R. M. Cornell, U. Schwertmann
The Iron Oxides
Structure, Properties, Reactions,
Occurences and Uses
Second, Completely Revised and Extended Edition
R. M. Cornell, U. Schwertmann
The Iron Oxides
Also of interest
U. Schwertmann, R. M. Cornell
Iron Oxides in the Laboratory
2nd edition 2000
ISBN 3-527-29669-7
C. N. R. Rao, B. Raveau
Transition Metal Oxides
2nd edition 1998
ISBN 0-471-18971-5
J.-P. Jolivet, M. Henry, J. Livage
Metal Oxide Chemistry and Synthesis
1st edition 2000
ISBN 0-471-97056-5
R. M. Cornell, U. Schwertmann
The Iron Oxides
Structure, Properties, Reactions,
Occurences and Uses
Second, Completely Revised and Extended Edition
Authors
Dr. R. M. Cornell
Universität Bern
Departme nt für Chemie und Biochemie
Freiestrasse 3
3000 Bern 9
Switzerla nd
Prof. em. Dr. Dr. h.c. U. Schwertmann
Technis che Universität München
Institut für Bodenk unde
85354 Freising
Germany
& This book was carefu lly produced. Never-
theless, authors and publisher do not warrant the inform ation contained therein to be
free of errors. Readers are advised to keep in
mind that statements, data, illustrations,
procedural details or other items may
inadverte ntly be inaccura te.
Library of Congress Card No.: Applied for:
British Library Cataloguing-in-Publication
Data : A catalogue record for this book is
available from the British Library.
Bibliographic information published by
Die Deutsche Bibliothek
Die Deutsche Bibliothek lists this publication
in the DeutscheNationalbibliografie;
detailed bibliog raphic data is available in the
Internet at <http://dnb.ddb.de>.
 2003 WILEY-VCH Verlag GmbH & Co.
KGaA, Weinheim
1st Edition 1996
1st Reprint 1997
2nd Reprint 1998
2nd Edition 2003
Cover Illustration
Prehistoric cave painting of a red horse from
Lascaux. The colours used in the painting
were obtained from the local depo sits of red
and yellow ochres, i. e. iron oxides. Similar
ochre deposits in Southern France are still
mined for pigment production today. As
colouring agents, iron oxides have serve d
man more or less continuously for over
30,000 years. A major , modern technological
application of these compounds (mainly in
synthetic form) is as pigment.
(Courtesy of Musée National de Préhistorie
Les Eyzies).
All rights reserved (including those of translation in other languages). No part of this
book may be reproduced in any form – by
photoprinting, microfilm, or any other
means– nor transmitted or translated into
machine language without written permission from the publishers. Registered names,
trademarks, etc. used in this book, even
when not specifically marked as such, are
not to be considered unprotect ed by law.
Printed on acid-freepaper
Composition ProSatz Unger, Weinheim
Printing Druckhaus Darmstadt,Darmstadt
Bookbinding Litges & Dopf, Heppenheim
Printed in the Federal Republic of Germa ny
ISBN
3-527-30274-3
V
Contents
1
Introduction to the iron oxides 1
2
2.1
2.2
2.2.1
2.2.2
2.3
2.3.1
2.3.1.1
2.3.1.2
2.3.1.3
Crystal structure 9
General 9
Iron oxide structures 9
Close packing of anion layers 10
Linkages of octahedra or tetrahedra 13
Structures of the individual iron oxides 14
The oxide hydroxides 14
Goethite a-FeOOH 14
Lepidocrocite c-FeOOH 18
Akaganéite b-FeOOH and schwertmannite
Fe16O16 (OH)y(SO4)z · n H2O 20
d-FeOOH and d'-FeOOH (feroxyhyte) 22
High pressure FeOOH 23
Ferrihydrite 23
The Hydroxides 27
Bernalite Fe(OH)3 · n H2O 27
Fe(OH)2 27
Green rusts 28
The Oxides 29
Hematite a-Fe2O3 29
e-Fe2O3 31
Magnetite Fe3O4 32
Maghemite c-Fe2O3 32
Wüstite Fe1–xO 34
The Fe-Ti oxide system 37
Appendix 37
2.3.1.4
2.3.1.5
2.3.1.6
2.3.2
2.3.2.1
2.3.2.2
2.3.2.3
2.3.3
2.3.3.1
2.3.3.2
2.3.3.3
2.3.3.4
2.3.3.5
2.4
3
3.1
3.2
3.2.1
Cation substitution 39
General 39
Goethite and lepidocrocite 42
Al substitution 42
VI
Contents
3.2.2
3.3
3.3.1
3.3.2
3.4
3.5
Other substituting cations 47
Hematite 51
Al substitution 51
Other cations 54
Magnetite and maghemite 55
Other iron oxides 57
4
4.1
4.1.1
4.1.2
4.1.3
4.2
4.2.1
4.2.1.1
4.2.1.2
4.2.1.3
4.2.1.4
4.2.2
4.2.3
4.2.4
4.2.5
4.2.6
4.2.7
4.2.8
Crystal morphology and size 59
General 59
Crystal growth 59
Crystal morphology 60
Crystal size 62
The iron oxides 63
Goethite 64
General 64
Domainic character 69
Twinning 71
Effect of additives 73
Lepidocrocite 74
Akaganéite and schwertmannite 75
Ferrihydrite 78
Hematite 81
Magnetite 87
Maghemite 92
Other Iron Oxides 94
5
5.1
5.2
5.3
5.4
5.4.1
5.4.2
5.4.3
5.4.4
5.4.5
5.4.6
5.4.7
5.4.8
Surface area and porosity 95
Surface area 95
Porosity 98
Surface roughness and fractal dimensions 100
The iron oxides 101
Goethite 102
Lepidocrocite 103
Akaganéite and schwertmannite 104
d-FeOOH and feroxyhyte 105
Ferrihydrite 106
Hematite 108
Magnetite 109
Maghemite 109
6
6.1
6.1.1
6.1.2
6.1.3
Electronic, electrical and magnetic properties and colour 111
Electronic properties 111
Free Fe3+ and Fe2+ ions 111
Bound Fe ions 112
Molecular orbital description of bonding in iron oxides 113
Contents
6.2
6.2.1
6.3
6.3.1
6.3.2
6.3.3
6.3.4
6.3.4.1
6.3.4.2
6.3.4.3
6.3.4.4
6.3.4.5
6.3.4.6
6.3.4.7
6.3.4.8
6.4
6.4.1
6.4.2
6.4.3
Electrical properties 115
Semiconductor properties of iron oxides 116
Magnetic properties 118
Basic definitions 118
Types of magnetism 119
Magnetic behaviour of iron oxides 121
The different iron oxides 123
Goethite 123
Lepidocrocite 124
Akaganéite 124
d-FeOOH, feroxyhyte and high pressure FeOOH 125
Ferrihydrite 125
Hematite 126
Magnetite and maghemite 128
Other Fe oxides 130
Colour 130
General 130
Colours 133
Pigment properties 136
7
7.1
7.2
7.2.1
7.2.2
7.2.3
7.2.4
7.2.5
7.3
7.4
7.4.1
7.4.2
7.5
7.5.1
7.5.2
7.5.2.1
7.5.2.2
7.5.2.3
7.5.2.4
7.5.2.5
7.6
7.6.1
7.6.2
7.6.3
7.6.4
Characterization 139
Introduction 139
Infrared spectroscopy 141
Goethite 141
Lepidocrocite 144
Ferrihydrite 144
Hematite 145
Other iron oxides 146
Raman spectroscopy 146
Ultraviolet-visible spectroscopy 147
General 147
Spectra of the different Fe oxides 148
Mössbauer spectroscopy 152
General 152
Spectra of the various Fe oxides 157
Goethite and lepidocrocite 157
Ferrihydrite 157
Hematite 158
Magnetite and maghemite 158
Other iron oxides 160
Magnetic properties (Magnetometry) 161
General 161
Magnetic susceptibility v 162
Magnetic anisotropy, coercivity and saturation magnetization 163
Domain type 164
VII
VIII
Contents
7.6.5
7.6.6
7.7
7.7.1
7.7.2
7.8
7.8.1
7.8.2
7.9
7.10
7.11
Curie temperature analysis 167
Applications 167
Other spectroscopic techniques 168
Photoelectron spectroscopy 169
X-ray absorption spectroscopy 171
Diffractometry 172
X-ray diffraction 172
Other diffraction techniques 177
Microscopy 179
Thermoanalysis 181
Dissolution methods 183
8
8.1
8.2
8.3
8.4
8.5
8.5.1
8.5.2
Thermodynamics of the Fe-O 2-H2O system 185
General 185
Standard free energy of reaction and the equilibrium constant 186
Redox reactions 189
Effect of complexing agents on redox potential 192
Stabilities of iron oxides 193
“Bulk” crystals 193
Effect of particle size and Al substitution 197
9
9.1
9.2
9.3
9.4
9.4.1
9.4.2
9.4.3
9.4.4
9.4.4.1
9.4.4.2
9.5
9.6
Solubility 201
General 201
The solubility product 201
The effect of hydrolysis reactions and pH on solubility 203
Other factors influencing solubility and the solubility product 208
Complexation 208
Redox reactions 209
Ionic strength 211
Properties of the solid 211
Particle size 211
Ageing and isomorphous substitution 214
Methods of determining or calculating the solubility product 214
Solubility products of the various oxides 217
10
10.1
10.2
10.3
10.4
10.5
10.5.1
10.5.2
10.6
10.7
Surface Chemistry and Colloidal Stability 221
Surface functional groups 221
Surface acidity and acidity constants 227
The electrical double layer and electrochemical properties 232
Point of zero charge 236
Stability of colloidal suspensions 241
General 241
Stability of iron oxide suspensions 243
Tactoids, gels and schiller layers 250
Rheological properties 250
Contents
11
11.1
11.2
11.2.1
11.2.2
11.3
11.3.1
11.3.2
11.3.2.1
11.3.2.2
11.3.2.3
11.4
11.4.1
11.4.2
11.5
11.5.1
11.5.2
11.5.3
11.5.4
11.6
11.7
11.8
Adsorption of Ions and Molecules 253
General 253
Treatment of adsorption data 254
The Langmuir, Freundlich and Temkin isotherm equations 254
Surface complexation models 255
Anion adsorption 258
Modes of coordination 265
Examples of inorganic ligands 267
Phosphate 267
Other anions 270
Organic anions and other organic compounds 273
Cation adsorption 279
General 279
Examples of cations 284
Adsorption from mixed systems 288
Competition between anions 289
Competition between cations 289
Interactions between cations and anions 290
Ternary adsorption 290
Adsorption of water 293
Adsorption of gases 293
Photochemical reactions 295
12
12.1
12.2
12.2.1
12.2.2
12.2.3
12.2.4
12.2.4.1
12.2.4.2
12.2.4.3
12.2.4.4
12.2.5
Dissolution 297
Introduction 297
Dissolution reactions and mechanisms 298
General 298
Protonation 299
Complexation 301
Reduction 306
General 306
Examples of reductants 312
Photochemical reduction 316
Biological and other reduction reactions 319
Comparison of the three different types of dissolution
reactions 323
Dissolution equations 324
Individual iron oxides 326
Goethite 328
Unsubstituted goethite 328
Substituted goethite 330
Natural goethite and hematite 332
Lepidocrocite and akaganéite 334
Ferrihydrite 335
Hematite 337
12.3
12.4
12.4.1
12.4.1.1
12.4.1.2
12.4.1.3
12.4.2
12.4.3
12.4.4
IX
X
Contents
12.4.5
12.4.6
Magnetite and maghemite 338
Comparison of different oxides 339
13
13.1
13.2
13.2.1
13.2.2
13.3
13.3.1
13.3.2
13.3.3
13.3.4
13.4
Formation 345
General 345
Formation in FeIII systems 347
Hydrolysis reactions 347
Formation of the different FeIIIoxides 350
Formation in aqueous FeII systems 355
General 355
Effect of pH 356
Effect of oxidation rate 359
Effect of foreign compounds 360
Decomposition of Fe complexes 363
14
14.1
14.2
14.2.1
14.2.2
14.2.3
14.2.4
14.2.5
14.2.6
14.2.7
14.3
14.3.1
14.3.2
14.3.3
14.3.4
14.3.5
14.3.5.1
14.3.5.2
14.3.5.3
14.3.5.4
14.3.5.4.1
14.3.5.4.2
14.3.5.4.3
14.4
14.4.1
14.4.2
14.4.3
14.5
Transformations 365
Introduction 365
Thermal transformations 367
General 367
Goethite to hematite 369
Lepidocrocite to maghemite or hematite 373
Akaganéite and schwertmannite to hematite 375
d-FeOOH and feroxyhyte to hematite 378
Ferrihydrite to hematite 378
Interconversions between maghemite and hematite 382
Via solution transformations 383
Lepidocrocite to goethite/hematite 383
Akaganéite to goethite/hematite 384
Schwertmannite to goethite 385
Maghemite and goethite to hematite 386
Ferrihydrite to other Fe oxides 388
Rate of transformation 388
Hematite versus goethite formation 390
Mechanism of transformation 391
Effect of foreign compounds 393
General 393
Anions and neutral molecules 395
Cations 398
Oxidative and reductive transformations 402
Oxidation of magnetite to maghemite or hematite 402
Reduction of FeIII oxides to magnetite 405
Reduction of iron ores to iron 406
Interaction of iron oxides with other metal oxides and carbonates 407
Contents
15
15.1
15.2
15.3
15.3.1
15.3.2
15.3.3
15.3.4
15.4
15.4.1
15.4.2
15.4.3
15.4.4
15.4.5
15.4.6
15.4.7
15.5
Rocks and ores 409
Introduction 409
Magmatic and metamorphic rocks and ores 409
Sediments and sedimentary rocks 412
Red beds 413
Sedimentary iron ores 416
Other sediments 420
Ferricretes and bauxites 421
Recent geological environments 422
Terrestrial surfaces 423
Spring and ground water 423
Deep sea 424
Continental shelves 424
Lakes and streams 425
Hydrothermal marine environments 427
Martian surface 429
Iron fractionation in sediments 430
Appendix 431
16
16.1
16.2
16.3
16.4
16.4.1
16.4.2
16.4.3
16.4.3.1
16.4.3.2
16.4.3.3
16.4.3.4
16.4.3.5
16.5
16.5.1
16.5.2
16.6
16.6.1
16.6.2
16.6.3
16.6.4
Soils 433
Soils – a unique environment for iron oxide formation
in terrestrial ecosystems 433
Iron oxide formation in soils 435
Iron oxide content and soil development 437
Occurrence and formation 439
Historical aspects 439
Distribution pattern 440
The various oxides 441
Goethite 441
Hematite and its association with goethite 442
Lepidocrocite, feroxyhyte and green rust 447
Ferrihydrite and its association with goethite 448
Magnetite and maghemite 450
Properties 452
Surface area, crystal morphology and size 452
Aluminium substitution 456
Significance for soil properties 459
Colour 459
Charge and redox properties 461
Anion and cation binding 463
Aggregation and cementation 468
17
17.1
17.2
Organisms 475
General 475
Biotically-mediated formation 476
XI
XII
Contents
17.2.1
17.2.2
17.2.3
17.2.3.1
17.2.3.2
17.3
Goethite and lepidocrocite 476
Ferihydrite 477
Magnetite 480
Magnetite in chitons’ teeth 481
Magnetite in bacteria and other organisms 481
Biotically induced formation 486
18
18.1
18.2
18.3
18.4
18.5
18.5.1
18.5.2
18.5.3
18.6
Products of iron metal corrosion 491
General 491
Electrochemical corrosion 491
High temperature oxidation/corrosion in gases 494
Other forms of corrosion 496
The products of corrosion 497
Iron oxides formed by electrochemical corrosion 499
Iron oxides in passive films 503
Thermally grown oxide films 504
Prevention of corrosion; protective oxide layers 506
19
19.1
19.2
19.2.1
19.2.2
19.3
19.4
19.5
19.6
19.7
Applications 509
Historical background 509
Pigments 511
Natural pigments 512
Synthetic pigments 514
Magnetic pigments 516
Ferrites 517
Catalysts 518
Other uses of iron oxides 522
Undesirable iron oxides 524
20
20.1
20.1.1
20.1.2
20.1.2.1
20.1.2.2
20.1.3
20.1.4
20.1.5
20.1.6
20.2
20.2.1
Synthesis 527
Industrial synthesis 527
General 527
Solid state transformations 528
The copperas process 528
Other solid state processes 528
Reduction of organic compounds 529
Precipitation from FeII solutions 530
Other processes 531
Magnetic pigments 532
Laboratory synthesis methods 533
Goethite 533
Other methods 533
Lepidocrocite 534
Other methods 534
Akaganéite 534
20.2.2
20.2.3
Contents
20.2.4
20.2.5
20.2.6
20.2.7
20.2.7.1
20.2.8
20.2.9
20.2.10
20.2.11
20.2.12
20.2.13
20.2.14
21
21.1
21.2
21.2.1
21.2.2
21.3
21.4
21.5
21.6
21.7
Other methods 534
Schwertmannite 535
Feroxyhyte 535
Ferrihydrite 535
2-line ferrihydrite 535
6-line ferrihydrite 535
Other methods 536
Hematite 536
Other methods 536
Coated hematite 537
e-Fe2O3 538
Magnetite 538
Other methods 538
Maghemite 539
Other methods 539
Fe(OH)2 540
Other methods 540
Green rust 540
Other compounds 541
FeO (nonstoichiometric) 541
High pressure FeOOH 541
Production of iron oxides on substrates or in confined spaces 541
Goethite, hematite and ferrihydrite 541
Magnetite 541
Precipitation of goethite, ferrihydrite or magnetite in vesicles 542
Environmental significance 543
Introduction 543
Retention of pollutants by Fe oxides in water purification
and in natural systems 544
Water treatment systems 544
Natural systems 546
Acid mine tailings 547
Detoxification reactions 549
Bacterial turnover of environmental pollutants 551
Anthropogenic dust and industrial sites 551
Iron-oxide rich waste products 552
References
555
Subject Index
651
Sources of Figures and Tables
659
XIII