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Pyrometallurgy

Pyrometallurgy uses high temperature — Ellingham diagrams show oxide stability; ΔG = ΔH − TΔS determines roast/smelting feasibility. Slag basicity B controls sulphur and metal losses in Indian copper and iron smelters.
Exam tip: keep SI units consistent end-to-end, write the governing relation symbolically before substituting, and sanity-check magnitude and sign.

Key formulas & points

Skim these first — then read the full notes below.

  • Roasting converts sulphide to oxide
  • Smelting separates metal from gangue
  • Reverberatory, blast furnace, flash smelting

Topic details

Introduction

Hindustan Copper and Vedanta smelters use flash smelting and converters — university extractive metallurgy follows Rosenqvist and Hartman flowsheets. Roasting exothermic for sulphides — SO₂ captured in acid plants per CPCB norms.

Scope in B.Tech and GATE syllabus

Ellingham diagram: plot ΔG° vs T for oxidation — lower line more stable oxide. Metal can reduce another's oxide if line crosses below.

Why this topic matters in practice

Slag basicity acidic vs basic affects viscosity and metal entrainment — exam questions on B calculation from charge composition.

Key relations & formulas

Formulas (Indian textbook notation)

  • ΔG=ΔH−TΔSfeasibility;ΔG<0spontaneous\Delta G = \Delta H - T\Delta S feasibility; \Delta G < 0 spontaneous

Formulas (Indian textbook notation)

  • EllinghamdiagrammetaloxidestabilityEllingham diagram metal oxide stability

Formulas (Indian textbook notation)

  • slagcompositionbasicityB=(CaO+MgO)(SiO2+Al2O3)slag composition basicity B = \frac{(CaO+MgO)}{(SiO_{2}+Al_{2}O_{3})}

Notation and sign conventions

Relation 1 —
ΔG=ΔH−TΔSfeasibility;ΔG<0spontaneous\Delta G = \Delta H - T\Delta S feasibility; \Delta G < 0 spontaneous

Formulas (Indian textbook notation)

  • ΔG=ΔH−TΔSfeasibility;ΔG<0spontaneous\Delta G = \Delta H - T\Delta S feasibility; \Delta G < 0 spontaneous
Write this relation with symbols exactly as in Rosenqvist Extractive Metallurgy — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 2 —
EllinghamdiagrammetaloxidestabilityEllingham diagram metal oxide stability

Formulas (Indian textbook notation)

  • EllinghamdiagrammetaloxidestabilityEllingham diagram metal oxide stability
Write this relation with symbols exactly as in Rosenqvist Extractive Metallurgy — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.
Relation 3 —
slagcompositionbasicityB=slag composition basicity B =

Formulas (Indian textbook notation)

  • slagcompositionbasicityB=(CaO+MgO)(SiO2+Al2O3)slag composition basicity B = \frac{(CaO+MgO)}{(SiO_{2}+Al_{2}O_{3})}
Write this relation with symbols exactly as in Rosenqvist Extractive Metallurgy — Standard reference before substituting numbers. Examiners award partial marks for a correct setup even when arithmetic slips.

Fundamentals and definitions

ΔG = ΔH − TΔS — negative ΔG spontaneous. High T favours entropy-driven reduction (ΔS > 0 for gas evolution). Ellingham slopes change at phase transitions — kinks on diagram.

Governing relations in practice

Roasting: 2Cu₂S + 3O₂ → 2Cu₂O + 2SO₂ — prepares for smelting. Partial roast for controlled sulphur retention.

Design and analysis considerations

Smelting: melt charge with flux — metal immiscible with slag. Blast furnace iron: coke reduces ore; slag CaO-SiO₂-Al₂O₃ system.

Advanced theory and extensions

Basicity B = (CaO+MgO)/(SiO₂+Al₂O₃) — B > 1 basic slag holds sulphur as sulphide in slag; too high B viscous slag, copper losses to slag in Cu smelting.

Assumptions and validity limits

State assumptions explicitly before using any relation for pyrometallurgy — steady state, uniform properties, linear elastic material, ideal gas, incompressible flow, etc., as applicable.
Wrong assumptions invalidate the entire solution even when the formula is correct. In Extractive Metallurgy viva and GATE descriptive questions, listing valid assumptions often earns separate marks.

Step-by-step problem approach

1. Read the question and list given data with SI units (common in Extractive Metallurgy papers).
2. Draw a neat labelled diagram where applicable — examiners in Indian universities award diagram marks even when arithmetic slips.
3. Identify which relation from this topic applies to pyrometallurgy.
4. Use equation 1:
ΔG=ΔH−TΔSfeasibility;ΔG<0spontaneous\Delta G = \Delta H - T\Delta S feasibility; \Delta G < 0 spontaneous
.
5. Use equation 2:
EllinghamdiagrammetaloxidestabilityEllingham diagram metal oxide stability
.
6. Substitute values, compute, and verify units and sign (direction).
7. State conclusion in one line — e.g. safe/unsafe, stable/unstable, feasible/infeasible.

Applications & exam relevance

Pyrometallurgy appears in smelters and refineries. In Indian mining curricula this topic is tested because it connects theory to pyro, hydro, and electrometallurgy.
GATE and semester exams often combine pyrometallurgy with earlier units — revise prerequisites before attempting mixed problems.
Industry interview panels sometimes ask: "Where did you use pyrometallurgy?" — answer with a lab, mini-project, or plant visit example if possible.

Common mistakes in exams

• Ellingham comparison at wrong temperature
• ΔG sign reversed for spontaneity
• Basicity missing Al₂O₃ amphoteric effect discussion
• Ignoring SO₂ environmental capture in mass balance

Quick revision checklist

Before attempting pyrometallurgy problems, confirm you can:
1. Roasting converts sulphide to oxide
2. Smelting separates metal from gangue
3. Reverberatory, blast furnace, flash smelting
Revise the solved examples in Rosenqvist Extractive Metallurgy — Standard reference and one previous-year GATE or university paper for this unit.

Worked examples

Try the problem first — open the solution when you are ready to check.

Guided practice — Pyrometallurgy

Problem

A standard Extractive Metallurgy numerical on pyrometallurgy supplies given data in SI units. Using ΔG = ΔH − TΔS feasibility; ΔG < 0 spontaneous and Ellingham diagram metal oxide stability, find the unknown quantity and state whether the result is physically reasonable.

Solution

1. List all given quantities with units (convert to SI if needed).
2. Draw a neat labelled diagram — diagram marks are common in Indian B.Tech papers.
3. Select
ΔG=ΔH−TΔSfeasibility;ΔG<0spontaneous\Delta G = \Delta H - T\Delta S feasibility; \Delta G < 0 spontaneous
and write it symbolically before substitution.
4. Substitute values, compute, and attach correct units.
5. Sanity-check: magnitude, sign, and direction must match pyro, hydro, and electrometallurgy.
Cross-check with solved examples in your Extractive Metallurgy textbook.

Conceptual check — Pyrometallurgy

Problem

In a Extractive Metallurgy semester or GATE paper you are asked: "State the main assumption, the governing relation, and one practical consequence of pyrometallurgy." What should a complete answer include?

📖 Standard books (India)

  • Rosenqvist Extractive Metallurgy — Standard reference

    Read: Syllabus unit

    Referenced in Indian B.Tech syllabus

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