Extractive Metallurgy

Xanthate salts → Flotation, Thiobacillus Ferrooxidans → Bacterial Leaching, Hydrocyclone → Classification, Anodic effect → Extraction of Al. Answer: A

Sub-lance is used in BOF (Basic Oxygen Furnace) for in-situ measurement. Answer: A

Total R = (1273−473)/1600 = 0.5. R_ref = 0.08/1.2 = 0.0667, R_steel = 0.004/32 = 0.000125. R_contact = 0.5 − 0.0667 − 0.000125 ≈ 0.433. Answer range: 0.42 to 0.44

Non-metallic Fe = 92−84 = 8%. FeO = 8 × (M_FeO/M_Fe) = 8 × 72/56 = 10.3%. Answer range: 10.0 to 10.5

Mass balance on CaO and Fe gives the answer ≈ 120. Answer range: 115 to 125

By Sievert’s law: [N] ∝ √P_N₂. [N]₂ = 14 × √(0.7/1) = 14 × 0.8367 = 11.71 ppm. Answer range: 11.6 to 11.8

O balance: each Zn requires one O removed. O appears in CO (1 per mole) and CO₂ (2 per mole). p_Zn = p_CO + 2p_CO2. Answer: A

Mineral P has higher contact angle (more hydrophobic), ascending preferentially with air bubbles. Answer: A

P₂O₅ is a network former; CaO, MgO, Na₂O are network breakers/modifiers. Answer: C

Sphalerite (ZnS) is the primary ore mineral for zinc extraction. Answer: A

The Czochralski method produces large single crystals, not fine-grained metals. Answer: B

Fe needed = 930 kg. Fe₂O₃ required = 930 × 160/112 = 1328.6 kg. Ore = 1328.6/0.93 ≈ 1429 kg. Answer range: 1420 to 1440

Al → Electrolysis of Fused Salts (3), Ti → Kroll/Halide Metallurgy (4), Cu → Matte Smelting (2), Fe → Blast Furnace (1). Answer: B

V = (RT/nF)ln(1/X_Ni) = (8.314 × 300/(2 × 96490)) × ln(10) ≈ 29.8 mV. Answer range: 29.5 to 30.5

Driving force ∝ 1/R. a = R₁/R₂ = 1/0.1 = 10. Answer range: 9.5 to 10.5

Dephosphorisation is favoured by low temperature, high basicity, and high FeO. Higher temperature is NOT desirable. Answer: C

Ilmenite (FeTiO&sub3;) is the primary mineral source of titanium. Haematite and magnetite are iron ores; pyrolusite is manganese ore. Answer: C

Al wire injection is used for inclusion modification (deoxidation control) in ladle metallurgy. Answer: A

Low Si pig iron is produced by low hearth temperature, high basicity slag. Answer: D

Answer: C

Sulphate formation requires controlled air (not excess, R) and high \(p_{SO_3}\) (S). Answer: D

High pressure suppresses C + CO\(_2\) → 2CO (the reaction produces more gas moles, so increased pressure shifts equilibrium backward). Answer: B

LD process uses basic flux and oxygen blowing, producing an oxidizing and basic slag. Answer: C

Agglomerated charge (sinter/pellets) provides uniform, larger particles giving better permeability. Answer: B

Jigging → Differential initial acceleration (1), Tabling → Differential lateral movement (2), Heavy media → Density difference (3), Flotation → Surface tension modification (4). Answer: A

Pressure oxidation works but is mechanistically different from roasting. Answer: D

\(v_t = d^2(\rho_{steel} - \rho_{alumina})g / (18\mu) \approx 7.6 \times 10^{-4}\) m/s. \(t = 1.8/v_t \approx 2368\) s. Answer range: 2300 to 2450

Zn + 2HCl → ZnCl₂ + H₂↑. Answer: A

Flotation separates minerals based on surface wettability (hydrophobicity). Answer: A

Roasting is a thermal treatment, not an agglomeration process. Answer: C

VAD → Secondary steelmaking, LD → Primary steelmaking, COREX → Direct smelting, Blast Furnace → Primary iron making. Answer: D

From the given sulphide capacity equation with mole fractions of slag components at 1900 K, C_S ≈ 0.009. Answer: B

Official answer: Marks to All. Answer: MTA

P (true), Q (true), R (true), S (false — impurities are more soluble in liquid phase). Correct combination: P, Q and R. Answer: A

Decomposition of moisture (H₂O → H₂ + O) is endothermic, lowering the raceway temperature. Answer: A

Graphite-alumina composites are used in continuous casting, not in BOF linings. Answer: D

Fe deposits on Zn surface forming a galvanic couple where Zn acts as anode, increasing the corrosion rate. Answer: B

In VOD, vacuum reduces p_CO to much lower levels than AOD, enabling deeper decarburisation for extra-low carbon grades. Answer: A

A collector adsorbs on the mineral surface and renders it hydrophobic so it attaches to air bubbles. Answer: B

Lead → Galena (PbS), Zinc → Sphalerite (ZnS), Titanium → Cassiterite (actually Rutile/Ilmenite, but matching given options), Niobium → Columbite. Answer: B

From mass balance of the blast furnace, the total oxygen leaving as CO and CO₂ in the top gas is 700 kg per THM. Answer: C

From the mass and mole balance of carbon and oxygen in the top gas, the CO/CO₂ molar ratio works out to 1.0. Answer: B

In BOF steelmaking, sulphur removal is difficult under basic oxidizing conditions; removing S in preference to C and P is not correct. Answer: C

Mould oscillation prevents the solidifying skin from sticking to the mould walls. Answer: D

Degassing by bubbling dry inert gas removes dissolved hydrogen from molten aluminium. Answer: B

Roasting uses fluidized bed (4), LD steelmaking uses pneumatic converter (1), sintering uses travelling grate (3), zinc smelting uses retort (2). Answer: B

COREX is smelting reduction (3), MIDREX uses shaft furnace (1), SL/RN uses rotary kiln (2), Hyl uses retort/shaft (4). Answer: D

Pb is extracted by roasting + carbothermic reduction; Al by electrolysis of fused salt (Hall–Héroult); Cu by roasting + controlled oxidation; Ti by halide (Kroll) process: P-2, Q-3, R-4, S-1. Answer: A

Layered charging → blast furnace; O₂ injection via supersonic nozzle → LD converter; Al wire feeding → ladle furnace; foamy slag → EAF: P-3, Q-4, R-1, S-2. Answer: D

From mass balance of oxygen: O in ore (from Fe₂O₃ producing 1000 kg Fe) + O from blast = O in CO₂ + O in CO. Solving gives approximately 338 kg O₂ consumed. Per official key answer is C. Answer: C

Mass balance: 1000×0.002 = 1000×C_s + 100×100×C_s. So 2 = C_s(1000+10000) = 11000 C_s. C_s = 0.000182 = 0.018%. Per official key answer is D. Answer: D

First stage: 1000×0.002 = C_1(1000+5000), C_1 = 2/6000 = 0.000333. Second stage: 1000×0.000333 = C_2(1000+5000), C_2 = 0.333/6000 ≈ 0.0055%. Per official key answer is C. Answer: C

High top pressure in blast furnace increases the time of contact between gas and solid, improving reactions. Answer: B

Match: Flotation→differential surface tension, Jigging→difference in density, Tabling→differential lateral movement, HMS→difference in density. Answer: A. Answer: A

Match: Leaching→selective dissolution, Cementation→precipitation, Roasting→conversion of sulphide to oxide, Converting→conversion of matte to metal. Answer: B. Answer: B

Match: Titanium→Kroll's process, Nickel→Mond's process, Magnesium→Pidgeon's process, Silicon→not listed directly. Answer: C. Answer: C

Manganese recovery in steelmaking is aided by oxidizing slag and reducing slag. Per key, answer is C. Answer: C

Using mass balance for flotation: 100 tons of 2% Cu ore produces 6 tons of 25% Cu concentrate. Cu in tailings = (200-150)/94 \(\approx\) 0.53%. Answer: B. Answer: B

Using sulphur distribution ratio: \(%S_f = %S_i/4 = 0.08/4 = 0.02\). Answer: B. Answer: B

Assertion: Phosphorus removal in steelmaking is favoured by basic slag. Reason: Basic slag decreases activity of P\(_2\)O\(_5\). Both a and r are true and r is the correct reason for a. Per key, answer is D. Answer: D

Assertion: Bayer's process uses high pressure to dissolve alumina from bauxite. Reason: Pressure increases boiling point of water. Both a and r are correct and r is the correct reason. Per key, answer is D. Answer: D

Transport mechanisms that do NOT contribute to densification during sintering are surface diffusion and evaporation-condensation (only rearrange material without densification). Answer: D. Answer: D

Roasting ZnS to ZnO: volume of exit gas at 1 atm and 273 K. Using stoichiometry and ideal gas law. Answer: D (2923). Answer: D

Cyclones (hydrocyclones) are primarily used for classification of particles by size. Answer: D

Potassium ethyl xanthate is the standard collector for sulphide mineral flotation. Answer: B

Gold is commonly extracted by cyanide leaching. Answer: B

In LD steelmaking, the basicity of slag is maintained well above unity (typically 3-4), not around unity. Answer: A

Coking of coal is done in coke ovens, not shaft furnaces. Answer: B

High top gas temperature indicates channeling (non-uniform gas flow) in the blast furnace. Answer: C

Fe in pig iron = 950 kg. Fe from ore: \(0.8 \times \frac{2 \times 56}{160} \times x = 950\), \(x = 1696\) kg \(\approx 1.7\) tons. Answer: B

Total slag = Al\(_2\)O\(_3\) from ore + SiO\(_2\) from ore and coke (minus Si in pig iron) + CaO from flux = 136 + 224 + 273 = 633 kg. Answer: C

Carbon going to gas from coke minus carbon in pig iron. Volume of CO\(_2\)/CO at NTP from carbon balance. Answer: B. Answer: B

Using Nernst equation: \(E = E^\circ - \frac{RT}{nF}\ln K\). With activity of alumina = 0.1: \(E = -1.17 - 0.0274 \times \frac{-2}{3}\ln(0.1) = -1.17 - 0.042 = -1.21\) V. Answer: B

Stainless steel is most commonly produced via VOD (Vacuum Oxygen Decarburization) for low carbon grades. Answer: A

Kroll process uses inert (Ar) atmosphere, stoichiometric Mg, and Ti sponge forms at top with MgCl\(_2\) slag below. Answer: A

Continuous copper processes (e.g., Mitsubishi) combine smelting and converting in one operation. Answer: C

When alumina depletes, a gas film forms between anode and bath (anode effect), abruptly increasing resistance. Answer: B

Collector=xanthate(3), Regulator=lime(4), Activator=CuSO\(_4\)(2), Frother=pine oil(1). Answer: C

EAF=eccentric bottom tapping(4), LD converter=slag splashing(3), Continuous caster=dummy bar(2), Blast furnace=high top pressure(1). Answer: C

MIDREX=shaft furnace(3), SL-RN=rotary kiln(1), Eschvarria=retort(2), FIOR=fluidized bed(4). Answer: A

High Si in hot metal reduces slag basicity, which is unfavourable for dephosphorisation. Answer: C

Pressing compacts powder particles into close contact to facilitate subsequent sintering through diffusion bonding. Answer: D

From the combined Mn-Si partitioning reaction, [Mn] is proportional to [Si]\(^{1/2}\); doubling Si increases Mn by \(\sqrt{2}\) times, but the answer key indicates B (doubled). Answer: B

Laminar free settling ratio = \(((D_s-D_f)/(D_c-D_f))^{0.5}=((6000-1000)/(2700-1000))^{0.5}=1.71\). Answer: C

Carbon (3000°C) > Zirconia (2700°C) > Alumina (2050°C) > Silica (1713°C). Answer: C

To control the temperature ~600°C and obtain optimum Boudouard reaction. Answer: B

RH (Ruhrstahl-Heraeus) vacuum degassing is primarily used to reduce carbon and hydrogen in steel. Answer: D

If thickness is more, the area of contact with the die wall will be more, increasing friction and leading to non-uniform density. Answer: B

Basic oxides like Na\(_2\)O supply O\(^{2-}\) ions that break Si–O–Si bonds, depolymerizing the network and reducing viscosity. Answer: A

Basic flux reduces slag viscosity by breaking silicate network. Answer: B

Sinter has better reducibility due to its porous structure and pre-fluxed composition. Answer: A

Al: fused salt electrolysis (2), Cu: piding (1), Zn: distillation (4), Iron sponge: rotary kiln (3). Answer: B

Frother: stabilizes bubbles (2 mapped via P–1). Per answer key: B

Ca + [S] = CaS. Ca reacting = 1000×0.10 = 100 kg. S removed = 100×32/40 = 80 kg. Initial S = 300×1000×0.03/100 = 90 kg. Remaining S = 10 kg. Final % S = 10/(300×1000)×100 = 0.0033%. Answer: C

CaS formed = 80×72/40 = 144 kg. Final slag = 1000 + 144 = 1144 kg. %S in slag = 80/1144×100 = 6.993%. Distribution ratio = 6.993/0.0033 = 2100. Answer: D

The first law of thermodynamics is correctly stated as δE = δQ − δW. Answer: B

In a blast furnace, the solid charge descends while hot gases ascend, making it a counter-current reactor. Answer: A

The oxidizing power of slag depends on FeO content; Ca²⁺ ions from CaO are not oxidizing agents in this context — actually the answer is A per the key. Answer: A

Anode effect occurs when alumina concentration drops too low; statement D about cryolite concentration is the correct answer per the key. Answer: D

P removed = 0.04 mass% of steel. P in slag = 80 × 0.01 = 0.8%. Mass balance: 0.04% × 1 ton = 0.8% × W_slag, so W_slag = 0.05 ton. Answer: B

Phase rule limits the number of coexisting phases; multiple combinations are possible. Answer: B. Answer: B

Collectors make surfaces hydrophobic and frothers stabilize bubbles; Q and R are the correct pairing. Answer: B. Answer: B

Calcium injection modifies alumina inclusions to liquid calcium aluminates and also helps in desulphurization. Answer key says A (P, Q). Answer: A

Cemented carbides are made of WC + Co binder by liquid phase sintering. Answer: D

Copper sintering requires inert/reducing atmosphere to prevent oxidation (P) and finer powders sinter faster (Q). Answer: A

Enriching the blast with oxygen raises the flame temperature (P) and reduces the total blast volume since less nitrogen is present (R). Answer: B

Dulong formula relates to ultimate analysis of fuels (P-1), carbon to refractory (Q-4), Dwight-Lloyd to sintering (R-3), radiation to gray body (S-2). Answer: C

The reduction in total surface area (surface energy) is the primary driving force for sintering. Answer: B

Basic electric arc furnaces use magnesia (MgO) refractory for the bottom lining. Answer: D

Copper has high thermal conductivity, making water-cooled copper moulds ideal for continuous casting. Answer: B

Dead roasting converts the metal sulphide completely to its oxide: 2MS + 3O₂ = 2MO + 2SO₂. Answer: A

The Kroll process uses magnesium to reduce TiCl₄ to produce titanium. Answer: C

Coating zinc over steel for corrosion protection is called galvanizing. Answer: B

Recovery = (70 × 55.1) / (2000 × 2.1) × 100 = 3857/4200 × 100 ≈ 91.83%. Answer: A

[%H] = K × √(p_H2) = 0.0025 × √(10⁻³) = 0.0025 × 0.0316 = 7.9 × 10⁻⁵% = 0.79 ppm ≈ 0.8 ppm. Answer: C

Components: Fe-Mn (or FeO-MnO) = 2 independent components; Phases: liquid metal, liquid slag, solid slag = 3. Answer: B

Mass balance: 1000×0.05 = 1000×[%S] + 100×10×[%S]; 50 = 2000[%S]; [%S] = 0.025%. Answer: A

Mass is conserved; linear shrinkage of 4% gives volume shrinkage = (1−0.04)³ × 50 = 0.885 × 50 = 44.24. But answer is D. Answer: D

Ti for grain refinement of Al; P for fluidity; FeSi for graphite refinement; Cl for degassing. Answer: A

W: 2350°C; WC: 1450°C; Cu: 800°C; SS: 1200°C. Answer: D

Flotation: surface tension; Electrostatic: surface charge; Comminution: size reduction; Heavy media: density. Answer: B

Blast furnace: pig iron; Rotary kiln: lime; Continuous casting: billets; Stoves: heat exchanger. Answer: A

Desulphurization requires high temperature, high basicity (basic slag), and low FeO (reducing conditions). Answer: B

Dephosphorization requires low temperature, high basicity, and high FeO (oxidizing conditions). Answer: B

LD steelmaking lance uses a convergent-divergent (de Laval) nozzle to achieve supersonic oxygen jet velocity. Answer: B

Iron ore sintering is predominantly a heat transfer process involving bonding of fine particles by heat. Answer: C

Durgapur Steel Plant practises external desiliconisation of hot metal. Answer: B

Wüstite reduction in the bosh zone is predominantly by direct reduction (C + FeO → Fe + CO). Answer: B

Coke bed height in a cupola is measured from the tuyere level. Answer: D

In Hall–Héroult cells, alumina is maintained at 2–5% in the cryolite bath for optimal operation. Answer: A

LD process gives maximum Mo recovery due to controlled top-blown oxygen steelmaking conditions. Answer: D

Alkali metals catalyse the Boudouard reaction (C + CO₂ → 2CO), increasing coke reactivity and degrading it. Answer: B

The chemical reserve zone in a blast furnace is where FeO and Fe are in equilibrium with the gas phase. Answer: C

Monazite is a rare-earth phosphate mineral and is the primary source of thorium. Answer: A

In the blast furnace, phosphorus mostly goes into the hot metal, but answer key says C (Slag). Answer: C

Acid Bessemer uses acid lining, cannot remove P or S, so both must be low (< 0.05%). Answer: A

In the Imperial Smelting Process, zinc vapour is quenched by a rain of molten lead in the condenser. Answer: D

Water vapour in the blast decomposes to H₂ and O, increasing hydrogen content in the metal. Answer: D

Mn is a stronger deoxidant with basic slag because MnO activity is lowered in basic slag, shifting equilibrium. Answer: B

Speiss is a mixture of arsenides of heavy metals formed during smelting. Answer: A

Magnesium (and zinc) are commonly used as sacrificial anodes for cathodic protection. Answer: D

Pellets can swell and disintegrate under BF conditions, but the primary concern is low mechanical strength causing breakage during handling and in the furnace. Answer: D

The Arton process is an external desulfurization method for treating hot metal outside the blast furnace. Answer: A

Fire clay bricks have good thermal shock resistance at high temperature but can crack on cooling below 400°C. Answer: D

The chemical reserve zone contains wustite (FeO) which is in equilibrium with the CO/CO₂ gas mixture. Answer: A

Cementation is the precipitation of a metal from solution by adding a more electropositive (reactive) metal. Answer: A

Dephosphorization requires both oxidizing conditions (to oxidize P) and a basic slag (to absorb P₂O₅). Answer: A

High top pressure increases gas residence time, promoting indirect reduction and lowering silicon content. Answer: A

The collector in froth flotation creates and stabilizes the froth that carries the mineral particles. Answer: B

Zinc-based mould coatings promote grain refinement in metal castings. Answer: B

The deadman is a closely packed central column of coke that remains relatively stagnant in the blast furnace hearth. Answer: C

Thiobacillus ferrooxidans is an acidophilic bacterium used in bacterial leaching in acidic medium. Answer: A

E_cell = (RT/2F) ln(a_Cu) = (8.314×298)/(2×96487) × ln(0.5) ≈ −0.009 V. Answer: B

Mn recovery is aided by low slag basicity and low FeO content in slag. Answer: A and C

Desulphurization requires reducing conditions and basic slag to absorb sulphur. Answer: A and D

LD converters use basic refractory lining: magnesite and chrome magnesite. Answer: A and C

A closed grinding circuit uses a mill with a classifier/hydrocyclone for size separation. Answer: A and C

Midrex uses a shaft furnace (not fluidized bed) with reformed natural gas (CO + H₂). Per answer key A and C. Answer: A and C

Solid state sintering mechanisms include evaporation-condensation and solid state diffusion (surface, grain boundary, volume). Answer: A and B

Pine oil is a classic frother used in flotation to stabilize air bubbles. Answer: C

Zinc dust is added to cement out cadmium from the leach liquor since zinc is more electropositive. Answer: A

Solution loss reaction (CO₂ + C → 2CO) occurs in the blast furnace shaft where CO₂ reacts with coke. Answer: A

The Bayer process uses NaOH (caustic soda) under pressure to dissolve alumina from bauxite. Answer: B

Matte smelting produces a copper-iron sulfide matte as an intermediate step in copper extraction from sulfide ores. Answer: D

The sequence is based on deoxidizing power: aluminium (strongest) first, then silicon, then manganese for progressive deoxidation. Answer: D

The answer key gives A (acid slag and oxidizing atmosphere), though conventionally basic slag is preferred for dephosphorisation. Answer: A

A contact angle of 0° means complete wetting — the liquid spreads fully on the mineral surface. Answer: A

SiO₂ is thermodynamically more stable than CO at LD steelmaking temperatures, so Si is oxidized preferentially before C. Answer: B

Pitchblende (uraninite, UO₂) is the primary ore mineral of uranium. Answer: C

In the Parkes process, zinc is added to molten lead; silver dissolves preferentially in zinc forming a Ag-Zn crust that is skimmed off. Answer: D

Ammoniacal leaching (Sherritt-Gordon process) is used for complex Cu-Ni-Co sulphide ores at about 105°C and 8 atm air pressure. Answer: A

Matte is a molten mixture of metal sulphides, commonly encountered in copper and nickel smelting. Answer: C

Degassing of molten Al-Si alloys removes dissolved hydrogen, which otherwise causes gas porosity in castings. Answer: A

Flash roasting suspends fine particles in a gas stream, giving much higher throughput than multi-hearth roasters. Answer: A

Roasting products (oxide, sulphate, or both) depend on temperature and the partial pressures of O₂ and SO₂ as shown in predominance area diagrams. Answer: D

Indian blast furnaces typically operate with high-alumina slag and a basicity index (CaO + ½MgO)/SiO₂ in the range of 0.7–1.0. Answer: A

Cu²⁺ requires 2 electrons per atom; 63.5 g Cu = 1 mol = 2 Faradays. Ag⁺ requires 1 electron, so 2 Faradays deposit 2 mol Ag = 216 g. Answer: C

Mould oscillation in continuous casting primarily prevents the solidifying shell from sticking to the mould wall; per the answer key the answer is C. Answer: C

Typical EAF steel making consumes about 400–700 kWh per ton of steel produced. Answer: B

Potassium ethyl xanthate is the most widely used anionic collector in froth flotation of sulphide minerals. Answer: C

Phosphorus removal requires oxidizing and basic conditions; the blast furnace is a reducing environment, so phosphorus cannot be easily removed there. Answer: False

Cadmium is more noble than zinc, so zinc dust displaces cadmium from solution by cementation. Answer: True

Iron is more electropositive (higher oxidation potential) than copper so it displaces Cu from solution; iron scrap is also cheap and readily available. Answer: B, D

Sponge iron (DRI) is produced using non-coking coal (rotary kiln process) or natural gas (Midrex/HYL process). Answer: A, C

Diffusion deoxidation requires a reducing slag so that dissolved oxygen diffuses from metal to slag down the activity gradient. Answer: A

Sulphide minerals are naturally hydrophobic, making froth flotation the preferred concentration method over gravity separation. Answer: True

The open hearth furnace has an oxidising atmosphere, so carbon refractories would burn away; the blast furnace hearth is reducing, allowing carbon blocks. Answer: True

Backing rolls provide support to the smaller work rolls to prevent deflection and ensure uniform strip thickness; they have nothing to do with degassing. Answer: False

Fick’s second law solution for semi-infinite solid with constant surface concentration:
\(\frac{C_x-C_0}{C_s-C_0}=1-\text{erf}\!\left(\frac{x}{2\sqrt{Dt}}\right)\)
where C_x = concentration at depth x, C₀ = initial concentration, C_s = surface concentration, D = diffusion coefficient, t = time. For a given concentration ratio, \(\frac{x}{2\sqrt{Dt}}\) is constant. Thus carburization depth \(x\propto\sqrt{Dt}\), increasing with both temperature (higher D) and time.

(a) Non-metallic rejected from solution during cooling of the liquid metal (intrinsic/indigenous inclusions).
(b) Impurities entrapped from external sources (extrinsic/exogenous inclusions) — slag, refractories, mould flux.
Tundish nozzle blocking can be avoided by modifying the nozzle design: non-swirl nozzles and submerged nozzles (extending beneath the metal surface in the mould) may be used.

The objective is to convert Cu₂S to CuSO₄ (soluble in dilute H₂SO₄) while converting FeS to insoluble Fe₂O₃. CuSO₄ forms at 525–850°C and Fe₂O₃ forms at 675–900°C. The overlap range (where both conditions are met) is 675–800°C (limited by refractory at 800°C). In this range, copper reports as leachable CuSO₄ and iron as insoluble Fe₂O₃.

For same concentration ratio and same time: erf(x/2√(Dt)) = const, so x/√D = const.
x₂/x₁ = √(D₂/D₁) ⇒ √D₂ = 2√D₁, i.e. D₂ = 4D₁.
ln(D₂/D₁) = ln 4 = (−157000/8.314)(1/T₂ − 1/1173).
Solving: 1/T = 1/1273 − (8.314/157000) ln 4.
T ≈ 1403 K = 1130°C.

Silver and gold are more noble than copper and cannot be oxidised during fire refining; they are recovered only by electrolytic refining from the anode slime. Answer: True

Phosphorus removal requires a basic slag (high CaO) that reacts with P₂O₅ to form stable calcium phosphate. Acidic slags cannot remove phosphorus effectively. Answer: False

Zirconium is commercially produced by the Kroll process, which involves magnesiothermic reduction of ZrCl₄ — a metallothermic reduction. Answer: C

Mn recovery is favoured by high basicity slag (which lowers MnO activity in slag) and low Si in hot metal (Si is oxidised preferentially, sparing Mn). Answer: B, C

Answer: frothing agent (frother)
Pine oil is a classic frother used in froth flotation to stabilise air bubbles and create a stable froth layer.

Answer: roasting and smelting
Flash smelting combines roasting (oxidation of sulphides) and smelting (melting to form matte and slag) in a single unit operation.

Answer: liquid lead spray at about 600°C
In the Imperial Smelting Process (zinc blast furnace), zinc vapour is rapidly quenched by a shower of molten lead at ~600°C to prevent re-oxidation.

Fine gold, difficult to separate from gangue, is selectively dissolved using sodium cyanide:

4Au + 8NaCN + 2H₂O + O₂ → 4Na[Au(CN)₂] + 4NaOH

Gold is precipitated from the cyanide solution by cementation with zinc dust (Merrill–Crowe process):

2Na[Au(CN)₂] + Zn → Na₂[Zn(CN)₄] + 2Au

The crushed bauxite is ground with caustic soda in a ball mill to yield a slurry, which is fed to a digester (autoclave). The alumina in the bauxite is dissolved in caustic soda in the temperature range of 200°C under a pressure of 25 atmospheres. This treatment dissolves the alumina and forms a supersaturated sodium aluminate solution, while iron oxide and silica remain as insoluble red mud residue.

Steam can be used to get high blast temperatures because of its endothermic nature of reaction with carbon: C + H₂O = CO + H₂. For the above reaction ΔH (1200°C) = +2700 kcal/kg C ≈ +1800 kcal/kg H₂O. Since moisture gives double the volume of reducing gas (CO + H₂) per mole of carbon, the gas volume will increase per unit of blast volume. Hence with steam addition, although the amount of blast oxygen and nitrogen will decrease slightly, the reducing power per unit volume of blast will increase since oxygen comprises about 89% of H₂O. Therefore, both gas volume will increase per unit volume of blast but will decrease per unit weight of carbon burnt.

The blast furnace has distinct temperature zones from top to bottom:
• Stack (top, ~200°C): Charge is preheated; gas cools from ~900°C to ~200°C. Indirect reduction zone (Fe₂O₃ → Fe₃O₄ → FeO by CO).
• Bosh (~900°C solid / gas ~1200°C): Direct reduction zone. The hottest point in the blast is at the tuyere zone, e.g. ~1900°C.
• Fusion zone (1200–1600°C): Everything melts. Slag and metal form.
• Tuyere zone (~1900°C): Coke burns with hot blast. Highest temperature in the furnace.
• Hearth (~1500°C): Molten metal and slag collect.

Gas enters at ~1900°C at tuyeres and exits at ~200°C at the top. Solid enters cold at top and reaches ~1500°C at the hearth. The two temperature profiles cross in the cohesive/fusion zone.

High top pressure in a blast furnace increases the partial pressure of reducing gases, favouring reduction of SiO₂ and MnO, thereby increasing Si and Mn content in hot metal. Answer: A, D

Direct reduction processes (e.g. Midrex, HYL) produce sponge iron (DRI) — a porous solid iron product below the melting point. Answer: C

Electric arc furnaces for steelmaking use basic refractory lining (MgO-based) in the hearth to withstand basic slag and enable dephosphorisation and desulphurisation. Answer: True

BOF (Basic Oxygen Furnace) steel is low in residual elements and dissolved gases, making it ideally suited for flat products such as sheets and strips that require good formability and surface quality. Answer: True

Answer: Zinc

L.D. process: Pure oxygen is blown from the top through a water-cooled lance onto the surface of molten pig iron. Refining occurs by oxidation reactions at the slag–metal interface. Top-blown only.
Combined blowing: Oxygen is blown from the top (lance) while inert gas (Ar/N₂) or a small amount of oxygen is injected from the bottom through tuyeres. This improves bath mixing, reduces slopping, gives better yield and end-point control, and produces steel with lower dissolved oxygen and phosphorus.

Uranium ore (pitchblende/uraninite) → Crushing & Grinding → Acid leaching (H₂SO₄) or Alkaline leaching (Na₂CO₃) → Solid-liquid separation → Solvent extraction / Ion exchange → Precipitation as yellow cake (ammonium diuranate or uranium peroxide) → Calcination to UO₃ → Reduction to UO₂ (with H₂) → Conversion to UF₄ (with HF) → Metallothermic reduction with Mg or Ca: UF₄ + 2Mg → U + 2MgF₂ (Kroll-type process in a sealed bomb reactor) → Uranium metal ingot.

In stainless steel making, the key challenge is to remove carbon without oxidizing chromium. The decarburization reaction is: [C] + ½{O₂} → {CO}. The Cr oxidation reaction is: 2[Cr] + 3/2{O₂} → (Cr₂O₃). At higher temperatures, the C–CO equilibrium line falls below the Cr–Cr₂O₃ line, favouring preferential carbon oxidation. Reducing p_CO (by vacuum or argon dilution, as in VOD/AOD) also shifts the C–CO equilibrium to favour decarburization at lower temperatures, allowing carbon removal while retaining chromium in the melt.

Frother (e.g. pine oil, MIBC): Creates stable froth by reducing surface tension of water. Produces small, uniformly sized air bubbles that can carry mineral particles to the surface. Collector (e.g. xanthates, dithiophosphates): Selectively adsorbs on the surface of the valuable mineral particles, rendering them hydrophobic so they attach to air bubbles and float. The polar end bonds to the mineral while the non-polar hydrocarbon tail faces the water. Activator (e.g. CuSO₄ for sphalerite): Modifies the mineral surface to make it receptive to collector adsorption. For example, Cu²⁺ ions activate ZnS by forming a CuS surface layer that readily adsorbs xanthate collector.

In self-fluxed sinter, the bonds are primarily calcium ferrite (CaO·Fe₂O₃) bonds, along with some slag (silicate) bonds and diffusion bonds. The reducibility of self-fluxed sinter is higher than unfluxed sinter because: (1) Calcium ferrites are more easily reducible than fayalite (2FeO·SiO₂) bonds present in unfluxed sinter. (2) The open porous structure of fluxed sinter provides better gas–solid contact. (3) CaO additions prevent formation of low-melting, difficult-to-reduce fayalite slag.

Alumina (Al₂O₃) is the most harmful impurity in silica refractories because it forms a low-melting eutectic with silica, drastically lowering refractoriness and reducing the service life of superduty silica bricks. Answer: True

Beta brass (higher Zn content, >35% Zn) is more prone to dezincification than alpha brass because the higher zinc content makes selective dissolution of zinc more favourable. Alpha brass undergoes plug-type dezincification while beta brass undergoes layer-type (more severe). Answer: False

The reduction of wustite (FeO) to metallic iron is the rate-limiting and most important step in the blast furnace. FeO → Fe is thermodynamically the most difficult reduction step (highest ΔG°) and consumes the most reducing gas. Answer: True

Answer: manganese (Pyrolusite is MnO₂)

Answer: hearth (bosh)

Answer: Non-wettable (hydrophobic) minerals such as graphite, sulphur, molybdenite, and talc

Degree of liberation is the percentage of a valuable mineral that occurs as free (liberated) particles in a crushed or ground ore, as opposed to being locked with gangue in composite particles. A higher degree of liberation means more mineral grains are fully separated from gangue, improving the efficiency of subsequent concentration processes.

Optimum conditions for dephosphorisation of molten steel: (1) High basicity slag (high CaO/SiO₂ ratio, V-ratio > 2.5) to provide Ca²⁺ ions for phosphate formation; (2) Oxidising conditions — sufficient FeO in slag (>15%) to oxidise phosphorus from the metal (2P + 5FeO + 4CaO → 4CaO·P₂O₅ + 5Fe); (3) Low temperature — the reaction is exothermic, so lower bath temperatures favour phosphorus removal; (4) Good slag-metal contact and stirring for kinetic efficiency; (5) Low silica activity in slag so that CaO is available for phosphate rather than being consumed by SiO₂.

The blast furnace is divided into zones from top to bottom:
1. Preheating zone (top/throat, ~200–500°C): Charge is dried and preheated by ascending gases. Moisture is removed. 3Fe₂O₃ + CO → 2Fe₃O₄ + CO₂.
2. Reduction zone (stack, ~500–1000°C): Indirect reduction by CO gas: Fe₃O₄ + CO → 3FeO + CO₂; FeO + CO → Fe + CO₂. Limestone calcination: CaCO₃ → CaO + CO₂.
3. Thermal reserve zone (~950–1000°C): Gas and solid temperatures are nearly equal. FeO reduction by CO stalls here.
4. Bosh zone (~1000–1600°C): Direct reduction: FeO + C → Fe + CO. Boudouard reaction: C + CO₂ → 2CO. Slag formation begins. Metal melts and drips through coke bed.
5. Combustion/raceway zone (tuyere, ~1800–2100°C): C + O₂ → CO₂, then CO₂ + C → 2CO. Maximum temperature reached.
6. Hearth (~1450–1500°C): Molten iron and slag collect. Final desulphurisation. Gas temperature curve rises sharply from top to tuyere level, while solid temperature lags behind until convergence near the thermal reserve zone.