cementite, Fe3C).

3) Intermetallic alloys – compounds of two different metals having definite proportions:

e.g. Cr3Pt – razor blades. Ni3Al – jet engines, lightweight and strong. Co5Sm – permanent magnets in headsets. Au3Bi, Nb3Sn – superconductors

Homogeneous (solution) alloys

substitutional interstitial

Cr in Fe C in low-carbon steel

Two kinds:

Substitutional alloy – when one metal substitutes for another in the structure.

– metals must have similar atomic radii,– metals must have similar bonding characteristics.

Interstitial alloy – when a non-metal is present in the “holes” in a metal crystal lattice.– Interstitial atoms are smaller– The alloy is much stronger than the pure metal

(increased bonding between nonmetal and metal).– Example steel (contains up to 3 % carbon).

SOLUTION ALLOYS

Mechanical Properties of Metals and Alloys

Hypothetical situation:

Upon graduation, you go to work for Boeing.Your job – select a high-strength Al alloy for jet airplanes.

50 tons cargoAirplane: 500 tons } 150 tons plane structure

300 tons fuel

If you can triple the alloy strength, you can triple cargo load (to 150 tons).

Material Tensile Yield Stress (psi)pure (99.45%) annealed Al 4 x 103

pure (99.45%) cold drawn Al 24 x 103

Al alloy - precipitated, hardened 50 x 103 big improvement

But, “perfect” single crystal Al as a yield stress of ca. 106 psi!

Defects in Metallic Crystals

Defects are responsible for important mechanical properties of metals: malleability, yield stress, etc.

Non-directional bonding, large number of nearest neighbor atoms metallic structures readily tolerate “mistakes”

vacancy dislocation (missing atom) (extra plane of atoms) point defect line defect

Not important Very important

Dislocations Move Under Stress

Key point:

Moving a dislocation breaks/makes a line of metal-metal bonds (easy)

Shearing a perfect crystal means we have to break a plane of bonds (requires much more force)

shear force

Hardening of Alloys

Structural alloys - e.g., girders, knife blades, airplane wings

Need to minimize movement of dislocations. How?

1. Use annealed single crystals (expensive)Some specialty applications – e.g. jet turbine bladeImpossible for large items (airplane wings, bridges…)

• Work hardening - moves dislocations to grain boundaries

planar defect (stronger under

stress)

“Cold working” or “drawing” of a metal increases strength and brittleness (e.g., iron beams, knives, horseshoes)

Hardening of Alloys (contd.)

Work Hardening and Annealing have opposite effects

Annealing: crystal grains grow, dislocations move (metal becomes more malleable)

3. Alloying – homogeneous or heterogeneous Impurity atoms or phases “pin” dislocations.

Metal Crystal StructuresMetal Crystal Structures

Body-centered cubic (bcc)8 nearest neighborsNot close packed

Close packed(hexagonal or cubic)

hcp ccp

Malleability of Metals and Alloys

Some metals are soft and ductile (Au, Ag, Cu, Al, etc.)Others are hard (Fe, W, Cr, etc.) Why?

Crystal structure is important.

Two types: body centered cubic (bcc) - 8-coordinate - hard close packed (fcc and hcp) - 12-coordinate -

soft

Close-packed planes slip easily Non-close packed - “speed bumps”

Cu (fcc) CuZn alloy (brass) Zn (hcp)

http://www.its.caltech.edu/%7Evitreloy/development.htm

Amorphous (Glassy) Alloys

Metals are typically polycrystalline

Amorphous alloys have superior mechanical properties because dislocations cannot move.

Iron and Steels

Below 900oC, iron has bcc structure - “hard as nails”

Above 900oC, iron is close packed (fcc) - soft Can be worked into various shapes when hot

Steelmaking:Carbon steel contains ~ 1% C by weight (dissolves well in

fcc iron but not in bcc)

Slow cooling (tempering):fcc Fe/1%C mixture of bcc Fe and Fe3C (pearlite)

Fe3C (cementite) grains stop movement of dislocation in high carbon steel - very hard material

STEELSSTEELS

Steel: Fe (pig iron) + small amounts of C

Mild Steel: <0.2% C – malleable and ductileused in cables, nails, and chains.

Medium Steel: 0.2-0.6% C – toughused in girders and rails.

High Carbon Steel: 0.6-1.5% C – very toughused in knives, tools, and springs.

Stainless Steel:73% Fe, 18% Cr, 8% Ni, 1% C.