Extractive & Process Metallurgy: From Ore to Product

How metals are made and shaped. Learn mineral processing and extraction routes (pyro-, hydro- and electrometallurgy), Ellingham diagrams and reduction thermodynamics, ironmaking in the blast furnace and DRI, steelmaking (BOF, EAF, secondary refining, degassing), continuous casting, aluminium (Bayer + Hall–Héroult) and copper extraction, solidification and casting (nucleation, dendrites, segregation, Chvorinov's rule, risers, defects), metal forming (rolling, forging, extrusion, drawing, recrystallisation), powder metallurgy and green steel — with Python for Ellingham comparisons, aluminium electrolysis energy and solidification times.

Metals rarely occur pure — they are extracted from oxide, sulphide or carbonate ores, refined to remove impurities, alloyed and then cast and shaped. India is the world's second-largest steel producer, so ironmaking and steelmaking are core metallurgical engineering fields.

Metal production is energy- and carbon-intensive (steel alone ~7–8% of global CO₂), making process efficiency and green steel technologies urgent.

An analogy

Extracting iron is like convincing oxygen to leave iron for a more attractive partner: carbon (as CO) binds oxygen more strongly at high temperature, so it 'steals' oxygen from iron oxide, leaving metallic iron behind. The Ellingham diagram is the dating chart that shows who wins at which temperature.

Extraction routes

Three families:

Iron and steelmaking

Blast furnace: iron ore (pellets/sinter), coke and limestone; CO reduces Fe₂O₃ → Fe₃O₄ → FeO → Fe; produces hot metal (~4.5% C) and slag. Alternatives: DRI (gas-based, e.g. MIDREX) and coal-based sponge iron (common in India). Steelmaking: basic oxygen furnace blows O₂ to remove C, Si, Mn, P; electric arc furnace melts scrap/DRI. Secondary metallurgy (ladle furnace, vacuum degassing, desulphurisation, calcium treatment) sets chemistry and cleanliness; continuous casting produces slabs, blooms and billets.

Solidification and casting

Metals solidify by nucleation (homogeneous or on mould walls/inoculants) and dendritic growth; columnar and equiaxed zones form. Alloys segregate (solute rejected into remaining liquid). Shrinkage must be fed by risers that solidify last (Chvorinov). Defects: shrinkage porosity, gas porosity (H₂ in Al), hot tears, inclusions, cold shuts. Grain refiners (Ti–B in Al), modifiers (Sr in Al–Si) and controlled cooling improve quality.

Forming, powder metallurgy and green metallurgy

Hot working above the recrystallisation temperature (rolling, forging, extrusion) refines grains and closes porosity; cold working (drawing, cold rolling) strengthens by work hardening; thermo-mechanical controlled processing produces fine-grained micro-alloyed steels. Powder metallurgy (atomisation, pressing, sintering, HIP, metal injection moulding) makes near-net parts and feedstock for additive manufacturing. Decarbonisation: hydrogen-based DRI, EAF with renewable power, CCUS, higher scrap use, inert anodes for aluminium.

Formulas

Worked example: Faraday's law

Given: Copper electrorefining at 300 A for 24 h, η 95%

Find: Copper deposited.

Answer: 8.1 kg

Worked example: Chvorinov

Given: Casting modulus 1.5 cm, B = 2 min/cm²

Find: t_s.

Answer: 4.5 min

Worked example: Rolling reduction

Given: Slab 220 mm rolled to 3 mm strip

Find: Total reduction.

Answer: 98.6%

Ellingham check, aluminium energy and solidification time

# Process metallurgy: Ellingham check, Hall-Heroult energy, and Chvorinov solidification time
# Delta G (kJ per mol O2) = A + B*T for oxide formation (approximate linear fits)
reactions = {"2Fe + O2 -> 2FeO": (-530, 0.130), "2C + O2 -> 2CO": (-221, -0.179), "4/3Al + O2 -> 2/3Al2O3": (-1120, 0.214)}
for T in (900, 1500):
    vals = {r: a + b * T for r, (a, b) in reactions.items()}
    print(f"T = {T} K: " + ", ".join(f"{r.split()[-1]} {v:.0f}" for r, v in vals.items()))
print("carbon reduces FeO where the CO line lies below the FeO line (T above ~" +
      f"{(-530 + 221) / (-0.179 - 0.130):.0f} K); Al2O3 cannot be reduced by carbon at these temperatures")
# Aluminium electrolysis: charge and energy per tonne
F = 96485
mol_per_t = 1e6 / 26.98
charge = mol_per_t * 3 * F                    # C
V, eff = 4.2, 0.94                            # cell voltage, current efficiency
print(f"energy for 1 t Al: {charge*V/eff/3.6e6/1000:.1f} MWh")
# Chvorinov's rule: t = B (V/A)^2
B = 2.0                                       # min/cm2
for name, V, A in (("cube 10 cm", 1000, 600), ("plate 20x20x2 cm", 800, 960), ("riser cyl d=12,h=12", 1357, 679)):
    print(f"{name:20s}: modulus {V/A:.2f} cm, solidification {B*(V/A)**2:.1f} min")
# T = 900 K: 2FeO -413, 2CO -382, 2/3Al2O3 -927
# T = 1500 K: 2FeO -335, 2CO -490, 2/3Al2O3 -799
# carbon reduces FeO where the CO line lies below the FeO line (T above ~1000 K); Al2O3 cannot be reduced by carbon at these temperatures
# energy for 1 t Al: 13.3 MWh
# cube 10 cm          : modulus 1.67 cm, solidification 5.6 min
# plate 20x20x2 cm    : modulus 0.83 cm, solidification 1.4 min
# riser cyl d=12,h=12 : modulus 2.00 cm, solidification 8.0 min

Because the CO line slopes downward, carbon becomes a stronger reductant as temperature rises — above ~1000 K (with these approximate fits) it reduces iron oxide, which is why blast furnaces run hot. Alumina lies far below, so aluminium must be won by electrolysis — about 13 MWh per tonne, which is why aluminium smelters sit next to power plants and recycling saves ~95% of the energy. The riser has a larger modulus than the cube, so it solidifies last and feeds shrinkage.

Common mistakes

Applications

Key takeaways

Going further