[D1] PYRO MERGED

Iron Smelting: Blast Furnace Operation and Reactions

• Blast Furnace Construction & Operating Principle:

  • The primary purpose of a blast furnace is to reduce and convert iron oxides into liquid iron (pig iron).

  • Physical Structure: A tall, vertical steel stack approximately $30\,m$ in height, lined internally with refractory firebrick and carbon brick at the hearth.

  • Operational Mode: Continuous counter-current reactor. Solid charge materials (iron ore, coke, and limestone) are loaded at the top shaft, while preheated air is blasted in near the bottom above the slag level (bosh) via water-cooled nozzles called tuyeres.

• Composition of the Charge (Burden):

  • Primary Feed (Iron Ore):

  • Consists of iron oxides ($Fe_2O_3$, $Fe_3O_4$).

  • Raw Ore: Contains $50\,\%\text{ to }70\,\%\text{ Fe}$.

  • Iron Ore Pellets: Agglomerated spheres measuring $0.5\text{ to }1.5\,\text{inches}$ in diameter.

  • Sinter: Contains $60\,\%\text{ to }65\,\%\text{ Fe}$. Formed by fusing very fine iron ore, steel plant waste, fine coke, and fine limestone into pieces sized $0.5\text{ to }2.0\,\text{inches}$.

  • Fluxes (Slag Fixers):

  • Added to remove sulfur, lower the melting point of the burden, and produce a high-fluidity slag.

  • Limestone ($CaCO_3$): Includes calcium limestone and dolomitic limestone (high in magnesia, $MgO$).

  • Silica Sand ($SiO_2$): Introduced naturally as gangue associated with the iron ore.

  • Fuel / Reductant:

  • Coke: Sized in $1\text{ to }4\,\text{inch}$ pieces; contains $90\,\%\text{ to }93\,\%$ fixed carbon. Provides high compressive strength to support the burden column and maintains high gas permeability.

  • Air Blast:

  • Oxygen source for combustion; preheated to approximately $1200\,^\circ\text{C}$. Can be stoichiometric air or enriched with oxygen up to $30\,\%$.

• Internal Temperature Profile & Thermal Zones:

  • Flue Gas Exit Temperature: $150\,^\circ\text{C}\text{ to }200\,^\circ\text{C}$.

  • Shaft / Stack Temperature Profile: Increases from ambient at the top to $130\,^\circ\text{C}$, $200\,^\circ\text{C}$, $300\,^\circ\text{C}$, $700\,^\circ\text{C}$, up to the Thermal Reserve Zone at $900\,^\circ\text{C}\text{ to }1150\,^\circ\text{C}$.

  • Iron Formation Zone: Iron forms and trickles down at approximately $400\,^\circ\text{C}$.

  • Carbon Monoxide Formation Zone: $CO$ forms and rises at approximately $800\,^\circ\text{C}$.

  • Carbon Dioxide Formation Zone: $CO_2$ forms and rises at approximately $1400\,^\circ\text{C}$.

  • Bosh / Combustion Zone: Maximum localized temperature reaches $1600\,^\circ\text{C}\text{ to }2100\,^\circ\text{C}$.

  • Hearth Zone: Liquid pig iron temperature is $1475\,^\circ\text{C}\text{ to }1500\,^\circ\text{C}$; molten slag temperature is $>1500\,^\circ\text{C}$ ($1500\,^\circ\text{C}\text{ to }1550\,^\circ\text{C}$).

• Chemical Reactions in the Blast Furnace:

  • Primary Iron Reduction Reactions (Step-wise Reduction by $CO$):

  • At $T = 450\,^\circ\text{C}$:       $2Fe_2O_3 + CO \rightarrow CO_2 + 2Fe_3O_4$

  • At $T = 800\,^\circ\text{C}$:       $Fe_3O_4 + CO \rightarrow CO_2 + 3FeO$

  • At $T = 1200\,^\circ\text{C}$:       $FeO + CO \rightarrow CO_2 + Fe$

  • Slag Formation Reactions:

  • Calcination of flux at $T = 850\,^\circ\text{C}$:       $CaCO_3 \rightarrow CaO + CO_2$

  • Silicate slag formation at $T = 1000\,^\circ\text{C}$:       $CaO + SiO_2 \rightarrow CaSiO_3$

  • Sulfur Removal Reaction:

  • Occurs at $T = 1000\,^\circ\text{C}$:       $FeS + CaO + C \rightarrow CaS + FeO + CO$

  • Direct Reduction of Pig Iron Impurities:

  • Reduction of silica at $T = 1500\,^\circ\text{C}$:       $SiO_2 + 2C \rightarrow Si + 2CO$

  • Reduction of manganese oxide at $T = 1100\,^\circ\text{C}$:       $MnO + C \rightarrow Mn + CO$

  • Reduction of phosphorus pentoxide at $T = 1000\,^\circ\text{C}$:       $P_2O_5 + 5C \rightarrow 2P + 5CO$

  • Combustion & Boudouard Reactions:

  • Direct oxidation of carbon at $T = 450\,^\circ\text{C}$:       $C + O_2 \rightarrow CO_2$

  • Partial combustion / gasification at $T = 900\,^\circ\text{C}\text{ to }1200\,^\circ\text{C}$:       $C + CO_2 \rightarrow 2CO$

  • Boudouard Equilibrium Equation (valid from $500\text{ to }2200\,\text{K}$):       $\log(K) = \frac{9141}{T} + 0.0002247\,T - 9.595$       Note: $\log(K) = 0$ at $T = 975\,\text{K}$.

  • Wustite ($Fe_{0.947}O$) Reduction Zone:

  • At approximately $1000\,^\circ\text{C}$, the equilibrium gas concentration for wustite reduction is $60\,\%\text{ CO}$ and $40\,\%\text{ CO}_2$.

• Slag Control and Basicity Ratio:

  • The Slag Basicity Ratio is defined as:     $\text{Basicity Ratio} = \frac{\text{CaO} + \text{MgO}}{\text{SiO}_2 + \text{Al}_2\text{O}_3}$

  • In blast furnace operations, this ratio is maintained between $0.9\text{ and }1.1$ to ensure:

  • Slag remains sufficiently molten and fluid at Critical Process Temperature ($CPT = 1500\,^\circ\text{C}$).

  • All gangue minerals and coke ash report entirely to the slag.

  • Alkalis ($K_2O$ and $Na_2O$) do not accumulate inside the furnace shaft.

  • Maximum sulfur absorption is achieved via calcium combination ($CaS$).

• Typical Product Chemical Analysis:

  • Pig Iron: $Fe = 93\text{--}95\,\%$, $C = 4.1\text{--}4.4\,\%$, $Mn = 0.55\text{--}0.75\,\%$, $Si = 0.30\text{--}0.90\,\%$, $P = 0.03\text{--}0.09\,\%$, $S = 0.025\text{--}0.050\,\%$, $Ti = 0.02\text{--}0.06\,\%$.

  • Slag: $CaO = 40\,\%$, $SiO_2 = 38\,\%$, $Al_2O_3 = 10\,\%$, $MgO = 10\,\%$, $S = 0.8\,\%$, $TiO_2 = 0.5\,\%$, $MnO = 0.4\,\%$, $Fe = 0.2\,\%$ (entrained metallic droplets and oxides combined), $P_2O_5 = <0.1\,\%$.

  • Blast Furnace Flue Gas: $N_2 = 49\,\%$, $CO_2 = 23\,\%$, $CO = 22\,\%$, $H_2 = 3\,\%$, $H_2O = 3\,\%$.

• Typical Blast Furnace Material Balance Benchmark:

  • Input Burden: $100\,\text{tons}$ Iron Ore ($50\,\%\text{ Fe}$, $8\,\%\text{ SiO}_2$, $3\,\%\text{ Al}_2\text{O}_3$) + $50\,\text{tons}$ Coke + $25\,\text{tons}$ Limestone + Air Blast.

  • Output Products: $54\,\text{tons}$ Pig Iron ($94\,\%\text{ Fe}$, $4\,\%\text{ C}$, $1\,\%\text{ Si}$) + $30\,\text{tons}$ Slag ($45\,\%\text{ CaO}$, $32\,\%\text{ SiO}_2$, $15\,\%\text{ Al}_2\text{O}_3$) + Blast Furnace Flue Gas (used as plant fuel).

• Auxiliary Systems:

  • Cowper Stove: Regenerative heat exchanger that preheats the incoming cold air blast to $\sim 1200\,^\circ\text{C}$ by burning blast furnace exhaust gas through refractory checker brickwork.

  • Tuyeres & Goosenecks: Water-cooled copper nozzles injecting hot blast air and auxiliary fuels into the bosh.

  • Torpedo Ladle: Refractory-lined rail car used to transport liquid pig iron from the blast furnace taphole to the steelmaking shop.

Steelmaking: Basic Oxygen Process (BOP / BOF)

• General Sequential Steelmaking Steps:

  1. Desulfurization in the Ladle: Powdered $CaO$, $CaC_2$, and/or $Mg$ are injected into the molten pig iron. Sulfur reacts exothermically to form a molten $CaO$-, $MgO$-, and $S$--rich slag, which is raked off.

  2. Basic Oxygen Refining (BOF/BOS): Molten iron is oxidized with virtually pure $O_2$ and fluxed with $CaO$ and $MgO$ to eliminate $Si$, $C$, $S$, and $P$.

  3. Alloying: Addition of alloying elements ($Mn$, $Cr$, $Ni$, $V$, $Mo$) in the ladle.

  4. Degassing: Vacuum treatment to eliminate dissolved $H_2$ and $N_2$ gases and adjust carbon levels.

  5. Continuous Casting: Solidification into slabs, billets, or blooms.

  6. Finishing: Mechanical shaping via hot-rolling or cold-rolling.

• Principles of Basic Oxygen Refining:

  • The term "Basic" refers to the chemical nature of the lime/dolomite fluxed slag ($CaO$, $MgO$), which enables the removal of phosphorus and sulfur alongside carbon, silicon, and manganese.

  • Superiority over the historic Bessemer Process: Uses $99\,\%$ pure oxygen instead of air, preventing nitrogen absorption and nitrogen-based embrittlement in the steel.

  • The process is autogenous: No external fuel is required. Thermal energy is generated internally by the intense exothermic oxidation reactions of carbon, silicon, manganese, and phosphorus.

• BOF Vessel Operation & Refining Protocol:

  • Charge Balance: The refractory-lined BOF vessel is charged with $\sim 20\,\%$ solid steel scrap followed by liquid pig iron ($80\,\%$).

  • Typical Hot Metal Chemistry: $4\,\%\text{ C}$, $0.2\text{--}0.8\,\%\text{ Si}$, $0.08\text{--}0.18\,\%\text{ P}$, $0.01\text{--}0.04\,\%\text{ S}$.

  • Oxygen Blow: A water-cooled lance is lowered into the upright vessel, blowing $99\,\%$ pure $O_2$ at supersonic speeds ($>\text{Mach }1$).

  • Thermal & Chemical Effects: Oxygen reacts with carbon to produce $CO$ and $CO_2$, raising the bath temperature to $\sim 1700\,^\circ\text{C}$. This melts the steel scrap, lowers carbon content, and oxidizes impurities.

  • Slag Formation: Burnt lime ($CaO$) or dolomite ($MgO$) fluxes are added, forming a gas-metal-slag emulsion with iron that rapidly absorbs oxidized impurities.

  • Blowing Duration: $\sim 20\,\text{minutes}$.

  • Blown Metal Chemistry: $0.3\text{--}0.6\,\%\text{ C}$, $0.05\text{--}0.1\,\%\text{ Mn}$, $0.01\text{--}0.03\,\%\text{ Si}$, $0.01\text{--}0.03\,\%\text{ S}$, $0.01\text{--}0.03\,\%\text{ P}$.

  • Tapping & Ladle Refining: The vessel is tilted to pour molten steel into a ladle where alloy additions are made. Argon ($Ar$) or Nitrogen ($N_2$) gas is bubbled through the bottom to homogenize temperature and alloy distribution. Final steel carbon content ranges from $0.1\text{ to }1.0\,\%$.

Philippine Associated Smelting and Refining Corporation (PASAR)

• Corporate Profile & Site Specifications:

  • Incorporated in 1976; located in the Leyte Industrial Development Estate (LIDE), Isabel, Leyte (530 km southeast of Manila).

  • PASAR is the only copper smelter and refinery in the Philippines and was the first of 11 major industrial projects under the Marcos administration.

  • Facility Dimensions: Covers an 80-hectare coastal site adjacent to the Philippine Phosphate Fertilizer Plant (Philphos).

  • Ownership: Majority owned by Glencore International since privatization in 1999.

  • Location Advantages: Proximity to Tongonan Geothermal Power Plant ($60\,km$ away), deep-water harbor at Dupon Bay, global copper concentrate suppliers, and international refined copper markets.

• Capacity Progression & Annual Production Outputs:

  • Original Capacity (1983): $138,000\,\text{MTPY}$.

  • October 1989 Expansion: Increased by $25\,\%$ to $172,500\,\text{MTPY}$ cathodes.

  • Conversion to ISA Process: Expanded plant capacity to $215,000\,\text{MTPY}$.

  • Current Product Output Capacities:

  • Electrolytic Copper Cathodes (PSR Isabel Brand, ISA Cathode, LME and SHFE registered, $99.99\,\%\text{ Cu}$): $220,000\,\text{DMt/year}$.

  • 3rd Party Refined Copper Anodes ($99.5\,\%\text{ Cu}$): $110,000\,\text{DMt/year}$.

  • Dore Metal ($18\text{--}21\,\%\text{ Au}$, $\sim 80\,\%\text{ Ag}$): $125\,\text{Mt/year}$.

  • Sulfuric Acid ($98\,\%\text{ H}_2\text{SO}_4$): $1,200\,\text{Mt/year}$.

  • Selenium Powder ($99.5\,\%\text{ Se}$): $105\,\text{Mt/year}$.

  • Copper Telluride ($15\text{--}21\,\%\text{ Te}$): $80\,\text{Mt/year}$.

  • Iron Concentrate ($\sim 42\,\%\text{ Fe}$): $850,000\,\text{Mt/year}$.

  • Gypsum ($CaSO_4$): $10,000\,\text{Mt/year}$.

• Raw Concentrate Sourcing:

  • Local and international mines supply copper concentrate: Grasberg (Indonesia), Batu Hijao (Indonesia), Philex (Philippines), Escondida (Chile), Ok Tedi (Papua New Guinea), Chelopech, Andina (Chile), Osbourne (Australia), Isa (Australia), Eloise (Australia), Highland Valley (Canada), Selwyn (Canada).

• Smelting & Refining Process Flow:

  • Port Handling & Unloading: Luffing crane unloads concentrate from vessels into a hopper connected to a conveyor belt system leading to the Concentrate Storage and Blending House (CSBH). Increment sampling is performed at conveyor belt #5 by MLPQD personnel.

  • Storage & Blending (CSBH): Girder-tripper-scraper systems stack wet concentrates into separate yards by brand name. Payloaders transfer concentrates to hoppers feeding a dynamic weigher, magnetic separator (for tramp iron removal), and a $2\text{"} \times 2\text{"}$ vibrating screen.

  • Flash Dryer: Reduces concentrate moisture from $10\,\%\text{ H}_2\text{O}$ down to $0.3\text{--}0.5\,\%\text{ H}_2\text{O}$ using heat ($700\,^\circ\text{C}$) supplied by an auxiliary heavy oil combustion furnace and anode furnace off-gas. Dried ore passes through a cage mill to reduce particle size to $\sim 20\text{-Mesh}$, through a dust chamber at $60\,^\circ\text{C}$, and into cyclones on the 9th floor.

  • Flash Smelting Furnace with Electrodes (FSFE):

  • Smelts dried concentrate with $50\,\%$ oxygen-enriched air into two immiscible liquid layers: copper matte ($62\text{--}65\,\%\text{ Cu}$) and slag ($1\,\%\text{ Cu}$).

  • Main Chemical Reactions:       $2CuFeS_2 + 4O_2 \rightarrow Cu_2S + 2FeO + 3SO_2$       $FeS_2 + \frac{5}{2}O_2 \rightarrow FeO + 2SO_2$       $FeS + \frac{3}{2}O_2 \rightarrow FeO + SO_2$       $2FeO + SiO_2 \rightarrow 2FeO \cdot SiO_2$       $3FeO + \frac{1}{2}O_2 \rightarrow Fe_3O_4$       $PbS + \frac{3}{2}O_2 \rightarrow PbO + SO_2$       $ZnS + \frac{3}{2}O_2 \rightarrow ZnO + SO_2$

  • Electrodes: Three delta-connected carbon electrodes melt and maintain slag fluidity at $1250\,^\circ\text{C}$; electrode length is replenished manually with Soderberg Paste sacks.

  • Tapping: Matte is tapped into ladles and carried by overhead crane to the Converter Furnace. Slag is tapped and granulated via seawater spray.

  • Converter Furnace (CF):

  • Uses 4 vessels (2 operating, 1 hot standby, 1 under maintenance). Enriched oxygen is blown through tuyeres.

  • Slag Blow: FeS is oxidized, producing White Metal ($72\,\%\text{ Cu}$) and converter slag.

  • Copper Blow: $Cu_2S$ is oxidized, producing Blister Copper ($98.5\,\%\text{ Cu}$).

  • Anode Furnace (AF) & Casting:

  • Refines Blister Copper from $98.5\,\%$ to $99.5\,\%\text{ Cu}$. Three steps: Skimming (slag removal), Blowing (air injection to remove sulfur), and Poling (LPG injection to reduce dissolved oxygen).

  • Molten copper is cast on the Anode Casting Wheel into refined copper anodes.

  • Slag Flotation Plant (SFP):

  • Treats FSF slag (cooled 24 hours) and CF slag (cooled 60 hours) in a 3:1 FSF:CF ratio.

  • Process: Crushing (Blake jaw crusher), grinding (SAG mill and Ball mill), classification (cyclones), flotation (rougher, scavenger, cleaner columns), and dewatering (thickeners and ceramic filters).

  • Products: Slag concentrate ($25\text{--}35\,\%\text{ Cu}$, recycled to CSBH) and final iron tailings ($0.25\text{--}0.35\,\%\text{ Cu}$).

  • Refinery (ISA Process Electrorefining):

  • Utilizes reusable stainless steel permanent cathode plates (ISA plates / mother blanks), eliminating starter sheets.

  • Anodes are set up using an Anode Spacing and Reforming Machine and placed into commercial cells alongside mother blanks.

  • Electrolysis: Copper dissolves from the anode ($99.5\,\%\text{ Cu}$) and deposits on the stainless steel cathode plate as $99.99\,\%\text{ Cu}$. Normal cell current is $400\text{--}800\,\text{A}$ (short circuit >$800\,\text{A}$).

  • Cathodes are removed via overhead crane, stripped using a Cathode Stripping Machine, weighed, and bundled for shipment. Spent anodes are washed in a Scrap Anode Washing Machine and recycled to the CF.

  • By-Products Plant (BPP) & Dore Plant:

  • BPP purifies electrolyte via electrowinning (depositing excess $Cu$, $Bi$, $Sn$, $As$ onto spent anodes) and collects anode slimes.

  • Dore Plant treats de-copperized slimes through roasters and furnaces to produce Dore Metal ($18\text{--}21\,\%\text{ Au}$, $\sim 80\,\%\text{ Ag}$).

  • Selenium Section: Uses a Se roaster, TROF furnace, filter press, and rotary dryer to produce $99.5\,\%$ pure Selenium Powder ($<200\text{-Mesh}$).

• Auxiliary Support Operations:

  • Acid Plant: Converts $SO_2$ off-gases from the FSFE and CF into $98\,\%$ commercial sulfuric acid ($H_2SO_4$).

  • Waste Acid Neutralization Plant (WANP): Neutralizes weak acid bleed to produce environmentally safe effluent discharge, gypsum cake, and heavy metal waste cakes.

  • Power Plant: Operates 3 x 1 MW backup diesel generators (saving up to 32-36 MW/day) and produces demineralized water for waste heat boiler cooling.

  • Oxygen Plant: Employs Cryogenic (Kobe, Linde) and Non-Cryogenic (PSA, Molecular Sieves) separation plants producing $99\,\%$ pure oxygen.

  • Quality Control (MLPQD): Conducts sampling, chemical wet analysis, and fire assaying.

• PASAR Personnel Breakdown:

  • Smelter Personnel Total [267]: 1 Assistant Vice-President (AVP), 5 Senior Managers (SM), 24 Area Managers (AM), 50 Senior Operators (SO), 187 Operators (O).

  • Refinery Personnel Total [165]: 1 AVP, 5 SM, 15 AM, 20 Senior Operators/Craftsmen (SO/C), 124 Operators/Craftsmen (O/C).

  • Auxiliary Personnel Total [81]: 1 AVP, 2 Department Heads (DH), 15 AM, 15 Senior Operators/Master Craftsmen/Leadmen (SO/MC/L), 48 Field Operators/Craftsmen/Operators (FO/C/O).

  • MLPQD Personnel Total [65]: 1 AVP, 1 SM, 11 AM, 27 Analysts/Senior Techs/Inspectors (A/ST/I), 23 Lab Techs (LT), 2 Sec/M.

Fundamentals of Pyrometallurgy and Material Balances

• Extractive Metallurgy Categories:

  • Hydrometallurgy: Selective chemical reaction of valuable metals using aqueous reagents.

  • Electrometallurgy: Electrical energy / electrolysis used to selectively deposit metals.

  • Pyrometallurgy: High-temperature thermal processing using dry reagents.

• Unit Operations vs. Unit Processes:

  • Unit Operations: Physical separation techniques involving no chemical reactions and no change in state of aggregation (e.g., comminution, screening, classification, solid-liquid separation, flotation, magnetic separation).

  • Unit Processes: High-temperature chemical processes involving chemical reactions and phase/state changes (e.g., calcination, roasting, gaseous reduction, sintering, smelting, converting, liquid refining, casting).

• Core Pyrometallurgical Processes:

  • Calcination: Heating carbonate ores below their melting point in the absence of air to cause thermal decomposition into oxides:     $CaCO_3 \rightarrow CaO + CO_2$     $MnCO_3 \rightarrow MnO + CO_2$

  • Roasting: Heating sulfide ores in excess air below their melting point to convert them to metal oxides or sulfates:

  • Oxidizing Roast: $2Cu_2S + 3O_2 \rightarrow 2Cu_2O + 2SO_2$

  • Sulfatizing Roast: $CuO + SO_3 \rightarrow CuSO_4$

  • Reduction Roast: $NiO + CO \rightarrow Ni + CO_2$

  • Smelting: "Separation by melting" - melting feed charges to form two immiscible liquid phases (liquid metal/matte and liquid slag).

  • Converting: Oxidizing liquid matte by blowing oxygen or air to selectively remove sulfur and iron.

  • Retorting: Dry distillation process that volatilizes a metal from a liquid melt and condenses it elsewhere.

• Phases in Metallurgical Systems:

  • Matte: Molten solution of sulfides formed during smelting ($Cu$, $Ni$, $Pb$).

  • Speiss: Unwanted molten solution of arsenides ($Fe$, $Co$, $Ni$, $Cu$) settling between matte and slag.

  • Dross: Solid crust of oxidized impurities floating on low-melting metals/alloys.

  • Slag: Molten solution of oxides floating on top of liquid metal or matte. Functions as an impurity collector, additive solvent, protective cover against atmospheric oxidation, and electric resistance heating element in electric furnaces.

• Gas Laws & Fundamental Stoichiometric Principles:

  • Law of Conservation of Elements: Matter is neither created nor destroyed. Element mass inputs must balance element mass outputs under steady-state conditions.

  • Principle of Combining Weights: Relative weights of reacting compounds are fixed multiples of atomic weights.

  • Law of Combining Volumes: Volumes of reacting gases measured at identical temperature and pressure are simple whole-number ratios.

  • Boyle's Law: At constant temperature, $V \propto \frac{1}{P}$.

  • Charles's Law: At constant pressure, $V \propto T$.

  • Gay-Lussac's Law: Thermal expansion coefficient of ideal gases $\alpha = \frac{1}{273.15}$. Absolute Zero $= -273.15\,^\circ\text{C} = 0\,\text{K}$.

  • Ideal Gas Law: $P V = n R T$.

  • Molar Gas Volumes at STP ($0\,^\circ\text{C} / 273\,\text{K}$, $1\,\text{atm}$):

  • $1\,\text{g-mol} = 22.4\,\text{liters}$

  • $1\,\text{kg-mol} = 22.4\,\text{m}^3$

  • $1\,\text{lb-mol} = 359\,\text{ft}^3$

  • Gas Mixture Rule: Volume $\%$ $=$ Mol $\%$. Partial Pressure $=$ Total Pressure $\times$ Mol Fraction.

  • Stoichiometric Air Composition: $21\,\%\text{ O}_2 : 79\,\%\text{ N}_2$ by volume/moles.

• General Procedure for Solving Metallurgical Problems:

  1. Draw a simple system sketch with labeled feed and product streams.

  2. Enter known quantitative and chemical analysis data.

  3. Note process assumptions (e.g., metal distribution percentages among phase layers).

  4. Choose a convenient calculation basis (e.g., $1\,\text{hour}$, $24\,\text{hours}$, $100\,\text{kg}$, $60\,\text{Mt}$).

  5. Write balanced stoichiometric chemical equations.

  6. Write independent element mass balance equations.

  7. Solve equations sequentially for unknowns.

  8. Construct a complete Metallurgical Balance Table (Inputs vs. Outputs).

  9. Perform independent mathematical verification.

• Worked Example 1: Copper Converter Material Balance

  • Problem Statement: A converter receives $60\,\text{Mt}$ matte analyzing $54\,\%\text{ FeS}$. $FeS$ is completely oxidized to $FeO$ by blowing dry air, forming $SO_2$ gas. Slag contains $65\,\%\text{ FeS}$-derived $FeO$.

  • Calculations:

  • Weight of $FeS$ in matte $= 60\,\text{Mt} \times 0.54 = 32.4\,\text{Mt} = 32,400\,\text{kg}$.

  • Moles of $FeS$ ($MW = 88\,\text{kg/kg-mol}$) $= \frac{32,400}{88} = 368.2\,\text{kg-mol}$.

  • Reaction: $FeS + \frac{3}{2}O_2 \rightarrow FeO + SO_2$

  • Moles of $O_2$ required $= 368.2 \times 1.5 = 552.3\,\text{kg-mol}$.

  • Volume of $O_2$ at STP = 552.3\,\text{kg-mol} \times 22.4\,\text{m}^3\text{/kg-mol} = 12,371.52\,\text{m}^3$.\n - Total dry air volume = \frac{12,371.52}{0.21} = 58,912\,\text{m}^3$.

  • Moles of $SO_2$ formed $= 368.2\,\text{kg-mol}$; Volume of $SO_2$ = 368.2 \times 22.4 = 8,248\,\text{m}^3$.\n - Moles of FeO$formed$= 368.2\,\text{kg-mol}.\n - Weight of FeO$($MW = 72\,\text{kg/kg-mol}$)$= 368.2 \times 72 = 26,510\,\text{kg}.\n - Weight of slag = \frac{26,510\,\text{kg}}{0.65} \times \frac{1\,\text{Mt}}{1000\,\text{kg}} = 40.79\,\text{Mt}$.

  • Metallurgical Balance Table (Basis: $60\,\text{Mt}$ Matte):

  • Inputs: $FeS = 368.2\,\text{kg-mol}$ ($32,400\,\text{kg}$); $O_2 = 552.3\,\text{kg-mol}$.

  • Outputs: $FeO = 368.2\,\text{kg-mol}$ ($26,510\,\text{kg}$); $SO_2 = 368.2\,\text{kg-mol}$.

Thermochemistry, Heat Balances, and Heat Transfer

• Metallurgical Heat Balance Principles:

  • Derived from the First Law of Thermodynamics ($\text{Energy Input} = \text{Energy Output}$).

  • Input Energy Terms: Sensible heat of incoming feed materials, exothermic heats of reaction, external heat supplied (combustion or electrical).

  • Output Energy Terms: Sensible heat of outgoing products (metal, slag, flue gas), endothermic heats of reaction, heat required to bring feed materials to reference temperature, furnace wall radiation/conduction heat losses.

• Enthalpy & Kirchoff's Law:

  • Heat capacity integral for temperature change from $298\,\text{K}$ to $T_f$:     $\Delta H_{T_f} = \Delta H_{298}^\circ + \int_{298}^{T_f} \Delta C_p\,dT$

  • Where $\Delta C_p = \sum C_{p,\text{products}} - \sum C_{p,\text{reactants}}$.

• Worked Example 4: Heat Balance of Limestone Calcination

  • Reaction: $CaCO_3 \rightarrow CaO + CO_2$

  • Basis: $1\,\text{g-mol}$ ($100\,\text{g}$) $CaCO_3$.

  • Thermochemical Data:

  • $\Delta H_{f,\text{CaCO}_3}^\circ = -288.4\,\text{kcal/mol}$; $\Delta H_{f,\text{CaO}}^\circ = -151.6\,\text{kcal/mol}$; $\Delta H_{f,\text{CO}_2}^\circ = -94.05\,\text{kcal/mol}$.

  • Heat of reaction at $298\,\text{K}$ ($25\,^\circ\text{C}$): $\Delta H_{rxn,298}^\circ = +42,750\,\text{cal}$ (endothermic).

  • Integrated sensible heats from $298\,\text{K}\text{ to }1173\,\text{K}$ ($900\,^\circ\text{C}$):

    • $\Delta H_{\text{CaO}} = 10,515.80\,\text{cal}$

    • $\Delta H_{\text{CO}_2} = 10,110.69\,\text{cal}$

    • $\Delta H_{\text{CaCO}_3} = 23,677.79\,\text{cal}$

  • Heat Balance at Reference Temperature $T_{ref} = 25\,^\circ\text{C}$ ($298\,\text{K}$):

  • Input Sensible Heat: $CaCO_3 = 0.00\,\text{cal}$.

  • Output Sensible Heat: $CaO = 10,515.80\,\text{cal}$; $CO_2 = 10,110.69\,\text{cal}$.

  • Output Reaction Enthalpy ($\Delta H_{rxn,298}$): $42,750.00\,\text{cal}$.

  • Total External Heat Required $= 10,515.80 + 10,110.69 + 42,750.00 = 63,379.49\,\text{cal}$.

  • Heat Balance at Reference Temperature $T_{ref} = 900\,^\circ\text{C}$ ($1173\,\text{K}$):

  • Heat absorbed by $CaCO_3$ to reach $1173\,\text{K} = 23,677.79\,\text{cal}$.

  • Heat of reaction at $1173\,\text{K}$ ($\Delta H_{rxn,1173}$) $= 39,698.41\,\text{cal}$.

  • Total External Heat Required $= 23,677.79 + 39,698.41 = 63,379.49\,\text{cal}$.

• Heat Utilization & High Temperature Energy Concepts:

  • Critical Process Temperature (CPT): The minimum temperature required to execute chemical reactions effectively and achieve fluid slag flow ($1500\,^\circ\text{C}$ for iron blast furnace slags).

  • Adiabatic Flame Temperature (AFT): The maximum theoretical temperature attained by combustion products assuming complete reaction under zero heat loss conditions.

  • Actual Flame Temperature: Typically $48\,\%\text{ to }75\,\%$ of AFT due to non-adiabatic radiation loss, incomplete combustion, and atmospheric moisture.

  • Gross Available Heat: Total combustion heat minus sensible heat carried away by flue gas products at CPT.

  • Net Available Heat: Gross available heat minus furnace wall heat losses.

  • Smelting Power: Maximum furnace throughput capacity per unit time.

• Heat Exchanger Types:

  • Recuperators: Continuous-flow heat exchangers where hot flue gas and cold incoming air flow concurrently or counter-currently through channels separated by conductive walls.

  • Regenerators: Batch/cyclic heat exchangers containing refractory checkerwork matrices that alternately absorb thermal energy from hot flue gases and release it to incoming cold air.

• Mechanisms of Heat Transfer:

  • Fourier's Law of Heat Conduction:     $q_x = -k \frac{dT}{dx} \quad \text{and} \quad Q_x = -k A \frac{dT}{dx}$     Where $q_x$ is heat flux, $Q_x$ is overall heat flow rate, $k$ is thermal conductivity, and $\frac{dT}{dx}$ is the temperature gradient.

  • Composite Flat Walls / Slabs:     $Q_x = \frac{A (T_i - T_o)}{\frac{1}{h_i} + \sum \frac{L_n}{k_n} + \frac{1}{h_o}}$

  • Composite Cylinders:     $Q_x = \frac{2 \pi L (T_i - T_o)}{\frac{1}{r_i h_i} + \sum \frac{\ln(r_{n+1}/r_n)}{k_n} + \frac{1}{r_o h_o}}$

• Worked Examples in Heat Transfer:

  • Example 6 (Lead Slab): Slab of lead ($k = 35\,\text{W/m}\cdot\text{K}$, thickness $L = 0.03\,\text{m}$, area $A = 0.4\,\text{m}^2$) with front face at $110\,^\circ\text{C}$ and back face at $50\,^\circ\text{C}$.

  • Heat Flux: q = k \frac{\Delta T}{L} = 35 \times \frac{110 - 50}{0.03} = 70,000\,\text{W/m}^2$.\n - Heat Transfer Rate: Q = q \times A = 70,000 \times 0.4 = 28,000\,\text{W}.\n - **Example 7 (Copper Composite Wall):** 3\,\text{mm}$copper plate ($k_2 = 372\,\text{W/m}\cdot\text{K}$) clad on both sides by$2\,\text{mm}$stainless steel layers ($k_1 = k_3 = 17\,\text{W/m}\cdot\text{K}$) between$400\,^\circ\text{C}$and$100\,^\circ\text{C}.\n\n# Industrial Furnaces and Refractory Systems\n\n- **Furnace Classification Categories:**\n - **Class I - Crucible Furnaces:** Fuel-fired or induction heated. Charge is isolated inside a crucible.\n - **Class II - Hearth Furnaces:** Flame or electric arc heats the shallow bath directly or by roof radiation (e.g., Reverberatory, Open Hearth, Electric Arc Furnace).\n - **Class III - Shaft Furnaces:** Vertical stack design for continuous processing where gravity-fed charge descends against rising hot gas (e.g., Iron Blast Furnace, Cupola Furnace).\n - **Special Reactors:** Converters (gas blown through liquid melt), Retorts (dry distillation/volatilization), Rotary Kilns (inclined rotating cylinders for drying, roasting, direct reduction).\n\n- **Melting Point Classification of Metals:**\n - **Low Melting Point (<600\,^\circ\text{C}$):** Mercury ($Hg$), Potassium ($K$), Cadmium ($Cd$), Sodium ($Na$), Zinc ($Zn$), Lithium ($Li$), Bismuth ($Bi$), Lead ($Pb$), Tin ($Sn).\n - **Medium Melting Point (600\text{--}1100\,^\circ\text{C}$):** Arsenic ($As$), Magnesium ($Mg$), Antimony ($Sb$), Calcium ($Ca$), Aluminum ($Al$), Silver ($Ag$), Copper ($Cu$), Gold ($Au).\n - **High Melting Point (1100\text{--}1600\,^\circ\text{C}$):** Manganese ($Mn$), Silicon ($Si$), Beryllium ($Be$), Chromium ($Cr$), Nickel ($Ni$), Iron ($Fe$), Cobalt ($Co).\n - **Very High Melting Point (>1600\,^\circ\text{C}$):** Titanium ($Ti$), Vanadium ($V$), Platinum ($Pt$), Zirconium ($Zr$), Tantalum ($Ta$), Molybdenum ($Mo$), Tungsten ($W).\n\n- **Slag Chemistry & Oxide Acid-Base Hierarchy:**\n - Oxides behave along an acidity/basicity spectrum ranging from oxygen acceptors (acidic) to oxygen donors (basic):\n - **Acidic Oxides (Oxygen Acceptors):** B_2O_3$,$SiO_2$,$P_2O_5.\n - **Amphoteric Oxides:** Al_2O_3$,$TiO_2$,$BeO.\n - **Basic Oxides (Oxygen Donors):** FeO$,$MgO$,$MnO$,$Li_2O$,$CaO$,$Na_2O.\n - **Refractory & Slag Selection Rules:**\n - If pig iron is high in phosphorus, an oxidizing blow produces acidic P_2O_5$. To neutralize, a basic slag ($CaO$,$MgO$) and basic refractory lining ($MgO) are used.\n - If pig iron is high in sulfur, desulfurization generates basic CaS/CaSO_4$. To balance, an acidic slag ($SiO_2$) and acidic refractory ($SiO_2) are used.\n\n# Hydrometallurgical Extraction: The Sherritt Gordon Process\n\n- **Background & Feedstock Characteristics:**\n - Developed by Sherritt Gordon Mines Ltd. in Manitoba, Canada, based on the Forward Process created by Dr. Frank Arthur Forward.\n - It represents the first successful commercial application of pressure hydrometallurgy to a complex sulfide feed.\n - Feedstock: Pentlandite (NiS \cdot FeS$) concentrates or flash-smelted matte containing$\sim 29\,\%\text{ Cu}$,$12\,\%\text{ Ni}$,$0.4\,\%\text{ Co}$, and$30\,\%\text{ S}.\n\n- **Complete 16-Step Hydrometallurgical Flowsheet:**\n 1. **Pre-treatment of Feed:** Concentrates/mattes are roasted or flash-smelted to prepare feed material.\n 2. **Ammoniacal Pressure Leaching:** Matte/sulfides are pressure-leached at 8\,\text{atm}$and$105\,^\circ\text{C}$in aqueous ammonia ($NH_3) with air injection, dissolving nickel, cobalt, and copper as soluble amine complexes.\n 3. **Removal of Barren Solids:** Unreacted iron hydroxide (Fe(OH)_3) and gangue solids precipitate and are filtered off to the dump.\n 4. **Precipitation of Copper:** Ammonia is boiled off from solution, causing thiosulfate and polythionate ions to react with copper, precipitating copper sulfide (CuS), which is filtered and sent to a copper smelter.\n 5. **Final Copper Stripping:** Hydrogen sulfide (H_2S) is added in an autoclave to precipitate residual nickel and copper sulfides, which are recycled to Step 2.\n 6. **Oxyhydrolysis:** Solution is treated in an autoclave at 50\,\text{atm}$and$200\,^\circ\text{C} with air injection to oxidize thionates to sulfate, preventing fertilizer contamination:\n     S_2O_3^{2-} + 2O_2 + 2OH^- \rightarrow 2SO_4^{2-} + H_2O\n 7. **Nickel Reduction:** Hydrogen gas (H_2$) is injected at$15\,\text{atm}$and$175\,^\circ\text{C} into the nickel amine solution seeded with nickel powder:\n     Ni(NH_3)_2^{2+} + H_2 \rightarrow Ni^0 + 2NH_4^+\n     Precipitates metallic nickel powder (99\,\%\text{ Ni}).\n 8. **Mixed Sulfide Precipitation:** H_2S$is added at$7\,\text{atm}$and$120\,^\circ\text{C}$to precipitate remaining nickel and cobalt as mixed sulfides ($NiS/CoS).\n 9. **Excess Ammonia Removal:** The barren solution is evaporated and crystallized to yield ammonium sulfate, (NH_4)_2SO_4, sold as fertilizer.\n 10. **Acidic Pressure Leaching of Mixed Sulfides:** Mixed sulfides are re-leached with H_2SO_4$and air at$7\,\text{atm}$and$120\,^\circ\text{C}.\n 11. **Final Iron Removal:** Ammonia (NH_3$) is added to precipitate trace iron as Jarosite,$KFe_3(OH)_6(SO_4)_2, sent to the dump.\n 12. **Cobalt Conversion:** Air and NH_3$are injected to oxidize divalent cobalt ($Co^{2+}$) to trivalent cobaltic amine complex,$Co(NH_3)_5^{3+}, while nickel remains divalent.\n 13. **Nickel Removal:** Sulfuric acid (H_2SO_4$) is added to acidify solution and selectively precipitate nickel as nickel(II) sulfate-ammonium sulfate hexahydrate,$(NiSO_4) \cdot ((NH_4)_2SO_4) \cdot 6H_2O, recycled to Step 2.\n 14. **Cobalt Reduction:** Additional H_2SO_4 and cobalt seed powder are added to the de-nickeled solution.\n 15. **Cobalt Precipitation:** H_2$gas is injected to precipitate cobalt metal powder ($99.6\,\%\text{ Co}).\n 16. **Barren Solution Treatment:** Final liquid residue is evaporated to crystallize additional (NH_4)_2SO_4$$ fertilizer.