pyrometallurgy basica
TRANSCRIPT
Chapter 3: Metal Synthesis and Processing
3.1 Introduction3.2 Ellingham diagrams3.3 Pyrometallurgy of iron and steel3.4 Primary copper production3.5 Primary aluminum production3.6 Other synthesis routes
Relative importance of different materials
7000 years ago, prehistoric people discovered methods of heating minerals to extract tin, lead and other metals.Human passed from Stone age to Bronze age. Then they found the use of iron and created Iron Age.
Metal ores
Cinnabar, HgS; Rutile TiO2 in a quartz matrix, and Gold embedded in quartz.
盐
Cinnabar (朱砂) and rutile (金红石)
chirality
Synthesis methods for metals
1) Metallurgy (冶金,冶金学): ores metals• Powder metallurgy (粉末冶金) (mostly processsing)• Pyrometallurgy (热冶金,火法冶金)• Hydrometallurgy (湿法冶金)
2) Electrowinning (电解冶金)and electrorefinning (电解精炼)
3) Electroplating (Electrodeposition) (of metal films)
4) Electroless plating (Electroless deposition)(化学镀,无电镀)
5) Mechanical alloying
6) Plasma spraying
7) CVD/PVD
Electrochemistry basics
• The amount of electricity that flows through the cell depends on the amount of species being oxidized or reduced according to the Faraday law:
AMnFitm =
n- number of electrons in a redox reaction, N-number of moles,MA- molecular weight, F- Faraday constant (96485C/mole)
I = dQ/dt Q = ∫Idt• Electricity:
ΔG0 = -nFE0 ΔG = -nFE E=E0 – (RT/nF)lnQΔrS = nF(∂E/∂T)P ΔrH = -nFE + nFT(∂E/∂T)P
• In an electrochemical reaction: aA + bB == gG + hH
ΔGocell = -nFEo
cell
Eocell= Eo
cathode – Eoanode
If Eocell> 0, then the
process is spontaneous (galvanic cell)
If Eocell< 0, then the
process is nonspontaneous(electrolytic cell)
Pyrometallurgy of metals
Ellingham diagram
Ellingham diagram
Construction of an Ellingham diagram
An Ellingham diagram is a plot of ΔG0 versus temp. Since ΔH and ΔS are essentially constant with temp. Unless a phase change occurs, and ΔG = ΔH-TΔS, the ΔG0~T plot can be drawn as a series of straight lines, where ΔS is the slope and ΔH is the y-intercept.
The Ellingham diagram is for metals reacting to form oxides (similar diagrams can also be drawn for metals reacting with sulfur, chlorine, etc., but the oxide form of the diagram is most common). The oxygen partial pressure is taken as 1 atmosphere, and all of the reactions are normalized to consume one mole of O2.
Features of Ellingham diagram
1) The majority of the lines slope upwards with an approximately same slope.
2) The slope of a line changes when there is a phase change.
3) Under standard states, all metals with negative value of ΔG may be oxidized spontaneously. The oxides with positive ΔG is not stable and are easily decomposed to elemental metals.
4) A given metal can reduce the oxides of other metals whose lines lie above theirs on the diagram.
Richardson-Ellingham diagram
Closer look at Ellingham diagram
Ellingham diagram
HC
0K
ΔG0 =
RTl
nPO
2
0
0 400 800 1200 1600
1
10-4
10-8
10-12
10-16
10-20
10-24
10-28
C + O2 = CO2
2M + O2 = 2MO
PO2 (atm)T (K)
Three main uses of the Ellingham diagram
1) Determine the relative ease of reducing a given metallic oxide to metal;
2) Determine the partial pressure of oxygen (PO2) that is in equilibrium with a metal oxide at a given temperature;
3) Determine the ratio of carbon monoxide to carbon dioxide (PCO/PCO2) that will be able to reduce the oxide to metal at a given temperature.
Online tutorials on Ellingham diagramshttp://www.engr.sjsu.edu/ellingham/tutorial.html (San Jose State Univ)http://www.doitpoms.ac.uk/tlplib/ellingham_diagrams/index.php (Cambridge)
Similar diagram with CO2 reactions
100 100
0 0
-100 -100
-200 -200500 5001000 10001500 1500
T / K T / K
ΔrG
0 / kJ⋅m
ol-1
ΔrG
0 / kJ⋅m
ol-1
SrTiO3
SrZrO3
SrCeO3
SrO
BaTiO
BaZrO3
BaCeOBaO
SrTiO3,SrZrO3等钙钛矿在高温下能在CO2气氛中稳定存在。
ABO3(s) + CO2(g) = ACO3(s) + BO2 (s)
Abundance of elements in Earth's crust
Compound Composition
SiO2 59.71%
Al2O3 15.41%
CaO 4.90%
MgO 4.36%
Na2O 3.55%
FeO 3.52%
K2O 2.80%
Fe2O3 2.63%
H2O 1.52%
TiO2 0.60%
P2O5 0.22%
Total 99.22%
Fe: 5.63% Al: 8.23% Cu: 0.006%
http://www.jfe-21st-cf.or.jp
Pyrometallurgy of iron and steel
Heat treatment procedure for iron production
• Drying: @~100°C, to remove mechanically bounded
H2O
• Calcination: @>900°C, to drive off CO2 from limestone.
CaCO3(s) CaO(s) + CO2(g)
• Roasting: to convert sulfides to oxides
2ZnS(s) + 3O2(g) 2ZnO(s) + 2SO2(g) (ΔH=-211kcal)
4FeS2(s) + 11O2 2Fe2O3(s) + 8SO2(g) (ΔH=-796kcal)
• Smelting: to let the material melts and produce a
molten melt and a slag. The impurities are either carried
off by the slag, or are burned off as a gas.
Iron ore and its pretreatment
Coal and coking
Indirect heating at 1,473-1,573K (1,200-1,300oC ) for 14-18h
Blast furnace (BF)
BF operation
Iron blast furnace
Iron blast furnace
Slag: SiO2+Si+CaS
Hot metal pretreatment
Basic Oxygen Furnace (BOF)
BOF operation
Direct reduction process
Electric Arc Furnace (EAF)
Secondary refining
Continuous casting
Continuous casting
Continuous caster operation
Pyrometallurgical equipment
Shaft furnace (竖炉 )
Muffle furnace
Hearth furnacesA. Reverberatory(反射炉 );
B. B. Rotary(回转炉 )
Electric furnace
Roasters
Flash/suspension roaster(悬浮焙烧炉 )
Fluid bed roaster
(流化床焙烧炉 )
Hearth Roaster(床式焙烧炉 )
Steel productionIntegrated steel mill and electric-arc furnace minimill
Comparison between pig iron and steel
<0.04%0.025-2.5%Phosphorus
0.02-0.04%Up to 0.2%Sulfur
Trace0.5-4%Silicon
0.3-0.9%0.15-2.5%Manganese
0.04-1.7%3-4%Carbon
SteelPig Iron
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(a) The eutectoid portion of the Fe-Fe3C phase diagram. (b) An expanded version of the Fe-C diagram, adapted from several sources.
T-T-T diagram
Electron micrographs of (a) pearlite, (b) bainite, and (c) tempered martensite, illustrating the differences in cementite size and shape among these three microconstituents (× 7500).
Flame surface hardening
• Heat the surface of a steel part rapidly to a temperature above the critical point of the steel → form austenitic grain structure (austenitized) → quickly quench (water or force air) to transform austenite to martensite → form a hard case (the core of the part in its original state: ferrite and pearlite);
• Requirements: hardenable carbon steels (wrought or cast, 0.37-0.55%C) and cast irons (0.35-0.80%C), martensitic stainless steels, tool steels, steels with adequate carbon and other alloy elementaddition.
Relationship of carbon content to minimum surface hardness attainable by flame heating and water quenching
Flame surface hardening
Spinning methods of flame hardening. In methods shown at left and at center, the part rotates. In method at right, the flame head rotates.
Combination progressive-spinning flame hardening.
Primary copper production
Copper Pyrometallurgical Reactions(Assuming a feed contains no sulfides other than chalcopyrite CuFeS2)
• Roasting: (500-700°C)CuFeS2 + 4O2 ==> CuSO4 + FeSO4
2CuFeS2 + 13/2O2 ==> 2CuO + Fe2O3 + 4SO2
• Smelting: (1200°C)FeS + 6CuO ==> 3Cu2O + FeO + SO2
FeS + Cu2O ==> FeO + Cu2S
Cu2S + FeS ==> Cu2S•FeS (matte)
• Coverting reactions: to convert matte to copper.
(silica is added as a flux)2Cu2S•FeS + 3O2 + SiO2 ==> 2FeO•SiO2 + 2SO2 + Cu2S
Cu2S + O2 ==> 2Cu + SO2
• Fire-refinning reactions:4CuO + CH4 ==> Cu + CO2 + 2H2O
Pierce-Smith copper converter
During the converting process, air is injected
through the tuyeres(风口 ), and off-gases are collected by a removablehood that covers the charging port. The tuyeresare equipped with pneumatic“punchers” to break throughany slag or other solids that may solidify over thetuyere opening.
Outokumpu flash smelting process
Sulfide concentrate is injected through a burner along with preheated air, and partially burned as it falls through a flash-roasting zone. The heat produced by roasting the sulfide helps to melt the concentrate, with supplemental fuel injected into the flash-roasting area to provide the remaining heat.
Integrated flash smelting/flash converting copper production facility.
Hydrometallurgy
Hydrometallurgy of copper
Advantages:
• Producing little pollution
• Saving energy
• Treatment is carried out at a low temperature
• Liquid effluent consists of chemical compounds that are easy to reprocess and recover.
• Well suited to extracting metal from low-grade ores.
Hydrometallurgy of copper: leaching
A. Dump leaching
B. Heap leaching
Leaching reagents = acids, complexing agents, oxidizers, etc.
Leaching reactions
• Non-oxidative reactions:
CuSO4(s) + H2O(l) ===> Cu+2(aq) + SO4-2(aq)
Cu2(OH)2•CO3(s) + 2H2SO4(aq) ===> 2CuSO4(aq) + CO2 + 3H2O
• Oxidative leaching:CuS(s) + 2O2(g) ===> CuSO4(aq)
4H2O + CuS(s) + 4Fe2(SO4)3(aq) ===> CuSO4(aq) + 8FeSO4 (aq) + 4H2SO4
• Bacterial leaching:
Thiobacillus ferrooxidans (硫杆菌):
to oxidize pyrite (FeS2) to leaching reagents.
Bacteria
4FeS2(s) + 15O2 + 2H2O ======> 2Fe2(SO4)3(aq) + 2H2SO4(aq)
Solution purification
• Ion-exchange reagent:
Metal recovery
• Cementation (置换沉淀法):Dissolved copper will plate out on an iron surface due to:
Cu+2(aq) + Fe(s) ===> Fe+2(aq) + Cu(s)
A. Electrowinning B. Electrorefinning
• Electrowinning: electrochemically precipitate metals from solution.
Cu+2(aq) + 2e- ===> Cu(s)
• Electrorefinning: from impure copper (generally from the fire-refiningstage in a pyrometallurgical operation) is cast into copper anodes.
Complete layout of the hydrometallurgy of copper
Hydrometallurgy of zinc (Zn), gold (Au) and silver (Ag)
Hydrometallurgy of zinc (Zn), gold (Au) and silver (Ag)
Hydrometallurgy of titanium (Ti)
Primary aluminum production
The primary ore of aluminum: bauxite (铝矾土)
a mixture of hydrated aluminum oxides:
• Gibbsite - Al(OH)3 (most extractable form)
水铝矿
• Boehmite – γ-AlO•OH (less extractable than Gibbsite)
水软铝石,勃姆石
• Diaspore – α-AlO•OH (difficult to extract)
水铝石
Bayer process for alumina production
• Dissolution: (in autoclave)Al(OH)3 + NaOH ==> NaAlO2 + 2H2O (Gibbsite dissolution)
(150-255 g/L Na2CO3 , 100-150°C, 3.8-5 atm)
AlO•OH + NaOH ==> NaAlO2 + H2O (Boehmite dissolution)
(205-445 g/L Na2CO3 , 200-315°C, 19-100 atm)
• Precipitation: (room temp., with Al(OH)3 seed)
NaAlO2 + 2H2O ==> Al(OH)3 + 2NaOH
• Calcination: (1300-1500°C)
2Al(OH)3 ==> Al2O3 + 3H2O
Bayer process flowsheet-The "Bayer Process" used at Sherwin
Hall-Heroult process for aluminum production (1886)
• Dissolution: (935-975°C)
Dissolving Al2O3 in molten cryolite (Na3AlF6, 冰晶石)
• Electrolysis: (4-5V vs. 1.15V Etheo)
2Al2O3 + 3C ==> 4Al + 3CO2
Hall-Heroult process for aluminum production (1886)
Electrometallurgy of other metals
Copper
Sodium
Cu2+(aq) + 2e- Cu(s) E°red = +0.34V
Ni2+(aq) + 2e- Ni(s) E°red = -0.28V
2H2O(l) + 2e- H2(g)+ 2OH- E°red = -0.83V2H+(aq) + 2e- H2(g) E°red = -0.00V
Production of Li
LiCl
Li
Method 1. Electrometallurgy
Method 2. Pyrometallurgy
a) 2Li2O + Si = 4Li + SiO2 ∵ΔG0
278 = + 298 kJ,ΔH0298 = + 320kJ) ∴ High temp. + Vacuum: Li(g)
Li2CO3
b)
c)
Production of Li
周园等,《稀有金属》,28(2)(2004)343.
Powder Metallurgy
MN (825 ton) mechanical press
Powder Metallurgy
Distribution of P/M parts in a car
Advantages of P/M:•Metal powders are high-purity materials •Close dimensional tolerances can be maintained •High-volume process with excellent reproducibility •Quality control is inherent in the process •Low labor input •Machining is eliminated or reduced •Scrap losses are eliminated or reduced •Segregation is avoided •Controllable porosity and density can be precisely controlled •Combines immiscible metals •Complex shapes can be produced
Disadvantages of P/M:• costs of powder production• limitations on the shapes and features, e.g. re-reentrant angles by fixed die pressing or radial holes in vertically pressed cylinders• the size will always change on sintering.
Powder Metallurgy
FINISHEDPRODUCTS
P/M ProcessOPTIONAL
OPERATIONSSINTERINGFORMINGMIXINGRAWMATERIALS
Elemental orAlloy Metal
Powders
Additives(graphite, die,
lubricants)
Mixing
IsostaticExtrusion
Die CompactingSpraying
Pressureless-Sintering
Die CompactingIsostaticRolling
Injection MoldingSlip Casting
Cold Compaction
Hot Compaction
AtmosphereVacuum
High Temperature
SinteringRepressing
ConingSizing
RepressingForging
RerollingMetal Infiltration
OptionalManufacuring Steps
MachiningHeat Treating
Steam TreatingPlastic Impregnation
PlatingTumbling
Oil ImpregnationShot Peening
OptionalFinishing Steps
FinishedProducts
粉末冶金生产工艺
Powder production
• Mechanical comminution(top-down)
• Electrolytic deposition(bottom-up)
• Chemical reactions(bottom-up)
• Atomization(top-down)
喷射沉积
Stone mills
挤压
拉拔
轧制
A typical compaction cycle
连铸连轧
连续挤压conform
Mechanical Alloying
C.C. Koch, “Intermetallic matrix composites prepared by mechanical alloying—a review”, Mater. Sci. Eng. A244 (1998) 39-48.
Au-Ag 1970's, International Nickel Co. (INCO)
dispersing nanosized oxide inclusions into Ni-based alloys
Mechanical Alloying equipment: shaker and planetary mills
Planetary ball mill
Shaker mill
Mechanical Alloying equipment: Attritors
100-500rpm
Low energy ball mill
Most ball mills operate most efficiently between 65% ~75% of their critical speed.
Low energy ball mill
Jet mills
Jet mill
Jet mills and other mills
Jet mill, 0.1~1 μm,tight PSD
Air-swept impact mill, ~1 μm, tightest PSD
Centrafugalpin-type impact mill, 50~200 mesh
Air claasifier Hammer millfor friable materials
Roll crusherfor friable materials
Jaw crusherCoarse and intermediate crushing
Rotary crusherRugged rotary action with high reduction ratios and production rates. Soft-to medium hard materials
Sample grinderwith small throughput rates
“x” mesh = 25.4/x mm
Plasma spraying
Spray conversion process
Preparation of metallic glass-Melt spinning
It is possible to rapidly quench a molten metallic alloy, thereby bypassing crystallization, and forming a glassy metal commonly called a metallic glass. The process is called melt spinning.
Preparation of metallic glass-Melt spinning
Cooling 105-106K/s
Metglas: Fe-Si-B, Fe-Ni-P-B, …
Liquidmetal®(Zr41.2Be22.5Ti13.8Cu12.5Ni10.0)