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6. Reduction of Ores Copy 2 METAL CYCLE CONVERTING STONE Ore INTO Smelting Corrosion METAL Metal Metal Artifatcs EXTRUCTIVE METALLURGY Production OXIDATION POTENTIAL OF SOME METALS STABILITY OF METAL EO (volts) OXIDES Au Au+3 + 3e- -1.50 Ag Ag+ + e- -0.80 OXIDE ΔG(kJ) +2 - Cu Cu + 2e -0.34 Au2O3 +163.2 Pb Pb+2 + 2e- 0.13 Ag2O -10.8 Sn Sn+2 + 2e- 0.14 Cu O -146.4 Fe Fe+2 + 2e- 0.44 2 Ni Ni+2 + 2e- 0.25 FeO -244.4 Zn Zn+2 + 2e- 0.76 SnO -257.3 Al Al+3 + 3e- 1.66 Mg Mg+2 + 2e- 2.37 1 SPONTANEOUS REDUCTION OF + SILVER (Ag ) by COPPER METAL PRODUCTION OF COPPER BY PRECIPITATION WITH METALLIC IRON “HELVA MINES” GÜMÜŞHANE HELVA MINE REDUCTION OF CuO BY Fe METAL Is it possible?? Cu+2 Cu (Metal) Eo = +0.34 volts Fe (Metal) Fe+2 Eo = +0.44 volts Cu+2 + Fe Cu + Fe+2 Eo = +0.78 volts 2 Color of water after precipitation Yellow-orange color is FeO (Rust) 3 Cu+2 + 2e- Cu Fe Fe+2 + 2e- Cu+2 + Fe Fe+2 + Cu The blue-Green color is due to the dissolved Cu+2 ions in water. It is leaceh from the spoils by acidic water. 4 REDUCTION OF METAL OXIDES BY CARBON MONOXIDE COMBUSTION OF CARBON 1. Reduction of metal ore with CO 2C + O2 2CO2 MO + CO M + CO2 CO2 C + O2 2. Conversion of CO2 back to CO ___________________________ C + CO 2CO 2 C + CO2 2CO At 710 oC, DG = DH - TDS = 0 T>710 oC, Equilibrium shifts to right T<710 oC, Equilibrium shifts to left ELLINGHAM DIAGRAM FOR ELLINGHAM DIAGRAM FOR Zn, Ni, Mg, Mn, and Al Ag, Hg, Sn, Cu, Pb and Fe 5 ELLINGHAM DIAGRAM EVIDENCE FOR ANCIENT SMELTING 1. Lower the position of the metal oxide greater is the affinity for oxygen. • Generally carried out near mines 2. Free energy (DG) of most elements decrease by increasing temperature. • Remains of slags are mostly visible 3. The slope of carbon line is opposite of others • Other smelting tools such as bellows, 4. Any metal oxide with line above that of carbon tuyers, molds, prills may be found. can be reduced by carbon at proper temperature. • Possible furnace structures may be 5. More stable metal oxides at the lower section cannot be reduced by carbon (Al, Ca, Mn) existing http://www.jfe-21st-cf.or.jp/chapter_2/2b_1/html MERZİFON BAKIRÇAY SLAGS GÜMÜŞHANE KARADAĞ 6 GÜMÜŞHACI KÖY SLAG HEAP REQUIREMENTS FOR SMELTING • A furnace that can reach high enough temperatures • Fuel to supply the heat needed • Bellows to reach temperatures over 10000C • Generation of reducing gas (CO) that can reduce the metal oxide to metal • Fluxing agents to reduce the melting point of rocks and minerals BOWL FUENACE SMELTING FURNACES • Bowl or crucible process • Shaft furnace process • Reverberatory furnace process (not used in antiquity) 7 SMELTING CRUCIBLES SMELTING CASSITERITE IN A CRUCIBLE Metalik kalay tanecikleri ANCIENT SHAFT FURNACE BOWL FURNACE 8 CRUCIBLE SMELTING ANCIENT BOWL FURNACE SHAFT FURNACE FURNACE WHERE SLAG CAN BE TAPPED 9 SMELTING FURNACE WITH TAPPING SHAFT FURNACE From Agricola FUELS FOR SMELTING CHARCOAL MAKING 1. Wood: Used extensively in antiquity 2. Charcoal: Made by removal of volatile components of wood under reducing atmosphere. Extensively and efficiently used in smelting. 3. Coal: Volatile constituents spoiled the smelting process 4. Coke: Made by the distillation of coal in the absence of air. Best fuel for the production of iron in blast furnace. 10 CHARCOAL REQUIREMENT FOR SMELTING • Charcoal to copper ratio for smelting oxide ores is between 1:30. • To prepare 5 Kg of copper one needs 150 Kg of charcoal. • Over 1000 Kg of fresh wood would be needed to prepare 150 Kg of charcoal. • This will take almost 5 man days of labor 11 BLOW PIPES AIR SUPPLY TO REACH HIGH TEMPERATURES USE OF BLOW PIPES IN ANCIENT TUYERS FOR BLOW PIPES SMELTING FURNACES Human lungs can produce intermitent flow of 40 l/min and 10-20 l/min on continuous basis. This can heat a small area over 1000 oC. 12 WHAT TEMPERATURE CAN BE WHAT TEMPERATURE CAN BE BREATH COMPOSITION ATTAINED BY HUMAN BREATH? BREATH COMPOSITION • GIVEN: 70 Kg person who can sustain an Breathing % H O % O % CO 2 % N average expelled breath volume of 75 Effort 2 2 (Vapor) 2 liter/min. (0.075 m3/min) • PURPOSE: To maintain a temperature of • PURPOSE: To maintain a temperature of Quite 15.4 3.8 6.0 74.8 1200oC, in a furnace with 25 cm internal diameter (0.049 m2) • REQUIREMENT: 3 m3/m2 min of air. Deep 13.0 5.2 6.0 75.8 BLOWPIPE GENERATION OF HEAT GENERATION OF HEAT USING A BELLOW Needed air flow rate = (0.049 m2)(3 m3/m2 min) = 0.147 m3/min Heat generated/min = (0.147 m3/min)(2 MJ/m3) = 0.29 MJ/min • Muscular mechanic power output of a 75 Kg Average human breath generate approximately 1.3 MJ/min person is 170 watts. 0.29 MJ/min • Human power can generate 18 watts of gas Flow rate of air needed = = 0.22 m3/min flow with a 15 % efficient bellow. 3 1.3 MJ/m • 18 watts can generate an air flow rate of Number of persons needed = 0.22 m3/min/0.073 m3/min person 3.6 m3/min, which is equivalent to 7.1 MJ/min. = 3 Persons • Thus one person can generate 73 times more Thus to maintain a furnace of 25 cm internal diameter at 1200oC, heat by using a bellow compared to blowpipe. Three persons are needed by using blowpipe 13 BAG BELLOW TUYERS FOR BELLOWS OPERATION OF POT BELLOW OPERATION OF TUYER WITH A TUYER 14 OPERATION OF POT BELLOW POT BELLOWS POT BELOW FROM DIFFERENT ARCHAEOL- OGICAL SITES Kültepe, Kayseri. Dated to 1900 BC Acemhöyük, Aksaray. Dated to 1900 BC 15 PISTON BELLOW 16 BELLOW (FROM AGRICOLA) FLUXES USED IN SMELTING GENERATION OF HEAT USING A Fluxes are materials added to smelting furnace to reduce the BELLOW melting point of the charge. During smelting, fluxing agents Combine with the unwanted infusible siliceous materials to • Muscular mechanic power output of a 75 Kg Form a fusible mass called slag person is 170 watts. Components of slags: • Human power can generate 18 watts of gas • Basic Oxides such as CaO, MnO, MgO, FeO, ZnO, PbO, N2O, K2O which provide oxygen ions when dissolved in flow with a 15 % efficient bellow. a slag. • 18 watts can generate an air flow rate of +2 -2 3.6 m3/min, which is equivalent to 7.1 MJ/min. MO M + O • Thus one person can generate 73 times more • Acidic Oxides such as SiO2 that absorbs oxygen ions provided heat by using a bellow compared to blowpipe. by the basic oxides. -2 -4 SiO2 + 2O SiO4 17 COMPOSITION FLUX COMPOSITION OF SLAGS (CaAl2Si2O8) A proper balance of iron oxides (basic) and silicates (acidic) during copper smelting can produce a fluid slag known as Fayalite (Fe2SiO4). nMO - 3(nAl2O3) + nP2O5 Basicity of Slag = 2nSiO2 Copper matte smelting produce slag that contains about 50% FeO and 38% SiO2 which gives a basicity value of 0.48. FeO SiO2 TYPES OF SLAGS • FAYALITHIC SLAG (Formed in bloomery furnace where wrought iron is produced) • GLASSY SLAG (Formed in blast furnaces where cast iron is produced) • FINARY SLAG (Formed in fineries where cast iron is converted into wrought iron) 18 FAYALITHIC SLAG (Iron slag) ANALYSIS OF SLAG • Elemental composition is determined by Gen. Comp. AAS, ICPE, Neutron activation FeO: 60.5 SiO2: 22.0 • Mineralogical analysis is determined by CaO: 3.75 Al2O3: 5.86 XRD, petrological microscope • Microstructure is determined by optical microscopy, SEM Fayalite FeO : 43.9% IMPURITIES IN COPPER ORES SiO : 18.4% IMPURITIES IN COPPER ORES 2 Wüstite CaO: 1.75% FeO : 67.1% Al2O3: 0.87% SiO2 : 1.79% • Most copper ores contain certain amount of CaO: 0.34% impurities such as As, Sb, Bi, Pb, Ag, Au, Ni, Co Al2O3: 1.28% and Zn. • Trace elements from fuel, fluxes furnace lining may also enter the metal during smelting. Anorthite • Iron is the major impurity since it is added as a FeO : 12.6% fluxing agent, copper obtained from low grade SiO2 : 22.1% CaO: 4.54% ores may have 2-10 % Fe. Al2O3: 10.3% • These elements will partition between the metal and the slag depending on the smelting conditions. 19 The impurities in copper ores OTHER SOURCES OF MINOR AND TRACE ELEMENTS IN COPPER partition between the metal and slag SLAG METAL BOTH • Deliberate additions to form alloys at metal Fe Co Zn Mn Ni As* working centers (As, Sn, Sb, Pb, Zn) Pb Sb* • Trace elements from fuel, fluxes and ore Ag which enter the metal during smelting. Fe is Au especially diagnostic) * Volatile elements. 20.
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