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This is the complete lecture note for MME413 Chemical Metallurgy. You can read it online below, open it in the full viewer, or download the PDF for offline study. It pairs with the course's video lectures, so you can read and watch together.
Course code: MME 413 Course title: Chemical Metallurgy Course credit load: 2 Units Series 1: Chemical Principles and Thermodynamics of Metallurgical Processes • Part 1.1: Chemical Principles in Metallurgy o Sub Part 1.1.1: The Scope of Chemical Metallurgy o Sub Part 1.1.2: Stoichiometry and Material Balances o Sub Part 1.1.3: Gases and Gas Mixtures • Part 1.2: Thermodynamic Foundations o Sub Part 1.2.1: The First Law, Enthalpy and Heat Capacity o Sub Part 1.2.2: The Second Law, Entropy and Gibbs Free Energy o Sub Part 1.2.3: Equilibrium and the Equilibrium Constant • Part 1.3: Solutions, Activity and Phase Equilibria o Sub Part 1.3.1: Ideal and Real Solutions o Sub Part 1.3.2: Free Energy of Mixing and Regular Solutions o Sub Part 1.3.3: Phase Equilibria in Metallurgical Systems • Part 1.4: Ellingham Diagrams and Reaction Kinetics o Sub Part 1.4.1: Ellingham Diagrams o Sub Part 1.4.2: Using Ellingham Diagrams to Reduce Oxides o Sub Part 1.4.3: Rates of Chemical Reactions Introduction Inside a smelting furnace no one can watch what is happening, yet every reaction obeys rules that can be written down and used to predict the result. Whether an ore will yield metal, how much reductant it needs and how hot the furnace must be are questions that chemistry and
thermodynamics can answer before a furnace is ever lit. This Series sets out those principles and the quantitative tools that turn them into predictions. The aim of this Series is to equip you to explain the fundamental chemical principles of metallurgical reactions, apply thermodynamics quantitatively, and use Ellingham diagrams and the ideas of reaction rate to analyse metallurgical processes. We shall commence with chemical principles in metallurgy, including material balances and gases. Next, we will explore thermodynamic foundations, from enthalpy to the equilibrium constant. Afterwards, we will turn to solutions, activity and phase equilibria. We will conclude with Ellingham diagrams and reaction kinetics. Series Learning Outcomes Upon completing this Series, you should be able to: • SLO 1.1: describe the scope of chemical metallurgy and the main routes for extracting and refining metals, • SLO 1.2: perform stoichiometric, material balance and gas mixture calculations for metallurgical systems, • SLO 1.3: apply the first law, enthalpy and Hess's law to metallurgical reactions, • SLO 1.4: apply the second law and Gibbs free energy to predict spontaneity and calculate equilibrium constants, • SLO 1.5: apply Raoult's law, Henry's law and the concept of activity to solutions, • SLO 1.6: explain the free energy of mixing and the distribution of solutes between metal and slag, • SLO 1.7: construct and interpret Ellingham diagrams to predict the reduction of oxides, • SLO 1.8: explain the rates of chemical reactions and the difference between thermodynamic feasibility and kinetic control. 1.1 Chemical Principles in Metallurgy 1.1.1 The Scope of Chemical Metallurgy Chemical metallurgy is the application of chemistry, thermodynamics and transport principles to the extraction, refining and processing of metals. Most metals occur as oxides, sulphides or
carbonates in ores, and the task is to convert them into pure metal at acceptable cost. The routes are grouped as pyrometallurgy, which uses high temperature, hydrometallurgy, which uses aqueous solutions, and electrometallurgy, which uses electric current. This course concentrates on the pyrometallurgical processes. A typical route begins with mining and mineral processing to make a concentrate. The concentrate may be roasted, agglomerated and smelted to give a metal or a matte, converted to raise its purity, and refined to the final grade, before it is melted and cast. Each stage rests on the same three foundations: the thermodynamics that decides which reactions can occur, the kinetics and transport that decide how fast they occur, and the balances of mass and energy that decide the size of the furnace. Worked example: Copper is often extracted from a sulphide concentrate by roasting, smelting to a matte, converting and fire refining, all of which are high-temperature steps, whereas leaching copper oxide ore with sulphuric acid is hydrometallurgy. Application: Identifying the route as pyro-, hydro- or electrometallurgy shows which principles apply and what equipment is needed. Fill in the blank: The extraction of metals using high temperature is called __________. 1.1.2 Stoichiometry and Material Balances Stoichiometry is the quantitative relationship between the amounts of substances in a balanced chemical equation. The amount of a substance is expressed in moles, and one mole of an element has a mass equal to its atomic mass in grams. The compositions of ores, metals and slags are usually given in weight per cent, and they are converted to moles by dividing by the atomic or molecular mass. A material balance states that the mass of everything entering a process equals the mass of everything leaving it, plus any accumulation. Balances are written for each element, since elements are conserved in chemical reactions, and they show the amounts of reagents needed and of products formed. A basis, such as 1 tonne of ore, is chosen, and the balance is solved for the unknowns, which include the amounts of slag and gas. Worked example: For Fe2O3 + 3CO = 2Fe + 3CO2, making 1 tonne of iron needs 17 900 moles of iron, which needs 8950 moles of Fe2O3, or 1.43 tonnes, and 26 900 moles of CO, which is about 600 cubic metres at standard conditions. Application: Stoichiometry and material balances give the quantities of ore, reductant and flux that are needed and the amounts of waste that are produced. Fill in the blank: A statement that the mass entering a process equals the mass leaving it, plus accumulation, is a __________ balance. 1.1.3 Gases and Gas Mixtures
Gases are important in metallurgy as reductants, oxidants and products. An ideal gas obeys PV = nRT, where R is 8.314 joules per mole per kelvin, and this is a good approximation for furnace gases at high temperature and near atmospheric pressure. One mole occupies 22.4 litres at 273 kelvin and 1 atmosphere, and the volume rises in proportion to the absolute temperature, so a mole of gas at furnace temperature occupies several times more space than at room temperature. In a gas mixture, Dalton's law states that the total pressure is the sum of the partial pressures, and the partial pressure of each gas is its mole fraction multiplied by the total pressure, pi = XiP. The partial pressures of gases such as CO, CO2, O2 and SO2 determine the direction of reactions, so the furnace atmosphere is described by its composition. Gas volumes must always be stated together with the temperature and pressure. Worked example: A furnace gas of 30 per cent CO, 10 per cent CO2 and 60 per cent nitrogen at 1 atmosphere has pCO = 0.30 atmosphere and pCO2 = 0.10 atmosphere, and one mole of it at 1200 kelvin occupies about 98.5 litres. Application: Gas composition and volume calculations are needed to design furnaces, blowers and gas-cleaning systems. Fill in the blank: In a gas mixture, the partial pressure of each gas equals its mole fraction multiplied by the __________ pressure. Figure 1.1: General flowsheet of the pyrometallurgical extraction of a metal. Pilot questions 1.1 1. Define chemical metallurgy. (Linked to SLO 1.1)
2. Name the three groups of extraction routes. (Linked to SLO 1.1) 3. List the main stages of a typical pyrometallurgical route. (Linked to SLO 1.1) 4. What does a material balance state? (Linked to SLO 1.2) 5. State Dalton's law of partial pressures. (Linked to SLO 1.2) 1.2 Thermodynamic Foundations 1.2.1 The First Law, Enthalpy and Heat Capacity The first law of thermodynamics states that energy is conserved, so that the change in internal energy equals the heat absorbed minus the work done. At constant pressure, the heat absorbed is the change in enthalpy, ΔH, which is negative for exothermic reactions that release heat and positive for endothermic reactions that absorb it. The standard enthalpy of formation is the enthalpy change when one mole of a compound forms from its elements in their standard states at 298 kelvin. Hess's law states that the enthalpy change of a reaction is independent of the route, so the enthalpy of a reaction can be found by adding the enthalpies of other reactions. The effect of temperature is found from the heat capacities, since ΔH(T) = ΔH(298) + ∫ΔCp dT, integrated from 298 kelvin to T, with extra terms for the latent heats of any phase changes. Enthalpies give the heat that a furnace must supply or remove. Worked example: Since C + O2 giving CO2 has ΔH = -393.5 kJ, and CO + ½O2 giving CO2 has ΔH = -283.0 kJ, subtracting gives ΔH = -110.5 kJ for C + ½O2 giving CO. Application: Enthalpy calculations give the heat released or needed by reactions such as roasting and converting, which determines the fuel needs of a furnace. Fill in the blank: The enthalpy change of a reaction is independent of the route taken, which is __________ law. 1.2.2 The Second Law, Entropy and Gibbs Free Energy The second law of thermodynamics introduces
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