Chem Highlights of last lecture. This lecture. Australian Mining Sites. A/Prof Sébastien Perrier. Metallurgy: (Extracting metal from ore)

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1 Chem 111 A/Prof Sébastien Perrier Room: 351 Phone: Unless otherwise stated, all images in this file have been reproduced from: Blackman, Bottle, Schmid, Mocerino and Wille, Chemistry, 7 (John Wiley) ISBN: Slide 25-1 Prof Scott Kable Room: 311 Phone: s.kable@chem.usyd.edu.au A/Prof Adam Bridgeman Room: 222 Phone: a.bridgeman@chem.usyd.edu.au Slide 25-2 Highlights of last lecture This lecture Eq m constants involving liquids and solids Concentration of liq. and solids not included Le Chatelier s Principle adding/removing reagent inc. / dec. pressure inc. / dec. volume adding inert gas change of temperature effect of catalyst Slide 25-3 Extraction of metals from ores General principles, then The Indispenable three : Copper Steel Aluminium (in a later section) We will use our knowledge of thermochemistry and equilibrium to investigate how these chemicals/materials are produced. Good refs: Blackman, et al., Chemistry, 1 st ed., pp Silberberg, Chemistry, 3 rd ed., pp McMurray and Fay, Chemistry, 3 rd ed., pp Slide 25-4 Metallurgy: (Extracting metal from ore) Australian Mining Sites Commercially important ores: Lead, Zinc Aluminium Titanium Iron Gove Weipa McArthur R. Western Seaboard Hammersley Darling Range Mt Isa Broken Hill Eastern Seaboard Slide 25-5 Slide

2 Chemical composition of ores Metallurgy: (Extracting metal from ore) More ionic More covalent Ref: McMurray and Fay, p. 912 One of Australia s most important commodities How do you extract metals from ores? Mining Pre-treatment Chemical processing: mineral to compound Chemical processing: compound to metal Refining Alloying s-block Group 3B p,d-block Noble metals Slide 25-7 also Blackman Fig Slide 25-8 Pretreatment Froth Flotation Several methods of pretreating the ore to obtain the mineral: Flotation, Cyclone, Magnetism, Leaching Lighter particles (gangue) Pulverised ore Hydrophobic particles are captured in the froth layer Upward moving air stream Heavier particles Ref: Silb., p.964 (mineral) Slide 25-9 Figure 13.4 Blackman Slide 25-1 Mineral to Compound The most common way to convert the mineral into a uniform chemical compound is to roast it in air, e.g. CaCO 3 (s) + heat CaO(s) + CO 2 (g) or 2ZnS(s) + 3O 2 (g) + heat 2ZnO(s) + 2SO 2 (g) A source of acid rain. Now sulfur oxides are scrubbed from smokestack, and recycled into sulfuric acid (see next lecture) o Compound to Metal There are two main ways to form the pure metal from its oxide, depending on how reactive the metal is: a) Reduction with carbon (smelting, known since Egyptian times); b) Reduction with hydrogen (when carbide formation is a problem; c) Reduction with more active metal (when hydride formation is a problem); and Electrochemical reduction (known for about 15 years) Ref: Chemical Storylines, p.282 Slide Slide

3 Reduction with carbon Consider the formation reactions: K p (3 K) (1) C(graphite) +.5O 2 (g) CO(g) + heat 4.7x1 23 (2) Zn(s) +.5 O 2 (g) ZnO(s) + more heat 2.3x1 54 (1)-(2) ZnO(s) + C(gr.) + heat Zn(s) + CO(g) 2.x1-31 Reduction with carbon Consider the formation reactions: K p (3 K) (1) C(graphite) +.5O 2 (g) CO(g) + heat 4.7x1 23 (2) Zn(s) +.5 O 2 (g) ZnO(s) + more heat 2.3x1 54 (1)-(2) ZnO(s) + C(gr.) + heat Zn(s) + CO(g) 2.x1-31 H =? positive S =? positive Favours reactants enormously! So, how will eq m vary with temperature? (think about how G changes ) Slide Temp (K) K p 3.4x x x x1 3 9.x1 4 Le Chatelier at work! Slide Reduction with carbon Ca - CaO Al - Al 2 O 3 Note ln scale 6 4 Zn(s) +.5 O 2 (g) ZnO(s) ZnO Zn 6 4 Notice order of elements C(graphite) +.5O 2 (g) CO(g) Slide Zn - ZnO C - CO Fe - FeO Ni - NiO Slide Compound to Metal Is there a chemical explanation for this trend? Metal Ca Electronegativity 1. Al 1.5 Zn 1.6 Fe 1.8 Ni 1.9 Most stable oxides Oxygen is very electronegative. Which elements most readily give up their electrons to form stable oxides? Slide Least active Most active Metal Au, Pt Cu, Ag, Hg, Ni, Co V, Cr, Mn, Fe, Ti, Sn Al, Li, Na, Mg Reduction Method None; found in nature as free metal Roast sulfide to oxide reduction using carbon, hydrogen, or more active metal electrolysis Slide

4 Example: Production of Copper Copper has been mined since ancient times, maybe 35 BC Copper deposits formed in magma pools and occur mostly as sulfides, CuS Near the surface, the minerals are altered by exposure to oxygen, into other minerals, e.g. cuprite (Cu 2 O), tenorite (CuO), malachite, Cu 2 (OH) 2 CO 3 Formation reaction for oxide: Cu(s) +.5 O 2 (g) CuO(s) + heat K p =4.3x1 22 ln(k) = 52.1 E.N. = 1.9 Look back at Ellingham plot and electronegativity table and predict how the ancients might have reduced CuO. Slide Cu-CuO Ca - CaO Al - Al 2 O 3 Zn - ZnO C - CO Fe - FeO Ni - NiO Slide 25- Chemical composition of ores Example: Production of Copper More ionic More covalent Ref: McMurray and Fay, p. 912 Surface deposits of copper oxides soon ran out. Larger deposits of sulfides were available. Sulfides converted to oxides by roasting. CuS(s) O 2 (g) CuO(s) + SO 2 (g) add heat to increase rate s-block Group 3B p,d-block Noble metals Slide Largest deposits of copper are chalcopyrite, which contain iron Chalcopyrite is ground, then froth flotation is used to separate mineral from gangue The sulfide is smelted directly to Cu metal Slide Example: Production of Copper Chalcopyrite + silica (SiO 2 ) Fuel Overall reaction: O 2 Waste gases, SO 2 Copper Slag (impure, 2% S) electrolytic refining 4 CuFeS 2 (s) O 2 (g) 4 Cu(s) + 2 FeO(l) + Fe 2 O 3 (s) + 8 SO 2 (g) Slide Iron/steel is the most widely used of all metals, with some 75 million tonnes per year produced worldwide. Iron has been smelted since ~3 BC In 1773, a cheap process to produce coke (carbon) from coal, and the advent of the blast furnace, led to large-scale iron production and the Industrial Revolution. Important iron minerals: Mineral type Oxide Carbonate Sulfide Mineral, formula Hematite, Fe 2 O 3 Magnetite, Fe 3 O 4 Ilmenite, FeTiO 3 Siderite, FeCO 3 Pyrite, FeS 2 Pyrrhotite, FeS Figure Blackman Slide

5 Ore, CaCO 3, C The overall reaction uses CO as reducing agent: Fe 2 O 3 (s) + 3CO(g) 2Fe(l) + 3CO 2 (g) But this is the overall reaction and hides a multitude of processes. The process of converting iron ore into iron and steel involves a series of reductions of the ore, and acid-base steps. Although these seem simple enough, the detailed chemistry is very complex, and perhaps not fully understood even now. Solids drop Hot gases rise 3Fe 2 O 3 + CO 2 Fe 3 O 4 + CO 2 Fe 3 O 4 + CO 3FeO + CO 2 CaCO 3 CaO + CO 2 C + CO 2 2 CO FeO + CO Fe + CO 2 Impure iron melts. Molten slag forms 2C + O 2 2 CO Temp ºC 7ºC 1ºC 15ºC ºC Hot air blast Slide Slag Molten iron Slag floats on iron, like Earth s crust Slide on core Slide The iron from the furnace is impure and called pig iron. It contains typically 3-4% carbon Iron is purified and converted to steel by the basic oxygen process. High pressure O 2 is blown over the molten iron. Impurities with very stable oxides form (e.g. C, Si, P, Mn, S) It is too hot for less stable oxides, inc. iron. CaO (lime) is added, which reacts with these oxides to form a variety of phosphates, silicates, etc, all termed slag, which again float on the surface of the molten steel. Now 1% C, and very low other impurities and ready to alloying, e.g. Cr. to make stainless steel. Ref, Silberberg, p.972 Slide Example questions CONCEPTS reduction of metal oxide use of Ellingham graph knowledge of the production of Cu, steel CALCULATIONS Equilibrium and thermochemistry calculations involving metallurgy. Slide